Contributions of multiple calcium channel types to GABAergic transmission in rat cultured hippocampal neurons.

Effects of Ca2+ channel blockers on GABAergic transmission were examined with rat cultured hippocampal neurons. The GABAergic synaptic currents (IPSCs) evoked by electrical stimulation of single presynaptic neurons were recorded from voltage-clamped postsynaptic neurons. The amplitude of IPSCs was not changed by 10 microM nifedipine (L-type Ca2+ channel blocker), but was decreased irreversibly to 37% of control by 1 microM omega-conotoxin GVIA (N-type blocker, CgTX), to 67% by 0.1 microM omega-agatoxin IVA (P-type blocker, AGTX), and to 1% by both toxins. From these data and the Ca(2+)-dependence of IPSCs, the contributions of CgTX-sensitive and AGTX-sensitive Ca2+ channels to the transmission were estimated at 59% and 36%, respectively.