Factors affecting high-potassium-induced contracture of guinea-pig vas deferens.

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Abstract
Some factors which may influence the high-K-induced contracture of guinea-pig vas deferens were studied. Portional variations were observed in the height of tonic contraction but not in phasic contraction; tonic contraction was higher on the epididymal side and lower on the prostatic side. Circular muscle showed contracture similar to that of longitudinal muscle in the shapes of the contrature and the tendency to portional variations. Histological variations of muscle structure could not explain these variations. Electrical stimulation of the preparation by continuous weak AC current induced contracture similar to the high-K-induced contracture. The contracture evoked by AC stimulation was blocked by TTX [tetrodotoxin] and phentolamine. Blocking agents of possible transmission involved in high-K depolarization did not alter the relation of phasic and tonic contractions, although some of the drugs showed an inhibiting and some an enhancing effect. In isotonic observations, tonic contraction was highly sensitive to load and was elevated with a low load and depressed with a high load. The phasic and tonic contraction of high-K-induced contracture was a direct reaction of longitudinal muscle, although various factors could have had some influence on the contracture.