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IRREVERSIBLE INHIBITORY EFFECT OF ATROPINE ON THE CONTRACTILE RESPONSES TO DRUGS IN ISOLATED RAT RECTUM, PARTICULARLY IN RELATION TO Ca

English (英語)

The Kobe journal of the medical sciences

22(4)

239-246

1976-12

Effect of atropine sulfate (atropine) on the contractile responses to acetylcholine chloride (ACh) and potassium chloride (K) was investigated in isolated rat rectum. The tension of the strips suspended in the bath medium (Locke solution, 30° C) was isotonically recorded. The K (ED50)-induced contraction was not affected by atropine at 1.5 x 10^-3 mM, which reversibly abolished the ACh (ED100)-contraction. After washout of 6.0 x 10^- 3 mM atropine, the phasic, but not the tonic, component of ACh (ED50) - and K (ED50) -contractions were to some extent inhibited irreversibly. However, such irreversible inhibition of the phassic component was not produced by the atropine methylbromide even in the high concentration of 3.0 X 10^- 2 mM. The irreversible inhibition by atropine of 6.0 X 10^-3 mM on the phasic component of K-contraction was protected by pretreatment with a high concentration of ACh or K. In addition, these irreversible inhibition by atropine was potentiated by the absence of Ca and was abolished by the increase of Ca content in bath media. In preparations in which the irreversible inhibitory effect of atropine is obtained, K-contraction at about 3 min after the removal of Ca from bath medium was significantly reduced. However, contraction by exogenous Ca in high K-depolarizing Ca-free bath media was affected neither by the combined treatment nor by the incubation with atropine. These results suggest that the irreversible inhibition of the contractile responses to drugs by atropine in high concentrations may be due to the interference with the release of Ca in the deep layer of the membrane, rather than by a blockade of muscarinic receptor sites.

influx of Ca

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