Role for diacylglycerol in mediating the actions of ACh on M-current in gastric smooth muscle cells.
The role of the second messenger diacylglycerol (DAG) in mediating muscarinic suppression of M-current, a type of a voltage-gated K+ current that is suppressed by acetylcholine (ACh), was examined in freshly isolated smooth muscle cells from toad stomach. Currents were recorded using a single electrode voltage clamp employing conventional microelectrodes. Extracellular application of 1,2-dioctanoyl-sn-glycerol (DiC8), a synthetic DAG that is a potent activator of protein kinase C (PKC), reversibly suppressed M-current. Current relaxations, representing the voltage-dependent closure of K+ channels underlying M-current, were also decreased by DiC8, although suppression was not always as complete as it was with ACh. In contrast, another DAG analogue, 1,2-dioctanoyl-3-thioglycerol, which has a structure closely related to DiC8 but does not activate PKC, failed to inhibit M-current. Furthermore, M-current induced by the beta-agonist isoproterenol, by a mechanism apparently mediated by adenosine 3',5'-cyclic monophosphate (S. M. Sims, L. H. Clapp, J. V. Walsh, Jr., and J. J. Singer. Pflugers Arch. 417: 291, 1990), was also suppressed by DiC8. Both ACh and DiC8 were found to suppress endogenous and isoproterenol-induced M-current without altering the time course of M-current deactivation, suggesting that these agents act by decreasing the number of channels available to be opened. These results provide evidence that muscarinic regulation of M-current is mediated by DAG.
Clapp
L H
LH
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
Sims
S M
SM
Singer
J J
JJ
Walsh
J V
JV
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002024:Bufo marinus; D004075:Diglycerides / Q000494:pharmacology / Q000502:physiology*; D004553:Electric Conductivity; D007545:Isoproterenol / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D013270:Stomach / Q000166:cytology / Q000187:drug effects* / Q000502:physiology
D004075:Diglycerides; C044295:1,2-dioctanoylglycerol; D007545:Isoproterenol; D000109:Acetylcholine