Differential Contribution of L-, N-, and P/Q-type Calcium Channels to [Ca2+]i Changes Evoked by Kainate in Hippocampal Neurons

Abstract

Abstract We investigated the contribution of L-, N- and P/Q-type Ca2+ channels to the [Ca2+]i changes, evoked by kainate, in the cell bodies of hippocampal neurons, using a pharmacological approach and Ca2+ imaging. Selective Ca2+ channel blockers, namely nitrendipine, ?-Conotoxin GVIA (?-GVIA) and ?-Agatoxin IVA (?-AgaIVA) were used. The [Ca2+]i changes evoked by kainate presented a high variability, and were abolished by NBQX, a AMPA/kainate receptor antagonist, but the N-methyl-d-aspartate (NMDA) receptor antagonist, D-AP5, was without effect. Each Ca2+ channel blocker caused differential inhibitory effects on [Ca2+]i responses evoked by kainate. We grouped the neurons for each blocker in three subpopulations: (1) neurons with responses below 60% of the control; (2) neurons with responses between 60% and 90% of the control, and (3) neurons with responses above 90% of the control. The inhibition caused by nitrendipine was higher than the inhibition caused by ?-GVIA or ?-AgaIVA. Thus, in the presence of nitrendipine, the percentage of cells with responses below 60% of the control was 41%, whereas in the case of ?-GVIA or ?-AgaIVA the values were 9 or 17%, respectively. The results indicate that hippocampal neurons differ in what concerns their L-, N- and P/Q- type Ca2+ channels activated by stimulation of the AMPA/kainate receptors.