Calcium requirement for cgmp production during muscarinic.
Thompson, Stuart H., Chris Mathes, and Adawia A. Alousi.
Department of Biological Sciences, and the Hopkins Marine Station,
Stanford University, Pacific Grove, CA 93950
APStracts 2:0186C, 1995.
Muscarinic agonists elicit large increases in intracellular Ca2+ and
cGMP in N1E-115 neuroblastoma cells. Both signals are blocked in
cells loaded with the Ca2+ buffer BAPTA showing that the increase in
(Ca)i is necessary to stimulate cGMP accumulation. Inhibition of
nitric oxide synthase blocks the cGMP response without affecting the
peak amplitude of the (Ca)i signal and it is concluded that Ca2+
-dependent activation of NO-synthase is required for cGMP production.
cGMP accumulation is reduced by 60% when cells are bathed in Ca2+
-free saline but the peak change in (Ca)i is not affected. This
suggests that Ca2+ influx is strongly coupled to the activation of
cGMP production even though it makes a smaller contribution to the
intracellular Ca2+ signal than does Ca2+ release. Thapsigargin, which
releases Ca2+ from intracellular stores, activates Ca2+ influx and
increases cGMP. The cGMP increase is transient and follows
approximately the same time course as Ca2+ store depletion. Ca2+
influx remains activated after store depletion, however, which
indicates that influx alone cannot sustain cGMP production. It is
concluded that summation of Ca2+ influx and Ca2+ release is necessary
to reach a threshold Ca2+ level needed to stimulate cGMP
accumulation. Because of the large contribution from Ca2+ influx, we
suggest that NO-synthase or a co-factor necessary for its activation
may be located close to Ca2+ channels in the membrane.
Received 4 November 1994; accepted in final form 28 March 1995.
APS Manuscript Number C660-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.