The lab is studying how various G-protein-coupled receptors modulate the functional properties of (mostly) N-type calcium channels in rat sympathetic neurons. The goals are two-fold; by understanding the regulation of these channels in sympathetic neurons, we may understand better 1) how blood pressure is controlled, and 2) how presynaptic N-type calcium channels control the release of neurotransmitter in the brain. At least five different pathways which are thought to utilize differ-ent G-proteins affect these channels. Noradrenergic receptors of the alpha(1) subtype utilize a pertussis toxin(PTX)-sensitive G-protein to inhibit the N-type calcium channels via a membrane-delimited (and possibly direct; i.e., without the involvement of cytoplasmic second messengers) pathway. We have discovered that if the calcium-calmodulin regulated phosphatase calcineurin (CaN) is inhibited, the ability of the selective alpha(2) receptor agonist UK14304 to inhibit the calcium channels decreases by half. This effect is very significant for sympathetic neurons as the decrease in the alpha(2)-induced inhibitory response by CaN inhibition would lead to hyperactivity of these neurons. This mechanism could also explain why CaN inhibition when utilizing immunosuppressant drugs such as cyclosporine (a CaN inhibitor) leads to enhanced glutamate release and possibly neurotoxicity in the brain. We have also greatly expanded the knowledge base for the (as yet unknown) G-protein pathway coupled to m1 muscarinic receptors. This pathway does involve a cytoplasmic calcium-dependent component that we and others have yet to discover. During our studies, we have ruled out protein kinase C, calcin-eurin, and myosin light chain kinase. In addition we have provided clearer evidence of a G-protein distinct from the PTX type, and which inhibits the calcium channels in a mechanistically different way. We have also shown that a nearly identical G-protein pathway is responsible for the muscarinic receptor-induced inhibition of L-type calcium channels in pancreatic B cells.
