CALCIUM-CHANNEL TYPES CONTRIBUTING TO EXCITATORY AND INHIBITORY SYNAPTIC TRANSMISSION BETWEEN INDIVIDUAL HYPOTHALAMIC NEUTRONS

The contribution of L-, N-, P- and Q-type Ca2+ channels to excitatory and inhibitory synaptic transmission and to whole-cell Ba2+ currents t hrough Ca2+ channels (Ba2+ currents) was investigated in rat hypothala mic neurons grown in dissociated cell culture. Excitatory and inhibito ry postsynaptic currents (EPSCs and IPSCs) were evoked by stimulating individual neurons under whole-cell patch-clamp conditions. The differ ent types of high-voltage-activated (HVA) Ca2+ channels were identifie d using nifedipine, omega-Conus geographus toxin VIA (omega-CTx GVIA), omega-Agelenopsis aperta toxin IVA (omega-Aga IVA), and omega-Conus m agus toxin VIIC (omega-CTx MVIIC). N-, but not P- or Q-type Ca2+ chann els contributed to excitatory as well as inhibitory synaptic transmiss ion together with Ca2+ channels resistant to the aforementioned Ca2+ c hannel blockers (resistant Ca2+ channels). Reduction of postsynaptic c urrent (PSC) amplitudes by N-type Ca2+ channel blockers was significan tly stronger for IPSCs than for EPSCs. In most neurons whole-cell Ba2 currents were carried by L-type Ca2+ channels and by at least two oth er Ca2+ channel types, one of which is probably of the Q-type and the others are resistant Ca2+ channels. These results indicate a different contribution of the various Ca2+ channel types to excitatory and inhi bitory synaptic transmission and to whole-cell currents in these neuro ns and suggest different functional roles for the distinct Ca2+ channe l types.