P- and R-type Ca2+ channels regulating spinal glycinergic nerve terminals.

The contributions of P- and R-type Ca2+ channels on glycinergic nerve endings (boutons) projecting to the rat spinal sacral commissural nucleus (SDCN) neurons are not understood. Thus, we investigated the functional role of P- and R-type Ca2+ channels by measuring the inhibitory postsynaptic currents (eIPSCs) evoked from individual nerve endings (boutons) by focal electrical stimulation. The current amplitude and failure rate (Rf) of glycinergic eIPSCs varied directly with changes in [Ca2+](o). Low concentration of omega-Aga IVA (P-type selective antagonist) suppressed eIPSCs as much as high concentration (both P- and Q-type selective) indicating little contribution of Q-type Ca2+ channels. Antagonism of R-type Ca2+ channels with SNX-482 and Ni2+ greatly decreased the current amplitude and increased failure rate (Rf) of glycinergic eIPSCs. Overall, our results suggest that the dominant control of glycine release depends on Ca2+ entry through P- and R-type Ca2+ channels that ubiquitously populate spinal glycine release sites.