Acetylcholine increases intracellular calcium of arterial chemoreceptor
cells of adult cats.
Machiko Shirahata, Robert S Fitzgerald, and James S.K.Sham.
Departments of Environmental Health Sciences, Anesthesiology/Critical Care
Medicine, Physiology and Medicine, The Johns Hopkins Medical Institutions, 615
N. Wolfe Street, Baltimore, MD 21205
APStracts 4:154N, 1997.
ABSTRACT
Several neurotransmitters have been reported to play important roles in the
chemoreception of the carotid body. Among them acetylcholine (ACh) appears to
be involved in excitatory processes in the cat carotid body. As one of the
steps to elucidate possible roles of ACh in carotid body chemoreception in the
cat we examined the effect of ACh on intracellular calcium concentration
([Ca2+]i) of cultured carotid body cells. The carotid body from adult cats was
dissociated and cultured for up to two weeks. [Ca2+]i was measured from
clusters of cells with a microfluorometric technique using Indo-1 AM.
Experiments were performed at 37 øC, and cells were continuously superfused
with modified Krebs solutions equilibrated with 5% CO2/16% O 2/79% N2. ACh
(100 æM) caused a marked increase in [Ca2+]i in approximately 70% of clusters,
and the responses to 1-300 æM of ACh were concentration-dependent. The
magnitude and kinetics of the ACh response were mimicked by the application of
nicotine, whereas muscarinic agonists, pilocarpine and muscarine, failed to
evoke a similar response. ACh-induced increase in [Ca2+]i was dependent on
extracellular Ca2+: It was greatly reduced or completely abolished by a
transient removal of extracellular Ca2+. The response was consistently but
only partially reduced by caffeine (5 mM) or nifedipine (10 æM). The effect of
mecamylamine (100 æM) was inhibitory, but small. Moreover, the increase in
[Ca2+]i in response to ACh was also observed in some clusters which did not
respond to high K (100 mM) Krebs. These results suggest that ACh increases
[Ca2+]i of cultured carotid body cells by activating neuronal nicotinic ACh
receptors, leading to Ca2+ influx via nicotinic channels. In addition, other
pathways such as Ca2+ influx through L-type calcium channels, perhaps
secondary to membrane depolarization, and Ca2+ release from intracellular
stores may participate in increasing [Ca2+]i in response to ACh. Muscarinic
receptors appear to play only a small role, if any.
Received 18 September 1996; accepted in final form 14 July 1997.
APS Manuscript Number J752-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 27 August 1997