Differential contribution of L-, N-, and P/Q-type calcium channels to [Ca2+]i changes evoked by kainate in hippocampal neurons.
We investigated the contribution of L-, N- and P/Q-type Ca(2+) channels to the [Ca(2+)](i) changes, evoked by kainate, in the cell bodies of hippocampal neurons, using a pharmacological approach and Ca(2+) imaging. Selective Ca(2+) channel blockers, namely nitrendipine, omega-Conotoxin GVIA (omega-GVIA) and omega-Agatoxin IVA (omega-AgaIVA) were used. The [Ca(2+)](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 Ca(2+) channel blocker caused differential inhibitory effects on [Ca(2+)](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 omega-GVIA or omega-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 omega-GVIA or omega-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 Ca(2+) channels activated by stimulation of the AMPA/kainate receptors.
Santiago
Ana R
AR
Center for Neuroscience and Cell Biology, Department of Zoology, University of Coimbra, Coimbra, 3004-517, Portugal.
Carvalho
Caetana M
CM
Carvalho
Arsélio P
AP
Ambrósio
António F
AF
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D020865:Calcium Channels, P-Type / Q000378:metabolism*; D020907:Calcium Channels, Q-Type / Q000378:metabolism*; D002478:Cells, Cultured; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007608:Kainic Acid / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009568:Nitrendipine / Q000378:metabolism; D011810:Quinoxalines / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020867:omega-Agatoxin IVA / Q000378:metabolism; D020866:omega-Conotoxin GVIA / Q000378:metabolism
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D011810:Quinoxalines; D020867:omega-Agatoxin IVA; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D020866:omega-Conotoxin GVIA; D009568:Nitrendipine; D007608:Kainic Acid; D002118:Calcium