Conduction in the mammalian auricle as affected by changes in hydrogen ion concentration.

Abstract

The writers have performed a series of experiments upon the hearts of dogs perfused with oxygenated Locke's solution by a modified Langendorff method. Observations were made upon the effect of changes in (1) hydrogen ion concentration and (2) oxygen content of the perfusing fluid upon the transmission of the excitatory process in the auricle. Electrical records were obtained by placing paired non-polarizable electrodes upon the auricle in such a way that the conduction interval was recorded over a single stretch of 12-16 mm. or over consecutive portions of 6-8 mm each. Each pair of electrodes was connected with a galvanometer string.

The effects of changes in pH of the perfusate upon conduction in the auricle were consistent with those reported by Andrus and Carter 1 on the A-V conduction. An increase in the alkalinity of the perfusing fluid, pH 7.8, was attended by a faster rate of transmission both in the naturally beating and rhythmically driven heart. In the latter the same result was obtained whether the stimulating electrodes were placed upon the base of the auricle or upon the appendix. A pH lower than normal, pH 7.0, caused the excitatory process to be propagated more slowly, and again, this result was obtained in the auricles following the sinus rhythm or rhythmic induction shocks introduced through electrodes placed either upon the base or tip of the auricle. In the naturally beating heart an increase in rate followed change to a higher pH and a fall in rate a lower one. Both the development and propagation of the excitatory process were, then, affected by changes in reaction of the fluid bathing the tissue and in the same direction.

In certain experiments the perfusing solutions were saturated with nitrogen in place of oxygen with striking results. If the auricle was perfused with an oxygen-free solution of pH 7.0 there resulted almost immediately a profound reduction in the transmission rate. Soon there appeared a condition in which the transmission of the excitation became progressively slower the farther the wave traveled from its point of origin, so that records taken with three pairs of electrodes showed a longer transmission interval between the second and third than between the first and second. As this condition progressed the muscle under the distal contacts responded to only every second wave of excitation as recorded at the middle electrodes and finally ceased altogether to become excited.