Regulatory volume decrease in cultured astrocytes. I. Potassium- and chloride-activated permeability.
Regulatory volume decrease (RVD) in detached cerebellar astrocytes in culture after acute exposure to hyposmolarity was characterized in this and the accompanying paper [H. Pasantes-Morales, R. A. Murray, R. Sanches-Olea, and J. Moran. Am. J. Physiol. 266 (Cell Physiol. 35): C172-C178, 1994]. RVD was independent of extracellular calcium, was accelerated at pH 8-9 and retarded at pH 6, and was reduced at temperatures < 18 degrees C. The cationic pathway activated by hyposmolarity was specific for K+ and Rb+, since RVD was abolished and secondary swelling occurred when these ions replaced Na+. However, Li+, choline, tris(hydroxymethyl)aminomethane, and glucosamine, all as Cl- salts, did not affect RVD. The anion pathway was unselective, since RVD was inhibited when NaCl was replaced by anion K+ salts with a permeability rank of SCN- = I- > NO3- > Cl- > benzoate > acetate >> SO3- > gluconate. RVD was unaffected by bumetanide (50 microM) and weakly inhibited by furosemide (2 mM). Quinidine but not other K+ channel blockers inhibited RVD, and its effect was reversed by gramicidin. RVD was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and dipyridamole but not by diphenylamine-2-carboxylate or anthracene-9-carboxylate. These results suggest that diffusion possibly via channels rather than cotransporters is involved in the swelling-activated K+ and Cl- fluxes. Gramicidin did not change astrocyte volume in isosmotic conditions, but greatly accelerated RVD, suggesting that low Cl- permeability in isosmotic conditions markedly increases by swelling, thus making K+ permeability the rate-limiting step for RVD.
Pasantes-Morales
H
H
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City.
Murray
R A
RA
Lilja
L
L
Morán
J
J
D000818:Animals; D000838:Anions / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology* / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D002412:Cations / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D002712:Chlorides / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D011188:Potassium / Q000494:pharmacology*; D026902:Potassium Channel Blockers; D051381:Rats; D027981:Symporters; D013696:Temperature; D013997:Time Factors; D000096922:K Cl- Cotransporters
D000838:Anions; D002118:Calcium; D002352:Carrier Proteins; D002412:Cations; D018118:Chloride Channels; D002712:Chlorides; D011188:Potassium; D026902:Potassium Channel Blockers; D027981:Symporters; D000096922:K Cl- Cotransporters