Effects of T-type, L-type, N-type, P-type, and Q-type calcium channel blockers on stimulus-induced pre-and postsynaptic calcium fluxes in rat hippocampal slices |
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Authors: | P Igelmund Y Q Zhao U Heinemann |
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Institution: | (1) Institut für Neurophysiologie, Universität zu Köln, Robert-Koch-Str. 39, D-50931 Köln, Germany;(2) Present address: Institut für Physiologie der Charité, Tucholskystr. 2, D-10117 Berlin, Germany |
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Abstract: | The contribution of T-, L-, N-, P-, and Q-type Ca2+ channels to pre-and postsynaptic Ca2+ entry during stimulus-induced high neuronal activity in area CA1 of rat hippocampal slices was investigated by measuring the effect of specific blockers on stimulus-induced decreases in extracellular Ca2+ concentration (Ca2+]0). Ca2+]0 was measured with ion-selective electrodes in stratum radiatum (SR) and stratum pyramidale (SP), while Ca2+ entry into neurons was induced with stimulus trains (20 Hz for 10 s) alternately delivered to SR and the alveus, respectively. The Ca2+]0 decreases recorded in SR in response to SR stimulation represented mainly presynaptic Ca2+ entry (Capre), while Ca2+]0 decreases recorded in SP in response to alvear stimulation were predominantly based on postsynaptic Ca2+ entry (Capost). Ethosuximide and trimethadione were ineffective m concentrations up to 1 mM. At 10 mM, they reduced Capost and, much less, also Capre Nimodipine (25 M) reduced Capost and, to a minor extent, Capre. -Agatoxin IVA (0.4–1 M) and -conotoxin MVIIC (1 M) also reduced both Capre and Capost, but with a stronger action on Capre. -Conotoxin GVIA (3–8 M) reduced Capost without effect on Capre. We conclude that during stimulus-induced, high-frequency neuronal activity Capost is carried by P/Q-, N-, and L-type channels and probably a further channel type different from these channels. Capre includes at least P/Q-and possibly L-type channels. N-type channels did not contribute to Capre in our experiments. Since ethosuximide and trimethadione were only effective in high concentrations, their action may be unspecific. Thus, T-type channels do not seem to play a major part in Ca2+ entry in this situation. |
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Keywords: | Calcium Hippocampal slice CA1 -Agatoxin IVA" target="_blank">gif" alt="ohgr" align="BASELINE" BORDER="0">-Agatoxin IVA -Conotoxin GVIA" target="_blank">gif" alt="ohgr" align="BASELINE" BORDER="0">-Conotoxin GVIA -Conotoxin" target="_blank">gif" alt="ohgr" align="BASELINE" BORDER="0">-Conotoxin MVIIC Nimodipine Ethosuximide Trimethadion Rat |
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