Isovolumetric regulation mechanisms in cultured cerebellar granule neurons.
Cultured cerebellar granule neurons exposed to gradual reductions in osmolarity (-1.8 mOsm/min) maintained constant volume up to -50% external osmolarity (pi(o)), showing the occurrence of isovolumetric regulation (IVR). Amino acids, Cl-, and K+ contributed at different phases of IVR, with early efflux threshold for [3H]taurine, D-[3H]aspartate (as marker for glutamate) of pi(o) -2% and -19%, respectively, and more delayed thresholds of -30% for [3H]glycine and -25% and -29%, respectively, for Cl- (125I) and K+ (86Rb). Taurine seems preferentially involved in IVR, showing the lowest threshold, the highest efflux rate (five-fold over other amino acids) and the largest cell content decrease. Taurine and Cl- efflux were abolished by niflumic acid and 86Rb by 15 mM Ba2+. Niflumic acid essentially prevented IVR in all ranges of pi(o). Cl--free medium impaired IVR when pi(o) decreased to -24% and Ba2+ blocked it only at a late phase of -30% pi(o). These results indicate that in cerebellar granule neurons: (i) IVR is an active process of volume regulation accomplished by efflux of intracellular osmolytes; (ii) the volume regulation operating at small changes of pi(o) is fully accounted for by mechanisms sensitive to niflumic acid, with contributions of both Cl- and amino acids, particularly taurine; (iii) Cl- contribution to IVR is delayed with respect to other niflumic acid-sensitive osmolyte fluxes (osmolarity threshold of -25% pi(o)); and (iv), K+ fluxes do not contribute to IVR until a late phase (< -30% pi(o)).
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Department of Biophysics, Institute of Cell Physiology, National University of Mexico, Mexico City, Mexico.
Ordaz
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Vaca
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Quesada
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Pasantes-Morales
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D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001464:Barium / Q000494:pharmacology; D048429:Cell Size; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology*; D002712:Chlorides / Q000008:administration & dosage / Q000378:metabolism; D003470:Culture Media; D007457:Iodine Radioisotopes / Q000378:metabolism; D009474:Neurons / Q000502:physiology*; D009544:Niflumic Acid / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012414:Rubidium Radioisotopes / Q000378:metabolism; D013654:Taurine / Q000378:metabolism; D014882:Water-Electrolyte Balance
D000596:Amino Acids; D002712:Chlorides; D003470:Culture Media; D007457:Iodine Radioisotopes; D012414:Rubidium Radioisotopes; D013654:Taurine; D001464:Barium; D009544:Niflumic Acid; D011188:Potassium