Mechanism of the Contracting Actions of K, Acetylcholine, Histamine, Noradrenaline and Ba in the Excised Vas Deferens of Guinea Pig, Particularly in Relation to Ca

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Using the strip of vas deferens from guinea pigs, the contractile mechansims of K, acetylcholine (ACh), histamine (Hist), noradrnaline (NA) and Ba, and the effects of the modified contents of Na and K in the bathing solution (BS) on the actions of these agents were investigated with respect to the mobilization of Ca. I. Actions of Contractile Drugs. 1. Shapes of the contractile responses to K, NA and Ba recorded on the smoked paper consisted of the phasic contraction (PC) and the subsequent tonic contraction (TC), whereas those to ACh and Hist showed only PC. PCs by these drugs are induced by the release of Ca from the storage sites. TCs by K and Ba are maintained by the energy-dependent active influx of Ca, whereas TC by NA is maintained by the release of Ca. Furthermore, since the contraction by Ba could be kept constant in Ca-free bath solution, it is conceivable that the direct stimulation of muscle contractile elements without the mediation of Ca mobilization is partly involved in the contracting mechanism of Ba. 2. In the muscle cell membrane, there are three divisions with Ca stores : the first is the store where Ca is most easily released, the second is where Ca is comparatively easily released, and the third is where Ca is not easily released. K and Hist can release Ca from the first store, ACh and NA from the first and second stores, and Ba from these three stores for producing the contraction. 3. Contractions induced by exogenous Ca in Ca-free bath solution are produced by the passive Ca-influx in the low Ca concentrations and by the additional active Ca-influx in the high Ca concentrations. II. Effect of the Modified Contents of Na in Bath Solution. 1. Removal of Na from the bath solution produced a sustained contraction through the release and the influx of Ca. 2. The facts that after 5 min exposure of the strip to Na-deficient solution, PCs by ACh, K and Ba and TCs by K and Ba were potentiated, suggest that the release and the influx of Ca by these agents are accelerated in the Na-deficient solution. However the facts that after 30 min exposure, PC by ACh and TCs by K and Ba were decreased, suggest that the release and the influx of Ca by these agents are subsequently inhibited. 3. Contractions by exogenous Ca in Ca-free solution increased at 5 min and 30 min but decreased at 120 min, after removal of Na from the solution. This finding indicates that the influx of Ca is accelerated and then inhibited. III. Effect of the Removal of K from Bath Solution. 1. After 30 min exposure of the preparation to K-free solution, PC by ACh and PC and TC by Ba were reduced. These findings suggest that the release and the influx of Ca due to these agents are inhibited by the exposure to K free solution 2. Contraction by exogenous Ca in the high concentration was more strongly reduced than in the low concentration by the exposure to K-free solution. Thus, it is considered that in the absence of external K, the active influx of Ca is more preferentially reduced than the passive influx of Ca.
近畿大学の論文
1976-12-28

Mechanism of the Contracting Actions of K, Acetylcholine, Histamine, Noradrenaline and Ba in the Excised Vas Deferens of Guinea Pig, Particularly in Relation to Ca

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