Isovolumetric regulation mechanisms in cultured cerebellar granule neurons

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Abstract

Cultured cerebellar granule neurons exposed to gradual reductions in osmolarity (-1.8 mOsm/min) maintained constant volume up to -50% external osmolarity (πo), 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 πo -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 πo. Cl--free medium impaired IVR when πo decreased to -24% and Ba2+ blocked it only at a late phase of -30% πo. 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 πo 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% πo); and (iv), K+ fluxes do not contribute to IVR until a late phase (

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Tuz, K., Ordaz, B., Vaca, L., Quesada, O., & Pasantes-Morales, H. (2001). Isovolumetric regulation mechanisms in cultured cerebellar granule neurons. Journal of Neurochemistry, 79(1), 143–151. https://doi.org/10.1046/j.1471-4159.2001.00546.x

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