Neurons respond to hyposmotic conditions by an increase in intracellular free calcium.
The effect of hyposmotic conditions on the concentration of intracellular free calcium ([Ca2+]i) was studied in cultured cerebellar granule cells and cerebral cortical neurons after loading of the cells with the fluorescent Ca2+ chelator Fluo-3. It was found that in both types of neurons exposure to media with a decrease in osmolarity of 20 to 50% of the osmolarity in the isosmotic medium (320 mOsm) led to a dose dependent increase in [Ca2+]i with a time course showing the highest value at the earliest measured time point, i.e. 40 s after exposure to the hyposmotic media and a subsequent decline towards the basal level during the following 320 s. The response in the cortical neurons was larger than in the granule cells but both types of neurons exhibited a similar increase in [Ca2+]i after exposure to 50 mM K+ which was of the same magnitude as the increase in [Ca2+]i observed in the cortical neurons exposed for 40 s to a medium with a 50% reduction in osmolarity. In both types of neurons the blocker of voltage gated Ca2+ channels verapamil had no effect on the hyposmolarity induced increase in [Ca2+]i. On the contrary, this increase in [Ca2+]i was dependent upon external calcium and could be inhibited partly or completely by the inorganic blockers of Ca2+ channels Mg2+ and La3+. Dantrolene which prevents release of Ca2+ from internal stores had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Sánchez-Olea
R
R
Department of Neurosciences, National University of Mexico, D.F.
Pasantes-Morales
H
H
Schousboe
A
A
D000814:Aniline Compounds; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002614:Chelating Agents; D003620:Dantrolene / Q000494:pharmacology*; D005260:Female; D005456:Fluorescent Dyes; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009997:Osmotic Pressure; D011247:Pregnancy; D014966:Xanthenes
D000814:Aniline Compounds; D002121:Calcium Channel Blockers; D002614:Chelating Agents; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D003620:Dantrolene; D002118:Calcium