PHARMACOLOGICALLY DISTINCT PRESYNAPTIC CALCIUM CHANNELS IN CEREBELLAREXCITATORY AND INHIBITORY SYNAPSES

We have used whole-cell patch clamp recordings and pharmacological blo ckers of Ca channels to compare the pharmacology of Ca channels that m ediate synaptic transmission at the three types of synapses innervatin g Purkinje cells in rat cerebellar slices. Both parallel fiber and cli mbing fiber excitatory synapses were sensitive to the P-type Ca channe l blocker, omega-AgaIVA and the P/Q/N-type channel blocker, omega-cono toxin MVIIC. Transmission at inhibitory interneuronal synapses was not suppressed by these toxins, or by the N-type (omega-conotoxins GVIA a nd MVIIA) or L-type (nimodipine) channel blockers. Inhibitory transmis sion could be inhibited by Ni2+ and amiloride, but only at concentrati ons (IC50 similar to 300 mu M) that affect other types of Ca channels. These results indicate that excitatory and inhibitory presynaptic ter minals of the cerebellar cortex possess different types of voltage-gat ed Ca channels. The excitatory terminals contain P-type, Q-type and N- type Ca channels, with P-type channels playing the most prominent role . The inhibitory terminals possess quite different type(s) of Ca chann el. The heterogeneous distribution of Ca channel types should impart u nique properties to transmitter release from the excitatory and inhibi tory terminals. (C) 1997 Elsevier Science Ltd.