Contribution of a net transmembrane HCO3- flux to intracellular acid-base regulation.

Experiments were performed to determine the relative effects of a net extracellular-to-intracellular HCO3- flux and of elevated carbon dioxide tension (PCO2) on cellular acid-base regulation. Isolated rabbit hearts were perfused by recirculating a small volume of Ringer solution in which the PCO2 and the HCO3- concentration could be independently altered. Net HCO3- flux was assessed by the disappearance of HCO3- from perfusate. Between 40 and 100 Torr PCO2, a HCO3- flux into the cell occurs only when perfusate HCO3- concentration is increased. Therefore, by selective manipulation of perfusate HCO3- and PCO2 it is possible to induce hypercapnia with or without an accompanying HCO3- flux. When perfusate HCO3- concentration was increased from 20 to 36 mM, cellular HCO3- concentration increased from 22.5 +/- 0.8 to 26.1 +/- 1.0 mM at 40 Torr PCO2 and from 27.8 +/- 0.7 to 34.1 +/- 1.4 mM at 98 Torr PCO2. These increases can be accounted for by the amount of HCO3- that disappeared from the perfusate. The results suggest that most of the initial cell CO2 buffering is provided by the net HCO3- flux in addition to the passive physicochemical buffering.