Effect of PH on the Sino-atrial Node Cells and Atrial Muscle of Dog

Effects of pH (6.0, 6.5, 7.0, 7.4, 8.0, 8.5 and 9.0) on the canine sino-atrial node were studied using isolated right atrial preparations which were obtained from puppies and perfused with oxygenated Tyrode solution through the dorsal right atrial artery (sinus node artery). First, the preparations were perfused by normal solution (pH 7.4), and then by one with a different pH. Low pH perfusate prolonged the cycle length and depressed the atrial contraction. These effects occurred slowly and it took 5-7 min to reach the maximum change. Alkaline solutions caused opposite changes. In both low and high pH solutions, the changes in cycle length were not stronger than those for atrial contraction. The depression in low pH solution or the enhancement in high pH solution became more prominent with the decrease or increase in the pH. As for the configuration of action potential of the sino-atrial node cells, acid solutions caused reduction in the amplitude of action potential and the rate of phase 4 depolarization, and prolonged the duration of action potential. On the other hand, alkaline solutions increased the rate of phase 4 depolarization and amplitude of action potential, and shortened the duration of action potential. We also examined the influence of pH on the effect of norepinephrine on the sino-atrial node. The positive chronotropic and inotropic responses to norepinephrine were maximal in pH 7.4 solution.