Hafez M. BazaraaMMXXI

Chloride channelopathies

l Na depolarisationl K repolarisationElectrochemical concordance è effluxThen Na/K pump è influx

Na: least permeability

l Calcium (slow) depolarisationl Chloride (muscle) repolarisationConc è INElectric è OUT (=in at -70mV)↑ permeability è stabilization effect

Na: least permeability

l CHANNELSPassive ion pores

l CO-TRANSPORTERS

SymportersAntiporters (exchangers)

l PUMPSActive

transporters(ATP)

Basolateral active Na/K exchange(most renal energy)

Apical Na transportl Follows conc. gradientl Secondary transporters-Na coupled cotransport-ENaC-Na/H exchanger

Loudon & Fry. Ann Clin Biochem. 2014

Loudon & Fry. Ann Clin Biochem. 2014

Bartter syndrome

Renal salt wasting

↑ renin, aldosterone

HypoK metabolic alkalosis

Expressed in inner ear

Gitelman syndrome

l SLC2A3 mutation è NCCT thiazide sensitive NaCl cotransporter

l ClCNKB mutation è ClC-KB

Na Cl Mg K (ALD) wasting↓Mg è ↓Ca (PTH)

PCT receptor-mediated endocytosis

Electrogenic vacuolar

H ATPase

ClC-5HHHH

HHHH+Cl- ClClCl

Apical

Endosome

ClC-5

l Kidneys (mainly PCT) & Intestinel Cl/H exchanger, apical endosomesl Maintains acidification/ activationl Cl dissipates high +ve intraluminal potential

ClC-5: Dent’s disease (XLR)

l Filtered LMW proteins è PCT endocytosisXXXX LMW tubular proteinuriaα1-microglobulinuria to microalbuminuria close to or above 1

l PTH & bound vit D è endocytosisXXXX ↑ PTH & ↑ Vit D activationHyperphosphaturia, hypercalcuria, stones & NCRenal glucosuria, aminoaciduria

l CLCN5 gene mutation è Dent’s disease type Il OCRL1 gene mutation è Dent’s disease type IIl . è Lowe syndrome

Inositol Polyphosphate-5-Phosphatase

Involved in regulating membrane traffickingNumerous subcellular locations including endosomes & plasma membrane. May also play a role in primary cilium formation.

l Electrical activity– Voltage-gated– Ligand-gated GABA, Gly

l Salt transport– Renal– CFTR, , SLC26A3

l Intracellular Cl/H exch. (organoids)– Dent– Storage

EXTRA-RENAL

l Electrical activity– Voltage-gated– Ligand-gated GABA, Gly

l Salt transport– Renal– CFTR , SLC26A3

l Intracellular Cl/H exch. (organoids)– Dent– Storage

Voltage-gated ClC-0 cloned (1990)

l Torpedo marmorata

è ClCN genes coding ClC proteins-Plasma membrane channels-Cl/H exchangers NOT strictly channelopathies

Myotonia

Myotonia congenita

AD ThomsenAR Becker

l ClC1 in skeletal musclel Voltage-gated Cl channell Repolarisation & stabilization

l Chloride (muscle) repolarisationConc è INElectric è OUT (=in at -70mV)↑ permeability è stabilization effect

Ligand-gated Cl channelopathies

ClC-2l CNS: GABA-A receptors è ↑ intracellular Cl è Inhibitory

Proposed relation to epilepsy (3q26)l Widely expressed

Unproven relation to lung development, gastric secretionl Mice: leukoencephalopathy, blindness, testicular

degeneration

Ligand-gated Cl channelopathies

Hereditary hyperekplexia (stiff baby syndrome)l ↑ startle response to mild stimuli (visual, aud.,

tactile)l Hypertonia (during no voluntary movement possible)l Laryngospasm, apnea may occur. ?SIDSl Glycine-mediated (GLRA1 mutation)

EXTRA-RENAL

l Electrical activity– Voltage-gated– Ligand-gated GABA, Gly

l Salt transport– Renal– CFTR , SLC26A3

l Intracellular Cl/H exch. (organoids)– Dent– Storage

ClC-7

l Widely expressed, lysosomesl Osteopetrosis (polymorphisms BMD)l Lysosomal storage & neurodegenerationl Retinal degeneration

EXTRA-RENALl Electrical activity

– Voltage-gated– Ligand-gated GABA, Gly

l Salt transport– Renal– CFTR, SLC26A3

l Intracellular Cl/H exch. (organoids)– Dent– Storage

CFTR

C F Transmembrane (conductance) Regulator

Phosphorylation-dependent (cAMP) apical Cl channell The most common hereditary lethal disease in Caucasians

(1:3000)l Abnormal epithelial salt/ water transportl ENaC dys(up)regulationl Resp., enterocytes, gland acini, pancreas, vas deferens, …

CFTR (lung ionocytes)

Abnormal CFTR allows Cl influx but not efflux↓ Cl, Na, H2O in secretions

Congenital Chloride (losing) Diarrhea

l Solute linked carrier

SLC26A3 Membrane anion exchanger

Congenital Chloride (losing) Diarrhea

l Solute linked carrier SLC26A3Membrane anion (Cl/HCO3 exchanger)

l Watery diarrhea with low pH & high Cl contentl Hypochloremic metabolic alkalosisBUTYRATE:↑ intestinal water and ion absorption through a variety of

mechanisms, including the activation of a parallel Cl-/butyrate and Na+/H+ exchanger.

New targeted therapies may be under way….

l Mexiletene & Lamotrigine: Voltage-gated Na channel blockers. Proposed for myotonia.

l Targets F508 deletion in CF:The newly approved medication combines two “corrector” molecules (elexacaftor and tezacaftor) that address protein misfolding plus a “potentiator” (ivacaftor) that improves chloride channel opening.

CONCLUSION

l Don’t overlook anionsl Chloride transport:

– Salt & water reabsorption– Epithelial salt & water transport– Electrical activity– Endosome & Lysosome function

l There’s a lot we don’t know

Q1

A zeroB inwards according to concentration gradientC outwards according to electrical gradient D outwards by active transport

Under basal (resting) conditions, the net movement of chloride ions across the cell membrane is

Q2

A Bartter syndromeB Nephrogenic diabetes incipidus C Myotonia congenitaD Cystic fibrosis

Disorders of chloride channels/ chloride transport are implicated in the following conditions EXCEPT

Q3

A the presence of abnormal proteins in plasmaB increased glomerular permeability C impaired tubular reabsorptionD losses from the urinary tract

The main mechanism of proteinuria in Dent disease is