Activity of voltage-operated calcium channels in rat cerebellar granule neurons and neuronal survival.

Neuronal activity and Ca2+ channel activation play important roles in neuronal survival and development. In cerebellar granule neurons, the culture conditions can induce differential expression of various membrane receptor proteins. To test the hypothesis that culture conditions might affect the activity of voltage-operated Ca2+ channels, the present study analysed the differences in Ca2+ signalling between granule neurons grown in the presence of normal (5 mM) or high (25 mM) KCl. The Ca2+ transients evoked by 50 mM KCl developed similarly in both cultures, as a function of age. In contrast, when compared with neurons grown in 25 mM KCl, a proportion of the neurons grown in normal KCl showed, between days in vitro 4 and 6, a higher Ca2+ transient in response to 12.5 mM KCl. These neurons were less sensitive to the effect of 10 microM nifedipine and, conversely, more sensitive to the effects of 10 microM omega-conotoxin MVIIC when stimulated with 50 mM KCl, indicating that they express preferentially, at this stage, the N- and/or Q-type Ca2+ channels. This period of maximal activity of the N/Q-type Ca2+ channels was associated with a significant increase in the rate of neuronal apoptosis. The present study also shows, by comparing the rates of neuronal apoptosis, that the long-term maintenance in 25 mM KCl appears to "synchronize" and sensitize the neuronal population to the apoptotic process. These results illustrate the differential effect the culture conditions can have on the expression and activity of Ca2+ channels, which, in turn, can modulate neuronal survival.