The effects of calcium and temperature on the tension of isolated canine coronary arterial strips were studied. In 20 mEq. l(-1) K solution, the tension was significantly increased from 0 mg with 0 mEq. l(-1) Ca to 33 +/- 18 mg with 0.2 mEq. l(-1) Ca at 37 degrees C, from -40 +/- 18 mg with 0 mEq. l(-1) Ca to -17 +/- 11 mg with 0.2 mEq. l(-1) Ca at 30 degrees C, from -77 +/- 19 mg with 0 mEq. l(-1) Ca to -52 +/- 17 mEq. l(-1) with 1 mEq. l(-1) Ca at 25 degrees C, from -88 +/- 13 mg with 0 mEq. l(-1) Ca to -41 +/- 18 mg with 2 mEq. l(-1) Ca at 20 degrees C, from -125 +/- 16 mg with 0 mEq. l(-1) Ca to -116 +/- 13 mg with 2 mEq. l(-1) Ca at 15 degrees C. Ca higher than 0.2 mEq. l(-1) produced a dose-dependent increase in tension between 37 degrees C and 15 degrees C. In spite of the presence of 4 mEq. l(-1) Ca, the development of tension was strongly supressed by lowering the temperature below 20 degrees C, and completely inhibited at 10 degrees C. The rate of a decrease in tension caused by cooling was about 5.5 mg. degrees C(-1). This study demonstrated that Ca(2+) produced a dose-dependent increase in tension in high-K solution, which was suppressed as the temperature was lowered.

The effects of sodium and temperature on tension of isolated canine coronary arterial strips were studied. In 20 mEq. l(-1) K solution, the strength of tension was inversely related to the Na concentration. At 37 degrees C, the tension was significantly increased at 70 mEq. l(-1) Na and below. The tension was gradually suppressed by lowering of the temperature from 37 degrees C to 10 degrees C. At 10 degrees C, tension did not developed significantly at Na concentrations between 127 mEq. l(-1) and 12 mEq. l(-1). It was concluded that the decrease in Na concentrations increased the tension of the canine coronary artery and the lowering of temperature supressed the tension inducted by the decrease in Na concentrations.