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Is co‐transmission involved in the excitatory responses of the rat anococcygeus muscle?
Author(s) -
Cunnane T.C.,
Muir T.C.,
Wardle Kay A.
Publication year - 1987
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1987.tb11293.x
Subject(s) - phentolamine , depolarization , prazosin , tetrodotoxin , excitatory postsynaptic potential , biophysics , chemistry , membrane potential , stimulation , muscle contraction , medicine , endocrinology , biology , receptor , antagonist , biochemistry
1 Electrical and mechanical responses to field (transmural) and extrinsic nerve stimulation were recorded simultaneously in the rat anococcygeus muscle. Membrane potential changes recorded intracellularly following either method of stimulation were indistinguishable. Single stimuli usually produced a slow depolarization; trains of pulses produced a fast excitatory junction potential (e.j.p.) initially, followed by a slow depolarization similar to that produced by single pulses. The fast e.j.ps, the slow depolarizations and the accompanying contractions were abolished by the α‐adrenoceptor antagonists, phentolamine (1 × 10 −6 m ) or prazosin (1 × 10 −7 m ) and by tetrodotoxin (TTX, 1 × 10 −6 m ) but unaffected by α, β‐methylene adenosine triphosphate (α, β‐MeATP, 1–10 × 10 −6 m ), an agent known to desensitize purinoceptors. 2 Application of noradrenaline (NA, 1 × 10 −8 ‐1 × 10 −6 m ), by pressure ejection from a micropipette, depolarized the membrane and produced a localized contraction, both of which were abolished by phentolamine (1 × 10 −6 m ) or prazosin (1 × 10 −7 m ). 3 Application of adenosine‐5′‐triphosphate (ATP, 1 × 10 −4 ‐1 × 10 −3 m ), by pressure ejection from a micropipette, produced a small membrane depolarization and localized contraction which were unaffected by phentolamine (1 × 10 −6 m ) or prazosin (1 × 10 −7 m ) but abolished by α, β‐MeATP (1 × 10 −6 m ). 4 The results show that, in the rat annococcygeus muscle, (1) field or extrinsic nerve stimulation released only one excitatory transmitter, namely NA, although receptors for both NA and ATP were present on the muscle, (2) α, β‐MeATP was selective for purinoceptors and (3) there was no evidence for excitatory co‐transmission in this tissue.