DIFFERENTIAL REGULATION OF N-TYPE AND Q-TYPE CA2-NUCLEOTIDES AND G-PROTEINS( CHANNELS BY CYCLIC)

Voltage-dependent Ca2+ channels play a central role in controlling neu rotransmitter release at the synapse. They can be inhibited by certain G-protein-coupled receptors, acting by a pathway delimited to the mem brane. In addition, modulation of Ca2+ channel activity by protein kin ases also contributes to the dynamic regulation of neuronal physiology . Recently, differences in these modulations between Ca2+ channel subt ypes have been shown in several neuronal preparations. Here we show th at two types of presynaptic Ca2+ channel (N-type and Q-type) are diffe rentially regulated by cAMP and G-proteins using a Xenopus oocyte expr ession system. Treatment to increase cytosolic cAMP concentration with forskolin and 3-isobutyl-1-methylxanthine (IBMX) markedly potentiated Q-type channel current, and the enhancement was reversed by protein k inase A inhibitors. Much smaller enhancement was observed in N-type ch annel current after the cAMP elevation. When large depolarizing prepul se was applied to the oocytes for evaluation of the tonic inhibition o f Ca2+ channels by intrinsic G-protein activity, N-type channel curren t elicited a large prepulse facilitation but Q-type channels did not. The tonic inhibition of N-type channels was abolished by an intracellu lar perfusion with a 'cut-open' recording configuration, or by co-expr ession with G(alpha o). When kappa opioid receptors were co-expressed and stimulated with agonists, depolarization-resistant inhibition was more apparent in Q-type channels than in N-type channels. These result s suggest that Q-type channels are more susceptible to the protein kin ase A-mediated facilitation than N-type channels, and that activity of N-type channels can be more highly regulated in a voltage-dependent m anner by G(beta gamma) than that of Q-type channels. These differences may account for the selective regulation of neurotransmitter release by these Ca2+ channels.