Extracellular atp mediates calcium signaling in cultured myenteric
neurons via a phospholipase c-dependent mechanism.
Kimball, Beth C., David I. Yule, Michael W. Mulholland.
Departments of Surgery and Physiology, University of Michigan, Ann
Arbor, Michigan, 48109
APStracts 2:0227G, 1995.
In the myenteric plexus, ATP is released as a neurotransmitter by
'purinergic' nerves, relaxing visceral smooth muscle. We report a
signal transduction mechanism for ATP in cultured myenteric neurons
involving receptor-mediated release of intracellular calcium stores.
Primary cultures of myenteric neurons from guinea pig taenia coli
were loaded with the calcium indicator fura-2/AM and examined using
digital imaging microscopy. Superfusion of single neurons with ATP
(0.01 - 1000 [mu]M) resulted in concentration-dependent increases in
[Ca2+]i which were independent of extracellular calcium. Decrements
in peak [Ca2+]i were seen with repetitive ATP exposure.
Responsiveness of myenteric neurons to purinergic agonists (100
[mu]M) was consistent with action at a neuronal P2y purinoceptor: 2
-chloro-ATP = ATP = 2-MeSATP > ADP > a,b-MeATP = b,g-MeATP
> AMP > adenosine. ATP-evoked calcium transients were
inhibited dose-dependently by suramin, a non-specific P2 antagonist,
and reactive blue 2, a specific P2y antagonist. ATP and cyclopiazonic
acid (30 [mu]M) appear to release an identical intracellular calcium
store. Pre-incubation with the aminosteroid U-73122 (10 [mu]M)
inhibited ATP-evoked calcium transients by 71+7 % while phorbol ester
pre-treatment (PMA, 100 nM, 5 min.) caused a 76+4 % inhibition. Peak
[Ca2+]i evoked by ATP was not affected by pre-incubation with
pertussis toxin (100 ng/ml, 24 hrs.) or nifedipine (10 [mu]M). These
data suggest a signal transduction mechanism for ATP in cultured
myenteric neurons involving purinoceptor-mediated activation of
phospholipase C, with release of IP3-sensitive intracellular calcium
stores.
Received 13 January 1995; accepted in final form 9 October 1995.
APS Manuscript Number G18-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95