THE EXCITATION-CONTRACTION COUPLING OF THE SKELETAL …

THE EXCITATION-CONTRACTION COUPLING OF THE

SKELETAL MUSCLE AND THE ' GLYCEROL EFFECT'

Toshio YAMAGUCHI, Tatsuaki MATSUSHIMA,

Masahiro FUJINO AND Torao NAGAI*

Department of Physiology, Sapporo Medical College, Sapporo

In the recent studies concerning the excitation-contraction coupling (E-C

coupling) of muscles, the close relationship between the coupling process and

both the plasma membrane and the intracellular structures joined to this mem-

brane has been assumed (HUXLEY, 195913); MASHIMA, 195919)).

Further, it is well known that glycerol is a constitutional member of lipid

part in lipoprotein molecule, which is a constituent substance not only of the

plasma membrane but also of the intracellular membrane systems (DANIELLI,19585)). On the other hand, in the study of muscle contraction, glycerol treated

muscles have been used widely (SENT-GYORGYI, 195124)) and are prepared by

treating fresh muscles with glycerol solution of high concentration for a long

time, so that the muscle membranes are considered to be completely destroyed,

though the contractile elements are not suffered greatly (KOREY, 195015)).

Considering these points, it could be expected that a short treatment of muscle

with glycerol of a suitable concentration caused a moderate alteration of the

plasma membrane of muscle cells and the joining structures to the membraneso that the alteration would give rise to some change in the E-C coupling

process in question. It is from this view point that the present study was

undertaken to clarify the mechanism of the coupling process. In the present

study performed on the effects of glycerol of moderate concentrations contained

in Ringer solution on the electrical and mechanical responses of frog's muscles,

an interesting phenomenon, which could clarify the mechanism of the E-C

coupling process, was found, and the following description will be made mainly

on this phenomenon, which will be called 'glycerol effect'.

MATERIALS AND METHODS

Materials and preparations Experiments were performed on muscles of hind legs,

ventral abdomen, and heart ventricle of frog (Rana nigromaculata or R. japonica).For the experimental purposes, muscle fibre bundles, single muscle fibres or whole

Received for publication October 1, 1961* 山口俊夫,松島達明,藤野和宏,永井寅男

129

130 T. YAMAGUCHI, T. MATSUSHITA, M. FUJINO AND T. NAGAI

muscles were prepared; the bundles and single fibres were obtained from M. semiten-

dinosus, M. iliofibularis, or from M. rectus formis anticus, and as a whole muscle the

sartorius was used. Preparation of rectus abdominis muscle was a strip of 5mm in

width dissected from shoulder girdle to pelvic along median line. Heart ventricle

strip was prepared in the same way as described by KOTOWSKI, et al. (1959).16)Recording of transmembrane potentials The muscle bundle preparation was suspended

at both tendons on movable hooked glass rods in a trough. Intracellular glass capillary

electrodes filled with 3M KCl (electrial resistance, 10-30Mƒ¶) were inserted into single

muscle fibres of the bundle under a microscope by means of a micromanipulator. The

potential differences were fed into the balanced d. c. amplifier set in a dual oscilloscopethrough a cathode follower preamplifier.

The transmembrane potentials traced on the Broun tube was photographed. An

Ag-AgCl plate immersed in the Ringer pool, serving as the indifferent electrode, was

grounded by way of a calibration circuit.

Recording of mechanical responses The twitch tensions of a single muscle fibre were

recorded by means of a mechano-electronic transducer (RCA 5734). The single musclefibre was mounted in the above trough in the following procedures; first a tendon of

the fibre was hooked to one of the above glass rods and the other tendon was on a

hooked glass capillary lever of 4cm in length, which was attached to the movable

anode of the transducer. The fibre was, then, stretched just tautly and horizontallyin the pool. The voltage change induced by the tension development of the fibre

was fed into the oscilloscope and photographed. The resonance frequency of the trans-

ducer with its glass lever was 250 cycle, and its damping was small. This did not

cause any appreciable distortion of the recording of the twitch responses.

In order to record the tensions developed in the rectus abdominis and heart yen-

tricle strips, the preparations were mounted vertically in the cylindrical trough and

their lower ends were fixed on a hook at the lower part of the trough and their upper

ends were connected with silk thread to the glass capillary lever of 1 cm in length,

which was attached to the movable anode of the transducer. The output voltage was

fed into a balanced d. c. amplifier and recorded by an ink writing oscillograph.

The contraction height of sartorius muscle was recorded on a smoked drum of a

kymograph by means of an isotonic lever.

Stimulation system The muscles were stimulated with square pulses generated

from an electronic stimulator through Ag-AgCl wire electrodes, unless stated otherwise.

When the transmembrane potentials were recorded, the pulses were isolated from

ground by an isolating circuit, in order to minimize the stimulus artifact.Exchanging the solutions The trough employed for recording potentials and tensions

of single muscle fibres had a capacity of 6.5ml. For exchanging solutions in this

trough, sucking and pouring were carried out simultaneously by the use of two syringes

of 20ml which were operated as one unit (FURUKAWA, 1957).9) On exchanging thesolutions, they flowed along the fibre through the narrow spaces made by septa in the

trough, so that a mechanical distortion by the flow on the fibres was negligible. By

introducing dye, the residue after exchanging the solution was estimated at 1/25 of thetotal content in the trough, which was negligible for the purpose of the experiments.

In the experiments of the whole muscle and both strips of rectus abdominis and

heart ventricle, cylindrical trough was used. In this case, after the solution in the

trough was drawn out by opening the outlet at the bottom, another solution was poured

into from the upper.

Measurement of muscle weight Before the measurement was done every three mi-

nutes by means of a torsion balance, the sartorius muscles, which were just taken out

from the bathing solution, were blotted at both sides, turning several times on a

E-C COUPLING AND 'GLYCEROL EFFECT' 131

piece of filter paper. After the muscle reached to equilibrium state or showing con-stant weight, the bathing solution was exchanged for 420mM glycerol Ringer solution

(see below) or for the other hypertonic Ringer solution made by adding excess sodiumchloride.

Solutions The normal Ringer solution had the following composition NaCl, 122mM;

KH2PO4, 2mM; CaCl2, 1.3mM; and NaHCO3, 1.4mM; and it was buffered by adding

M/8 NaHCO3. 420mM glycerol Ringer solution was made by adding suitable amounts ofboth 3M glycerol solution and deionized water to 10 times hypertonic Ringer solution;

that is, a part of water of normal Ringer solution was replaced by glycerol and the

final concentration of glycerol was 420mM. The other Ringer solutions, which contained

substances to be tested, were also made in the similar way.

All experiments were performed at room temperature (17-25•Ž).

RESULTS

I. Resting and action potentials of single muscle fibres immersed in 420mM

glycerol Ringer solution This experiment was performed on eight muscle fibrebundle preparations. At first, resting and action potentials were recorded from 1-3

fibres of each bundle in normal Ringer solution. Magnitudes of resting poten-

tials, which were determined before the stimuli were given, amounted to 82-

97mV and the average value for them 90mV (1•}0.1). The action potentials

had the spike height of 123-148mV and the average value was 133mV (1•}0.16).

Then, after exchanging for the glycerol Ringer solution, recording of the poten-

tials was carried out with consideration of time elapsed. FIG. 1 represents the

FIG. 1. Magnitudes of resting and action potentials (up to

peak) obtained from single muscle fibres of frog in 420mMglycerol Ringer solution. Solid circles, resting potentials: hol-

low circles, action potentials. RP and AP indicate average

values of resting and action potentials in normal solution, res-

pectively. Abscissa, time after exchanging the solution in

min: ordinate, potential values in mV. For further explanation,

see text.

132 T. YAMAGUCHI, T. MATSUSHITA, M. FUJIN() AND T. NAGAI

Record A Record B

FIG. 2. Electrical and mechanical responses of single muscle fibres of frog

at different times after exchanging the bathing solution for420 mM glycerol

Ringer solution.

Record A. action potentials recorded with intracellular capillary electrode.

1, control response in normal Ringer, dislodging the electrode caused by move-

ment of fibres results in displacement of tracing to 0mV at right hand-side

2-5, responses in 420mM glycerol solution at 3, 24, 45 and 60min after exchang-

ing the solution, respectively.

Record B, mechanical response from one single muscle fibre. 1, control

response in normal Ringer 2-5, responses in 420mM glycerol at 1, 24, 44 and

60min after exchanging the solution, respectively.


values thus obtained. The result shows that the magnitudes of resting poten-

tials recorded for about sixty minutes coincide with those of the control. The

same conclusion is deduced from the result of the spike heights of action poten-

tials although they are dispersed somewhat widely.

Sixteen muscle fibres tested showed a great difference in their maximum

rates of rise of action potentials recorded in normal Ringer solution and the

rates amounted to 238-800V/sec, ten of them 200-450V/sec. During the time

of about sixty minutes, most fibres immersed in the glycerol Ringer solution

showed the value of 200-450V/sec. It can be said, therefore, that glycerol Ringer

solution has no effect on the maximum rate of rise.

The maximum rates of fall of action potentials in normal Ringer solution,

amounting to 48-182V/sec, were obtained from 17 fibres and the values from

13 fibres of them ranged from 48 to 113 V/sec. During about sixty minutes,

the values in the glycerol Ringer solution were in the latter range. But, as a

whole, for initial twenty minutes, the values were decreased by a little. This

may suggest that glycerol Ringer solution seems to have a possibility of in-

fluencing on the maximum rate of fall.

FIG. 2-A shows a typical example of electrical phenomenon of single muscle

fibres immersed in normal Ringer solution and at various times immersed in

420 mM glycerol Ringer solution.

II. Mechanical responses and weight of muscles in some hypertonic Ringer solutions

a) Twitch tensions of single muscle fibre immersed in 420mM glycerol Ringer

solution After recording the twitch tension in normal Ringer solution, a short-

ly lasting fibrillation occurred when the normal Ringer solution was exchanged

for the 420mM glycerol one. For the first some minutes under the latter con-

dition the mechanical twitch responses to electrical stimuli diminished greatly

and the twitch tension showed only 0-5 percent of that in normal Ringer

solution; but at this time, excitability remained unaltered, as shown in FIG.

2-A. These facts indicate, therefore, that in the glycerol Ringer solution,

muscle fibre does not contract, although the cell membrane maintains normal

excitability (FIG. 1, 2-A).It has been already reported that such phenomenon due to the hypertonic

conditions occurs (HODGKIN and HOROWICZ, 195711); HOWARTH, 195812)). But

the peculiar evidence found in the present experiment is that the contraction,

which has been once diminished or abolished, is restored again; twitch tension

begins to increase in several minutes after exchanging the solution, and after

50-60 minutes reaches the maximum, which amounts to 60-70 percent of that

in normal Ringer solution. The rising time of the twitch in the glycerol Rin-

ger solution was 1.5-2.5 times longer than that in the normal Ringer solution.

FIG. 2-B shows a typical example of the results mentioned here.

b) The mechanical responses and weight of whole muscles immersed in glyce-rol Ringer solutions The experiment on isotonic contraction of the whole mus-


cle in the glycerol Ringer solution yielded the almost same result as the above.

On exchanging the Ringer solutions for the glycerol one, small contracture

occurred. For the first several minutes, the twitch heights responding to the

successive single stimuli diminished gradually with the time lapse and then

they were restored again (FIG. 3).

FIG. 3. Diminution and restora-

tion of successive twitch heights of

sartorius muscle in 420mM glycerol

Ringer solution. The muscle was

stimulated every 5 min. Arrow mark

indicates the time exchanging the

bathing solution for glycerol Ringer

solution.

The diminution of twitch responses, which appeared just after the ex-

changing the bathing solution, was abrupt in the case of a single muscle fibre,

but gradual in the case of whole muscle. This may be due to the time re-

quiring for glycerol to diffuse into the extracellular spaces in whole muscle:

the effects of glycerol on the fibres situated at the surface may occur earlier

than that on the inner ones of the muscle, so that in the case of whole mus-

cle the contraction recorded may express the total of responses of all the fibres

(FRANK, 1960)8).The above phenomenon of restoration in the twitch responses was able to

be observed in a considerable wide range of concentrations of glycerol contain-

ed in the Ringer solutions, and the most prominent phenomenon was induced

in 420mM glycerol Ringer solution; the restoration in 840mM became indistinct

due to the decrease of its grade, while that in 120mM due to the less dimi-

nution of the initial twitch responses.

The beginning and the duration of the increase of the twitch responses

did not depend on the stimulus intervals 1-9 min, but only on the duration of

immersion of the muscle in glycerol Ringer solutions.

The restoration of contractility of the muscle immersed in glycerol Ringer

solution was able to be observed also in the case of a short complete tetanus.

In 420mM glycerol Ringer solution, the weight of sartorius muscle dropped

rapidly and, in a few minutes, it reached the minimum value, which was 74-

82 percent of that in normal Ringer solution. After reaching the minimum,

the weight was kept constant for about an hour and returned to the initial,

when the muscle was replaced in normal Ringer solution (FIG. 4). Namely, the

restoration of contractility already appeared, while the osmotic effect was


FIG. 4. Decrease in weight of

sartorius muscle in 420mM glycerol

Ringer solution, and restoration

after returning to normal solution.

FIG. 5. Mechanical responses of rectus abdominis strip (A)and heart ventricle strip (B) to electrical stimulation in glycerolRinger solutions.

kept constant from several minutes to scores after immersion in the hypertonic

glycerol Ringer solution.

c) The mechanical responses of rectus abdominis muscle and heart ventricle

muscle immersed in the glycerol Ringer solution The result of the mechanical

responses in 420mM glycerol Ringer solution to electrical stimuli of the rectus


abdominis strip, of which muscle is reported to belong to slow fibre system

(KUFFLER & VAUGHAN WILLIAMS, 1953'7)), was just the same as that of sartoriusmuscle or others from hind leg, which are constituted from fast fibres pre-

dominantly.17) FIG. 5-A shows the result obtained from rectus abdominis strip.

Differing from the skeletal muscle, the heart ventricle strip did not show

the restored mechanical responses to electrical stimuli in hypertonic glycerol

Ringer solutions and the tensions developed were diminished only with the

time elapsed. The higher the concentration of glycerol in the solution, the

more rapidly the twitch responses were diminished, and were abolished in five

minutes in 2M glycerol Ringer solution (FIG. 5-B).

d) The mechanical responses of whole muscle in hypertonic Ringer solutions

made by other substances It was found that the twitch heights of sartorius

muscles diminished only with time elapsed in hypertonic Ringer solutions made

by the following concentrations of the substances, 150-255 mM NaCl, 50-400 mM

mannitol, 200-400mM glucose, 50-300mM monoacetin (CH2OH•ECHOHCH2OCOCH3)

and 200-300mM sucrose, respectively (FIG. 6). Such phenomenon obtained in

muscles in hypertonic Ringer solutions has been already investigated by several

FIG. 6. Diminutions of twitch heights of sartorius muscles in some hyper-

tonic Ringer solutions. A, 150mM NaCl: B, 100mM mannitol: C, 200mM

glucose: D, 50mM monoacetin: E, 200mM sucrose. Arrow marks indicate the

time exchanging the solutions; the muscles were stimulated every one min if

B and D, and every two in A, C and E. Rotation speeds of smoked drums were

changed at "a".

F-C COUPLING AND 'GLYCEROL EFFECT' 137

authors as afore mentioned (see p.134).

The twitch height of sartorius, which had previously been diminished by

immersing in 255mM NaCl-Ringer solution, was restored after exchanging the

bathing solution for the Ringer solution made more hypertonic by the addition

of 420mM glycerol. Under the former condition, the weight of muscle kept 80

percent of that in normal, while under the latter, it decreased further by 5

percent.

Unlike these substances, only urea showed a similar effect to the case of

glycerol Ringer solution, but the effect was not so remarkable. As soon as

the bathing solution was exchanged for 400mM urea solution, which had about

the same tonicity as the glycerol Ringer solution, the sartorius showed a con-

tracture and then relaxed very slowly. The twitch responses superimposed on

this shortening were abolished after about four minutes. In about fifteen

minutes, however, there appeared just a discriminative mechanical responses,

which increased by and by and thirty minutes after exchanging the solution,

reached the maximum which was sustained.

But the height was much smaller than those in the glycerol Ringer solution

(FIG. 7). With higher concentrations of urea, the greater became the contractureand also the later the time of reappearance of mechanical responses became;

at last restoration could not be seen in the Ringer solutions containing more

than 800mM urea.

FIG. 7. Abolition and restora-

tion of successive twitch responses

of sartorius muscle in 400mM urea

Ringer solution. The muscle was

stimulated by 0.1cps square pulses

through Ag-AgCl wire electrodes.

e) Effect of glycerol on the mechanical responses of whole muscle to A. C.

electric field stimulation under excess K+ condition The effect of glycerol on themechanical responses to the A. C. electric field stimulation under the condition

of partially depolarized sartorius muscle by excess K+ (CSAPO & SUZUKI, 1958;

STEN-KNUDSEN, 196022)), was investigated. The excess K+-Ringer solution was

made by replacing a part of NaCl with KCl, and the final concentration of

potassium was 13mM. The hypertonic glycerol solution used in this experiment

was made so as to contain glycerol of 420mM in the excess K+ Ringer solution.

The muscle was stimulated at appropriate intervals by A. C. electric field

(50cps; 8-10V/cm; duration of 94msec) along both transverse and longitudinal


directions of the fibres. The duration of the stimulation was determined by

means of a Helmholz pendulum, and platinum plates were employed as massive

electrodes. Even under the condition of the excess K+ solution, the increase

of the mechanical responses mentioned above followed their diminution in the

glycerol solution. The result obtained by the longitudinal stimulation is shown

in FIG. 8.

FIG. 8. Abolition and restoration

of successive twitch responses of sar-

torius muscle recorded isotonically in

Ringer solution containing 13mM K.

The muscle was stimulated every 5

min by longitudinal A. C. electric field.

For further explanation, see text.

DISCUSSION

It was already known that, under hypertonic conditions, the action potentials

of skeletal muscle fibres were elicited (Ismico and SATO, 19571) and the me-chanical responses of muscles were diminished or abolished finally (FENN, 1936'3);

HOWARTH, 195812)).

Furthermore, by the simultaneous recordings of electrical and mechanical

responses from a single muscle fibre, HODGKIN and HOROWICZ (1957)11) have

emphasized that these two events were differentiated each other due to the

hypertonic condition. The same result was also reported by LASZLO (1958)18) on

gastrocnemius muscle. Especially, the former authors have mentioned that

under the hypertonic condition the mechanical twitch responses of the single

muscle fibres are diminished with time elapsed and are abolished in 15-90

minutes while the action potential persists.

The phenomenon in the present paper is, however, different from the results

reported already and very peculiar in the point that, in the Ringer solution

made hypertonic by glycerol, the mechanical response of the twitch, which has

been once diminished or abolished, is restored with time elapsed even under

dehydrated state (FIG. 4). The evidence would not support the view presented

by HOWARTH (1958)12) that the tonicity of the outer medium does not block the

link between the excitation of membrane and contraction process, and that

although the contractile system is activated, the decline of isometric tension

may also be a result of the changed ionic concentrations within the fibre. From

E-C COUPLING AND GLYCEROL EFFECT 139

the results of the present study, however, it would be indicated that the hyper-

tonicity of the outer medium suppresses or blocks the link between excitation

and contraction, and on the other hand the link is restored by actions of gly-

cerol. MASHIMA (1959)19) has also stated that the hypertonicity may block theE-C coupling based on the fact that caffeine produces contracture on the muscle

even in hypertonic Ringer solutions.

The above restoration of the twitch response of the skeletal muscles ob-

served in the glycerol Ringer solution could not be seen in other hypertonic

Ringer solutions made by substances except urea. This suggests that the

above phenomenon is considerably specific for glycerol and it may be suitable

to call the phenomenon 'glycerol effect'.

BOZLER pointed out (personal communication, 1960) that it could not be

considered that substances, which had the molecular weight as that of glycerol,

could not penetrate into the muscle cells within the time when the mechanical

responses were restored. This may be supposed by the result shown in FIG. 4

on muscle weight: any increase of the muscle weight does not occur in glycerol

Ringer solution over the wide range of the time course. Therefore, two possible

causes of the 'glycerol effect' are considered: the one is the effect of the

glycerol on the membrane itself, and another is that, though glycerol penetrates

into the cell, the glycerol is localized in a portion within the cell, which is in

the vicinity of the membrane and the amount of the penetrated glycerol is so

small that it causes no change in weight. In other words, the 'glycerol effect'

would occur in connection with the membrane or a portion in its vicinity.

It can be considered generally that the mechanism in the 'glycerol effect'

is either chemical or physicochemical. In order to clarify which of the two is

concerned, further experiment was performed by the use of urea, of which

molecular weight is smaller than glycerol. The result, that showed a similar

phenomenon as 'glycerol effect' might suggest that the mechanism of the'glycerol effect' is more physicochemical rather than chemical

.

But, even if so, one problem still remains unsolved. According to the pre-

sent result on urea, the time of beginning of the restoration of the twitch

response was retarded much more and the heights of them were much smaller

than the case of glycerol. Considering that a relatively large amount of urea

penetrates into cells in a short time (BOZLER, 19593) BARANY, et al., 19602)),urea must come to the membrane or a portion of the cell in the vicinity of the

membrane much faster, and thus restoration of the twitch response must occur

in the earlier stage. A possible explanation for this inconsistency is that the

effect of urea may be weaker than that of glycerol. But, we cannot exclude

the possibility that the urea might have directly an inhibitory influence on

actomyosin system (BARANY, et al., 19602)).

KUFFLER and VAUGHAN WILLIAMS (1953)' discussed the differences of the

physiological properties between fast and slow fibres of the skeletal muscle, and


according to PAUSCHINGER (1960),21) one of the differences may be due to the

difference of the content of calcium ion. From the result that no difference

could be seen between the two kinds of muscle fibres in connection with'glycerol effect' it is suggested that the 'glycerol effect' may be independent

of the Ca content of muscles.

It is considered that the contractions of both skeletal and heart muscles

are initiated by depolarization of membrane potentials (FRANK, 19607); NIEDER-

GERKE, 195920)). On the other hand, SUZUKI23) has suggested that there is some

differences between the two muscles with respect to the mechanism in the E-C

coupling; namely, from the experiments performed by employing caffeine, which

induces contracture without depolarization, it was shown that in the case of

skeletal muscles contracture could be elicited under the Ca free condition

(FRANK, 19607); AXELSSON and THESLEFF, 19581)), while Suzum23) demonstratedthe necessity of Ca++ to induce the contracture of the heart ventricle muscles.

The present result that the 'glycerol effect' did not occur on heart ventricle

muscle is the additional interesting evidence to the above facts that there

would be different mechanism between the E-C couplings of the two muscles.

The 'glycerol effect' was produced in the case of the A. C. stimulation on

sartorius muscle under excess K+ condition. Based on the results obtained by

A. C field stimulation of muscle under the same K+ condition it has been dis-

cussed in detail by CSAPO and SUZUKI (1958)4), STEN-KNUDSEN (1960)22) or by

others, how muscle contraction is operated. The present result would suggest

that the affected part by electric currents, whether they are longitudinal or

transverse, is the membrane or its vicinity and not the contractile system

within the cell.

SUMMARY

In order to clarify the mechanism of E-C coupling process of the muscle,

electrical and mechanical responses to the electrical stimulation and the relation-

ship between their changes and the muscle weight were investigated in Ringer

solution made hypertonic by the addition of glycerol or of the other several

substances.

1. For about sixty minutes, for which the observation was made, features of

resting and action potentials from single muscle fibres in 420mM glycerol

Ringer solution were almost the same as those in normal Ringer solution.

2. The mechanical twitch responses of sartorius muscle immersed in glycerol

Ringer solution were at first diminished and then restored with time elapsed.

The most prominent restoration occurred in 420mM glycerol Ringer solution,

and the maximum restored twitch tension of a single fibre, which attained to

50-60 minutes after exchanging the bathing solution for glycerol one, was 60-70

percent of that in normal Ringer solution.


3. In 420mM glycerol Ringer solution, the weight of sartorius muscle dropped

to 74-82 percent of that in normal Ringer solution within a few minutes, and

then the dropped value kept constant for about an hour.

4. The similar mechanical phenomenon was observed in rectus abdominis muscle

but not in heart ventricle. It was also found in partially depolarized sartorius

muscle stimulated by A. C. electric field.

5. The restoration of the mechanical twitch response did not occur in sartorius

muscles under the condition of Ringer solutions made hypertonic by the addi-

tion of excess NaCl, mannitol, glucose, monoacetin and sucrose respectively,

and the observable change was only a gradual diminution of mechanical twitch

response. In the case of urea Ringer solution, however, the restoration ap-

peared, though the grade was considerably less than that in glycerol.

6. From these results, the mechanism of the peculiar effect of glycerol was

discussed in connection with the excitation-contraction coupling process of

muscle.

REFERENCES

1) AXELSSON, J. AND THESLEFF, S. Activation of the contractile mechanism in striatedmuscle. Acta Physiol. Scand. 44: 55-66, 1958.

2) BARANY, M., BARANY, K. UND TRAUTWEIN, W. Hemmung der Aktin-L-MyosinInteraktion in lebenden und extrahierten Muskeln durch Urea. Biochim. Biophys.

Acta 45: 317-335, 1960.

3) BOZLER, E. Osmotic effects and diffusion of nonelectrolytes in muscle. Am. J. Phy-siol. 197: 505-510, 1959.

4) CSAPO, A. AND SUZUKI, T. The effectiveness of the longitudinal field, coupledwith depolarization in activating frog twitch muscles. J. gen. Physiol. 41: 1083-1098,

1958.

5) DANIELLI, J. F. Surface Phenomena in Chemistry and Biology DANIELLI, J. F., PANK-HURST, K. G. A. AND RIDDIFORD, A. C. (editors), p.246. Pergamon Press, London,1958.

6) FENN, W. O. The role of tissue spaces in the osmotic equilibrium of frog musclesin hypotonic and hypertonic solutions. J. cell. comp. Physiol. 9: 93-103, 1936.

7) FRANK, G. B. Effects of changes in extracellular calcium concentration on the

potassium induced contracture of frogs skeletal muscle. J. Physiol. 151: 518-538,1960.

8) FRANK, G. B. Maximum activation of the contractile mechanism in frog's skeletalmuscle by potassium depolarization. J. Physiol. 154: 345-353, 1960.

9) FURUKAWA, T. [Guide to the Microelectrode Technique[ (Japanese). p.107, KinpodoPublishing Co., Ltd., Tokyo. 1957.

10) HAUROWITZ, F. Chemistry and Biology of Proteins. Academic Press, New York. 1950.11) HODGKIN, A. L. AND HOROWICZ, P.The differential action of hypertonic solutions

on the twitch and action potential of a muscle fibre. J. Physiol. 136: 17 p.1957.

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14) ISHIKO, N. AND SATO, M. The effect of calcium ions on electrical properties ofstriated muscle fibres. Jap. J. Physiol. 7: 51-63, 1957.

15) KOREY, S. Some factors influencing the contractility of a nonconducting fiber prepar-ation. Biochim. Biophys. Acta 4: 58-67, 1950.

16) KOTOWSKI, H., ANTONI, H. UND FLECKENSTEIN, A. Elektrophysiologische Studienzur Aufhebung der Kaliumlahmung des Froschmyocards durch ATP. Pfliigers Arch.

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17) KUFFLER, S. W. AND VAUGHAN WILLIAMS, E. M. Properties of the " slow " skeletalmuscle fibres of the frog. J. Physiol. 121: 318-340, 1953.

18) LASZLO, N. Die Muskeltatigkeit p. 295. Ernst, E. (author) Verlag d. UngarischenAkademie d. Wissenschaf ten, Budapest. 1958.

19) MASHIMA, H. On the excitation-contraction coupling in the skeletal muscle. (Japa-nese). Medicine of Japan in 1959 5: 333-340, 1959.

20) NIEDERGERKE, R. Calcium and the activation of contraction. Experientia 15: 128-130, 1959.

21) PAUSCHINGER, P. Uber die Beeinflussung von Kontrakturen langsamer (tonischer)and schneller (phasischer) Skeletmuskeln durch Calcium. Pfliigers Arch. ges. Physiol.272: 43-44, 1960.

22) STEN-KNUDSEN, O. Is muscle contraction initiated by internal current flow? J.Physiol. 151: 363-384, 1960.

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