CALCIUM CHANNELS RESPONSIBLE FOR STRIATAL INHIBITORY TRANSMISSION. F. Tecuapetla, J.N. Guzman, L. Carrillo-Reid, D. Tapia, J. Bargas, E. Galarraga*. Instituto de Fisiologia Celular UNAM PO Box 70-253, Mexico City. Voltage-dependent Ca channels as P/Q and N types mediate transmitter release during synaptic transmission. Evoked GABAergic postsynaptic currents (eIPSCs) were recorded on spiny neurons using the whole-cell voltage-clamp technique. Previous work (Guzman et al, SFN 2002) has shown that eIPSCs in response to intrastriatal stimulation mainly come from interneurons whereas those evoked by antidromic stimulation from the pallidum come from axon collaterals that interconnect spiny cells. The P/Q-type Ca channel antagonist, agatoxin TK (400 nM), blocked most eIPSCs coming from both interneurons (90%) and axon collaterals (95%), whereas the N-type calcium channel antagonist, conotoxin GVIA (1 microM), only produced a partial block of all eIPSCs. It blocked 70% of axon collaterals eIPSCs, whereas eIPSCs f...