EFFECTS OF DILTIAZEM ON ELECTRICAL AND MECHANICAL ACTIVITIES OF ISOLATED GUINEA PIG TAENIA COLI

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Abstract
Effects of diltiazem [a coronary vasodilator] on electrical and mechanical activities of isolated guinea pig tenia coli were studied by means of the double sucrose-gap method. In the spontaneously active preparations, diltiazem (2.2 .times. 10-6 M) suppressed both electrical activity and isometric contraction; electrical and mechanical activities evoked by the depolarizing current pulse were not affected at the concentration of 2.2 .times. 10-6 M. In the presence of 2.2 .times. 10-5 M diltiazem, the evoked contractile force and the number of repetitive firings during depolarization were reduced; the single spike was almost unchanged or somewhat inhibited. At 2.2 .times. 10-4 M diltiazem, both electrical and mechanical activities were almost abolished. The contractile force and single spike suppressed by diltiazem were partly reversed by the addition of 5 mM CaCl2. There was little significant change in membrane potential and resistance. Similar but somewhat weaker effects were observed when NaCl was replaced with sucrose. In some preparations, 2.2 .times. 10-4 M diltiazem reduced the contractile force without significant influence on the electrical activity in Na+-free Locke solution. CoCl2 (3 mM) inhibited the evoked activities in normal and Na+-free solutions. Possible mechanisms for the relaxing effects of diltiazem on isolated guinea pig tenia coli were discussed.