Effects of electrolyte composition and temperature of extra-cellular fluid on coronary artery contraction

We studied the effects of the electrolyte composition (K, Ca, Na, Mg) and the temperature of the extracellular fluid on the tension development of isolated canine coronary arterial strips. In 20 mEq/l K solution, the calcium produced a dose-dependent contraction at concentrations higher than 0.2 mEq/l. This Ca-induced contraction was strongly inhibited by hypothermia below 20 degrees C and also by 30 mEq/l magnesium. In the presence of 20 mEq/l K, the reduction of sodium concentrations to less than 90 mEq/l increased the tension which was inversely related to the concentration. Cooling below 25 degrees C of this solution or addition of 20 mEq/l magnesium to low-Na solution markedly reduced contractions. It is concluded that the electrolyte containing K20, Ca0.1, Na110 and Mg30mEq/l or cooling below 20 degrees C can maintain relaxation in the dog coronary artery.