ACTIVATION OF ADENOSINE A(1) AND A(2) RECEPTORS DIFFERENTIALLY MODULATES CALCIUM CHANNELS AND GLYCINERGIC SYNAPTIC TRANSMISSION IN RAT BRAIN-STEM

Multiple types of calcium channels are responsible for calcium influx that triggers transmitter release in the mammalian CNS. To test the co ntribution of each calcium channel type an synaptic modulation, we rec orded calcium currents from somata of presynaptic interneurons and uni tary glycinergic postsynaptic currents in the rat brainstem. In intern euron somata, A(1) receptor activation inhibited predominantly N-type (omega-conotoxin GVIA-sensitive) and, to a lesser extent, P-type (omeg a-agatoxin IVA-sensitive) channels. At the presynaptic terminal N- and P-type channels mediated synaptic transmission. omega-CgTx occluded s ynaptic inhibition by A(1) receptor activation, suggesting that synapt ic inhibition was mediated predominantly by N-type channel inhibition. A(2) receptor activation facilitated synaptic transmission, probably through potentiation of P-type channels at the presynaptic terminal.