0100488936

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THE IRREVERSIBLE INHIBITORY EFFECTS OF DIBENAMINE ON THE NORADRENALINE-, K- AND Ba-INDUCED CONTRACTIONS OF RAT'S ISOLATED VAS DEFERENS, PARTICULARLY IN RELATION TO Ca

English (英語)

The Kobe journal of the medical sciences

22(3)

139-151

1976-09

Actions of dibenamine (DB) on the adrenergic receptor site and the non-receptor sites were investigated in relation to Ca in the isolated rat vas deferens by an observation of its effect on the contractile responses to noradrenaline (NA), potassium (K) and barium (Ba). In this preparation, contractile responses to NA, K and Ba are all initiated by the release and influx of Ca, although a direct stimulation to the contractile elements of muscle is partially concerned with the Ba-induced contraction. Storage sites of Ca in the cell membrane are distinguished into three divisions, the first, the second and the third, which contains loosely-, less loosely- and tightly-bound Ca, respectively. K releases Ca from the first, NA releases Ca from the second and Ba releases Ca from all of the three divisions to elicit contraction. DB inhibited irreversibly the contraction by NA in high preference to that by K or Ba. Against DB-induced irreversible inhibition, the NA-contration was selectively protected by a high concentration of NA or tolazoline, whereas the K- and Ba-contractions were selectively protected by a high concentration of Ca. Contractile response to Ba initiated at 3 min after the removal of Ca from bath media was irreversibly potentiated by a low concentration but irreversibly reduced by a high concentration of DB. In addition, contractile response to K in the same condition was irreversibly reduced by DB. Contractile response to exogenous Ca on assistance with K in Ca-free media was also reduced irreversibly by DB. On the other hand, the residual contraction by Ba in Ca-free media, which is due to a direct stimulation to the muscle contractile element, was not modified by the treatment with DB. From these results, it is suggested that the irreversible inhibition by DB on the contractile response to NA may be due to the blockade of a-adrenergic receptor, whereas the irreversible inhibition by DB on the contractile responses to K and Ba may be attributable to the interference with the release and influx of Ca, although the release of Ca induced by Ba may be irreversibly accelerated by a low concentration of DB, and that the influence of DB on the muscle contractile elements may be ruled out. Discussion was made about the irreversible effect of DB on the NA-, K- and Ba-contrations analysed by the concentration-action curve.

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