Specificity of H ion concentration as a carotid chemoreceptor stimulus.

The present study was designed to separate quantitatively the relative contributions of (H+) and Pco2 as chemoreceptor stimuli. The integrated electrical activity from the entire Hering's nerve of the cat was measured and correlated with values of (H+), Pco2, and Po2 of arterial blood. By utilizing a combination of respiratory and metabolic acidosis or alkalosis, the effect of (H+) on carotid body nerve activity could be separated from that of Pco2. Most studies were performed at high Po2, a few against a changing hypoxic background. The results indicate: 1) the pre-eminence of (H+) as a chemoreceptor stimulus, CO2 acting only by virtue of its effect in altering (H+); 2) the relationship between (H+) or Pco2 and chemoreceptor activity is nonlinear; 3) the potentiation between hypoxia and hypercapnia at the chemoreceptor level is due primarily to interaction between low oxygen tension and increased (H+), independent of Pco2. The significance of these findings to the exchange of CO2 and of (H+) and (HCO3-) ions between the intracellular and extracellular milieu of the carotid chemoreceptor cells is discussed.