Vol. 282, Issue 1, 403-409, 1997

Adenosine 3,5-Cyclic Monophosphate-Stimulated Ca⁺⁺ Efflux and Acetylcholine Release in Ileal Myenteric Plexus Are Mediated by N-Type Ca⁺⁺ Channels: Inhibition by the Kappa Opioid Receptor Agonist¹

Yuichiro Kojima, Yasuhiro Tsunoda and Chung Owyang

Department of Internal Medicine, The University of Michigan Medical Center, Ann Arbor, Michigan

Adenosine 3,5-cyclic monophosphate (cAMP) is an important second messenger involved in cholinergic transmission. The aims of this study were to characterize the calcium channels associated with cyclic AMP-mediated acetylcholine release and Ca⁺⁺ efflux in ileal myenteric plexus. We also examined if this process can be inhibited by agents such as opioids that inhibit N-type calcium channels via a pertussis toxin-sensitive G protein. Application of a cell permeant analogue, 8-bromoadenosine cyclic AMP (8Br-cAMP) (1 mM), and an activator of the adenylyl cyclase system, forskolin (0.1 mM), in a superfusion system resulted in both Ca⁺⁺ efflux and ³H-acetylcholine (ACh) release from the dispersed myenteric ganglia. A preferential N-type Ca⁺⁺ channel blocker, -Conotoxin GVIA (-CgTx, 10-100 nM), significantly inhibited ³H-ACh release stimulated by 8Br-cAMP. 10 nM -CgTx also totally inhibited 8Br-cAMP-induced Ca⁺⁺ efflux, whereas the L-type Ca⁺⁺ channel blocker, nifedipine (1 µM), and the T-type Ca⁺⁺ channel blocker, nickel (100 µM), both had no effects on the action of 8Br-cAMP. ³H-ACh release during 0.1 mM forskolin stimulation was inhibited by pretreatment with a kappa receptor agonist, U50488H at 1 to 100 nM. In addition, U50488H significantly inhibited ³H-Ach release and Ca⁺⁺ efflux elicited by 8Br-cAMP. Inhibition of ³H-ACh release by U50488H was reversed by 3 hr pretreatment with 300 ng/ml pertussis toxin. These results suggest that, in the myenteric plexus, cyclic AMP-stimulated Ca⁺⁺ efflux and Ach release were mediated by N-type calcium channels. This process may be inhibited by activation of the kappa opioid receptor through pertussis toxin-sensitive G protein(s).