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Dissociation between electrical and mechanical responses to nitrergic stimulation in the canine gastric fundus
Author(s) -
Bayguinov Orline,
Sanders Kenton M.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.437bn.x
Subject(s) - chemistry , hyperpolarization (physics) , stimulation , endocrinology , membrane potential , medicine , sodium nitroprusside , biophysics , inhibitory postsynaptic potential , nitric oxide , biochemistry , biology , stereochemistry , organic chemistry , nuclear magnetic resonance spectroscopy
1 We examined the relationships between membrane potential, intracellular [Ca 2+ ] ([Ca 2+ ] i ), and tension in muscles of the canine gastric fundus in response to nitrergic stimulation by NO donors and electrical field stimulation (EFS) of intrinsic enteric inhibitory neurons when adrenergic and cholinergic responses were blocked. 2 NO donors reduced [Ca 2+ ] i and tension in a concentration‐dependent manner. A close relationship was noted between these parameters. 3 In terms of the [Ca 2+ ] vs. force relationship, relaxation responses to EFS differed from responses to NO donors. EFS resulted in smaller decreases in [Ca 2+ ] i to produce a given relaxation compared with responses to NO donors. Thus, muscles stimulated with EFS were less sensitive to [Ca 2+ ] i than muscles stimulated with exogenous NO. 4 When membrane potential, [Ca 2+ ] i and tension were monitored simultaneously in the same muscles, a temporal dissociation was noted between the electrical responses and changes in [Ca 2+ ] i and tension. Brief electrical responses were associated with more sustained changes in [Ca 2+ ] i and tension. 5 Further dissociation between electrical and mechanical effects was noted. Changes in [Ca 2+ ] i and tension caused by sodium nitroprusside and EFS were blocked by arginine analogues and by oxyhaemoglobin, but electrical responses were unaffected. 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ), an inhibitor of soluble guanylyl cyclase, also blocked the effects of nitrergic stimulation on [Ca 2+ ] i and tension, without affecting hyperpolarization. Thus, in the presence of continued hyperpolarization, the reductions in [Ca 2+ ] i and tension caused by nitrergic stimulation were blocked. 6 Block of hyperpolarization in response to nitrergic stimulation with tetrapentylammonium chloride (TPEA) had relatively little effect on the [Ca 2+ ] i and tension responses. Thus, hyperpolarization is not required for nitrergic effects on [Ca 2+ ] i and tension. 7 In summary, reduction in [Ca 2+ ] i and tension in response to nitrergic stimulation of the canine gastric fundus does not depend upon electrical hyperpolarization. Non‐electrical mechanisms such as enhanced uptake of Ca 2+ by the sarcoplasmic reticulum or reduction in the Ca 2+ sensitivity of the contractile apparatus may be the primary mechanisms mediating nitrergic responses in these muscles.