Protein Kinase C Is Involved in M1-Muscarinic Receptor-Mediated Facilitation of L-Type Ca2+ Channels in Neurons of the Major Pelvic Ganglion of the Adult Male Rat

We used patch clamp recording techniques to determine if muscarinic signaling mechanisms are present in dissociated autonomic neurons obtained from the major pelvic ganglion, which provides the cholinergic innervation of the urinary bladder and other pelvic organs. The M₁ specific agonist, McN-A-343 (2–30 M) enhanced Ca²⁺ currents in approximately 37% of neurons (by 50–80%). This enhancement was reduced by atropine (5–10 M) or a PKC inhibitor (bisindolylmaleimide, 50–200 nM). In responsive neurons Ca²⁺ currents were also enhanced by the phorbol ester, phorbol-12, 13-dibutyrate (50–300 nM) and the dihydropyridine agonist Bay K 8644 (5 M) and had kinetics of activation and inactivation as expected for L-type Ca²⁺ channels. We conclude that in a subpopulation of MPG neurons, M₁-mediated activation of PKC phosphorylates and enhances L-type Ca²⁺ channel activities. This muscarinic facilitatory mechanism in MPG neurons may be the same as the M₁-mediated facilitation of transmitter release reported previously at the nerve terminals in the urinary bladder.