A DIFFUSIBLE 2ND MESSENGER MEDIATES ONE OF THE PATHWAYS COUPLING RECEPTORS TO CALCIUM CHANNELS IN RAT SYMPATHETIC NEURONS

Muscarinic and alpha-adrenergic suppression of current through Ca2 channels was studied in adult rat superior cervical ganglion neurons using whole-cell and cell-attached configurations of the patch-clamp technique. Oxotremorine methiodide suppressed I(Ca) by both a rapid (<< 1 s) and a slow (> 4 s) process, whereas norepinephrine suppressed I(Ca) only by a rapid process. The slow muscarinic suppression could be prevented by adding 20 mM BAPTA, a Ca2+ chelator, to the recording pipette, whereas the adrenergic suppression was not affected. Muscarinic, but not alpha-adrenergic, receptors can couple to Ca2+ channels by a second messenger capable of diffusing into an on-cell patch. This signal seems not to be carried by intracellular Ca2+, cGMP, cAMP, or protein kinase C.