DISTINCT, CONVERGENT 2ND MESSENGER PATHWAYS MODULATE NEURONAL CALCIUMCURRENTS

Norepinephrine (NE) and gamma-aminobutyric acid (GABA) inhibit N-type calcium channels in embryonic chick sensory neurons. We demonstrate he re that the modulatory actions of the two transmitters are mediated th rough distinct biochemical pathways. Intracellular application of the pseudosubstrate inhibitor for protein kinase C blocks the inhibition p roduced by NE (and the protein kinase C activator oleoylacetylglycerol ), but not that produced by GABA. Calcium current inhibition produced by oleoylacetylglycerol occludes inhibition by subsequent application of NE; GABA-mediated inhibition, however, is not eliminated by prior a ctivation of protein kinase C. These results demonstrate that multiple biochemical pathways converge to control N-type calcium channel funct ion.