Effects of Mn, Zn and Mg Ions on the Electrical Activities of Smooth Muscle of Guinea-pig Taenia Coli

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The effects of Nn, Zn and Mg ions on the membrane potential and contraction of the smooth muscle from the guinea-pig taenia coli were investigated. The simultaneous recording of electrical and mechanical activities was performed using the sucrose-gap method and a mechano-electric transducer.<br> Mn ions depressed spontaneous spike discharge without changing the membrane potential, and also perfectly depressed the spontaneous contraction. These effects of Mn ions were reversible. Mn ions competed with Ca ions in the spike discharge and contraction. The effects of Zn ions on the spontaneous spike discharge and contraction were similar to those of Mn ions, but they were irrever-sible. Mg ions at a high concentration depressed the spontaneous spike discharge, but did not influence the membrane potential. Reduction or lack of Mg ions induced an increase of spontaneous spike discharge. In media of high Mn or Zn, electrical stimulation was effective in eliciting the spike potential but failed to induce tension development.<br> Such a dissociation between electrical and mechanical activities was also confirmed by KCl- and ACh-depolarization in media of high Mn or Zn. KCl-depolarizations without tension development were observed in high Mn and Zn media. ACh-depolarization without tension development was observed in high Mn media, but neither depolarization nor tension development was observed in high Zn media.<br> Mg did not exert a suppressive effect on the KCl- or ACh-depolarization and contracture.

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