Excitatory pathways in smooth muscle investigated by phase-plot analysis of isometric force development

Excitatory pathways in the smooth muscle of the pig urinary bladder were investigated using phase-plot analysis of isometric contractions. The phase plots, plots of the rate of change of the force as a function of the force itself, were dominated by a straight line described by the horizontal interc...

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Bibliographic Details
Published inThe American journal of physiology Vol. 261; no. 1 Pt 2; p. R138
Main Authors Van Koeveringe, G A, Van Mastrigt, R
Format Journal Article
LanguageEnglish
Published United States 01.07.1991
Subjects
Animals
Electric Stimulation
Isometric Contraction
Models, Neurological
Muscle, Smooth - innervation
Stimulation, Chemical
Swine
Urinary Bladder
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Summary:Excitatory pathways in the smooth muscle of the pig urinary bladder were investigated using phase-plot analysis of isometric contractions. The phase plots, plots of the rate of change of the force as a function of the force itself, were dominated by a straight line described by the horizontal intercept (Fiso) and the vertical intercept (U). The quotient Fiso/U is a time constant that characterizes the rate-limiting step in isometric force development in the muscle. Bladder strips of 1 mm diameter were activated by electrical field stimuli, acetylcholine, potassium, and ATP in combination with selective pathway inhibitors such as verapamil, atropine, or a calcium-free solution containing ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. When pathways that depended significantly on depolarization or intracellular calcium release were selected, the time constant was significantly smaller, indicating a faster process. The results indicated that the rate-limiting step in force development was determined by the influx of extracellular calcium.
ISSN:0002-9513
DOI:10.1152/ajpregu.1991.261.1.R138