Chronotropic response of isolated guinea pig atria to alterations in pCO2, bicarbonate, and pH

The effect of respiratory and metabolic alterations of extracellular pH on the rate of spontaneous contractions of isolated atria of guinea pig hearts was examined using a CO2HCO3 buffer system. The rate of contractions increased with the increase in pH in the range of 6.8 to 8.25. Respiratory and metabolic alterations of pH produced quantitatively similar chronotropic responses. However, time-course of rhythm change was significantly faster during respiratory alterations of pH. When perfusate pCO2 and bicarbonate were simultaneously raised at constant pH, the rate of contractions initially fell and then returned to the control value. On the return to control solution a rapid rise in the rate of contractions was followed by a slow return to the control value. We conclude that the chronotropic responses to acid-base alterations are mediated by changes in the intracellular pH.