PCO2 of the proximal tubular fluid and the efferent arteriolar blood in the rat kidney.

Recordings in vivo of the carbon dioxide tension of the proximal tubular fluid and of the efferent arteriolar blood were performed with PCO2 microelectrodes in the rat kidney. The buffer lines of the efferent arteriolar blood and systemic arterial blood were determined with an ultramicro equilibration system and the acid-base status of the systemic arterial blood was measured. The intratubular PCO2 was significantly higher than the PCO2 of the arterial blood, and the PCO2 of the efferent arteriolar blood was significantly lower than that of the arterial blood. The buffer capacity was higher and the bicarbonate concentration slightly lower for the efferent arteriolar blood than for the arterial blood. It is concluded that a PCO2 difference exists across the tubular wall and that the high intratubular PCO2 favours a chemical equilibrium of the carbonic acid-bicarbonate system in the proximal tubular fluid. It is supposed that the slightly lowered bicarbonate concentration in the efferent arteriolar blood is an effect of the glomerular ultrafiltration process.