Calcium channel density and hippocampal cell death with age in long- term culture

The expression of voltage-gated calcium (Ca²⁺) channel activity in brain cells is known to be important for several aspects of neuronal development. In addition, excessive Ca²⁺ influx has been linked clearly to neurotoxicity both in vivo and in vitro; however, the temporal relationship between the development of Ca²⁺ channel activity and neuronal survival is not understood. Over a period spanning 28 d in vitro, progressive increases in high voltage-activated whole-cell Ca²⁺ current and L-type Ca²⁺ channel activity were observed in cultured hippocampal neurons. On the basis of single-channel analyses, these increases seem to arise in part from a greater density of functionally available L-type Ca²⁺ channels. An increase in mRNA for the α₁ subunit of L-type Ca²⁺ channels occurred over a similar time course, which suggests that a change in gene expression may underlie the increased channel density. Parallel studies showed that hippocampal neuronal survival over 28 d was inversely related to increasing Ca²⁺ current density. Chronic treatment of hippocampal neurons with the L-type Ca²⁺ channel antagonist nimodipine significantly enhanced survival. Together, these results suggest that age-dependent increases in the density of Ca²⁺ channels might contribute significantly to declining viability of hippocampal neurons. The results also are analogous to patterns seen in neurons of aged animals and therefore raise the possibility that long-term primary neuronal culture could serve as a model for some aspects of aging changes in hippocampal Ca²⁺ channel function.