A new design of double-barrelled microelectrodes for intracellular pH-measurement in vivo.

Intracellular pH (pHi) is one important regulator of cellular function. Most determinations of pHi in vivo have been performed by using indirect methods, e.g. CO2/HCO3 or DMO techniques, since no suitable direct method for reliable in vivo measurements have been available. In the present study a new type of double-barrelled microelectrode for simultaneous in vivo measurements of pHi and membrane potential (Em) is presented. The electrode was constructed on the basis of a combined recessed- and pencil-tip design. The tip diameter of the double-barrelled microelectrode was about 1.5 microns. The response of the pH channel was 55-60 mV/pH unit and the response time was between 30 s and 1 min. In vivo measurements of pHi and Em of rabbit skeletal muscle fibers are presented. A mean pHi of 7.00 (in 8 animals) at a membrane potential of -90.3 mV (arterial pH: 7.30, arterial PCO2: 6.39 kPa) was obtained. The new design of pH microelectrode offers some advantages over previously described microelectrodes and is well suited for in vivo measurements.