Isovolumetric regulation mechanisms in cultured cerebellar granule neurons

  • Tuz K
  • Ordaz B
  • Vaca L
 et al. 
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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 (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)).

Author-supplied keywords

  • Amino Acids/metabolism
  • Animals
  • Barium/pharmacology
  • Cell Size
  • Cells
  • Cerebellum/ cytology
  • Chlorides/administration {&} dosage/metabolism
  • Culture Media
  • Cultured
  • Iodine Radioisotopes/metabolism
  • Neurons/ physiology
  • Niflumic Acid/pharmacology
  • Osmolar Concentration
  • Potassium/metabolism
  • Rats
  • Rubidium Radioisotopes/metabolism
  • Taurine/metabolism
  • Water-Electrolyte Balance

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Authors

  • K Tuz

  • B Ordaz

  • L Vaca

  • O Quesada

  • H Pasantes-Morales

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