Disturbances in rat smooth-muscle induced by a substance with fungicide action

The fungicide substance QAS [N,N,N',N'-tetramethyl-N,N'-di(8,15-dichloropentadeca-5,10- dien)ethylenediamine methylsulphate] has a biphasic effect on the spontaneous electrical and mechanical activity of smooth-muscle samples of rat corpus and guinea-pig taenia coli. During the first phase of QAS application membrane depolarization and increased spontaneous spike frequency were recorded. The tone of the preparations (resting tone) increased transiently. Calcium ion-entry blockers did not affect the contractile effect of QAS, but K(+)-channel blockers and some modulators of the second messenger system abolished or decreased it. During the second phase depolarization increased progressively, spike frequency decreased and the increase in resting tone recorded during the first phase was eliminated. The results reveal that the long-lasting depolarizing effect of QAS (in concentrations used for plant protection) probably inactivates the entry of Ca2+ into the smooth-muscle cells and disturbs Ca2+ homeostasis.