A new microelectrode method for simultaneous measurement of pH and PCO2.

A liquid-membrane pH-PCO2 microelectrode is described for the simultaneous measurement of pH and PCO2 in tissues and body fluids. The microelectrode is simple and easy to fabricate. It can be used to measure HCO3 concentration in solutions at chemical equilibrium. In the physiological range the microelectrode response is linear with nearly Nernstian slopes for PCO2 (61.2 +/- 2.0 mV/log10 PCO2) and pH (63.7 +/- 1.9 mV/pH units) (n = 14) at 37 degrees C. The PCO2 response is independent of the solutions' pH, anionic composition, and presence of serum proteins. In randomly micropunctured rat surface proximal tubules, pH averaged 6.80 +/- 0.04 and PCO2 averaged 57.7 +/- 4.6 mmHg (n = 22), whereas in the adjacent peritubular capillaries pH was higher (7.27 +/- 0.03) but PCO2 was not different (55.7 +/- 4.6 mmHg) (n = 22). Systemic arterial PCO2 was significantly lower compared with the renal cortex and averaged 37.4 +/- 2.4 mmHg (n = 14). Directly measured and pH-PCO2 microelectrode-derived HCO3 concentrations in systemic arterial blood, surface fluid bathing the kidney, and randomly micropunctured proximal tubules were approximately equal.