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 agonist.
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, omega-Conotoxin GVIA (omega-CgTx, 10-100 nM), significantly inhibited 3H-ACh release stimulated by 8Br-cAMP. 10 nM omega-CgTx also totally inhibited 8Br-cAMP-induced Ca++ efflux, whereas the L-type Ca++ channel blocker, nifedipine (1 microM), and the T-type Ca++ channel blocker, nickel (100 microM), 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).
Kojima
Y
Y
Department of Internal Medicine, The University of Michigan Medical Center, Ann Arbor 48109-0362, USA.
Tsunoda
Y
Y
Owyang
C
C
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D006168:Guinea Pigs; D007082:Ileum / Q000294:innervation; D008297:Male; D009197:Myenteric Plexus / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D010455:Peptides; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020866:omega-Conotoxin GVIA; D000242:Cyclic AMP; D000109:Acetylcholine; D002118:Calcium