AJP - Cell Physiology, Vol 263, Issue 6 C1274-C1281, Copyright © 1992 by American Physiological Society
Role for diacylglycerol in mediating the actions of ACh on M-current in gastric smooth muscle cells
L. H. Clapp, S. M. Sims, J. J. Singer and J. V. Walsh Jr
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
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.
