EFFECTS OF ANION SUBSTITUTIONS ON POTASSIUM-INDUCED PHASIC AND TONIC CONTRACTION IN TAENIA COLI

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It was reported that high-potassium caused a rapid rise of tension which gradually declined to a new steady state level in strips of guinea pig taenia coli, and that the K-induced contracture was composed of phasic and tonic responses (1, 2). When the sucrose gap technique was used, a brief burst of spike discharges was recorded to correspond to the phasic response of K-induced contracture in taenia coli and membrane depolarization was correlated to the tonic response (3). It was proposed that in the phasic contraction, tissue calcium was released to initiate contraction, whereas in the tonic contraction, external calcium crossed the membrane to initiate it and that the transmembrane calcium transport involved in the tonic response was dependent on metabolism (1, 2). In the tonic response the Ca transport process was possibly coupled to an active Na efflux (2, 4). On the other hand, contracture studies on single fiber of frog skeletal muscle showed that the anion substitutions with NO<SUB>3</SUB> and SCN lowered the threshold concentration of potassium required for contracture and increased the contracture tension only at potassium concentrations below the level required for maximum tension development (5). Another contracture potentiating anion, Br, had similar effects on K-induced contracture in the frog toe muscle (6). The present experiments were undertaken to investigate the possibility of these anions, having a potentiating effect on skeletal muscle, differently modifing the phasic response and the tonic one, in contracture of taenia coli with high-potassium.
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EFFECTS OF ANION SUBSTITUTIONS ON POTASSIUM-INDUCED PHASIC AND TONIC CONTRACTION IN TAENIA COLI

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