Abstract

In contrast to procaine, Xylocaine does not inhibit the extra oxygen consumption induced by caffeine or potassium depolarization. Xylocaine increases the extra oxygen consumption which can occur without any mechanical changes. If the muscle is made mechanically refractory by high concentrations of potassium, Xylocaine has no effect on respiration. The effect of Xylocaine depends upon extracellular pH, which determines the ratio of charged to uncharged forms; at pH 6.0, when the predominant form of Xylocaine is charged, the stimulatory effect on respiration is abolished. The influence of Xylocaine on the oxygen consumption is thought to be related to the level of free Ca in the cell; the effect does not disappear when Ca is omitted from the Ringer's solution.