Effect of procaine on membrane potential and intracellular pH in Xenopus laevis oocytes

The effect of the local anaesthetic procaine on the intracellular pH, pHi, and electrophysiological properties of full-grown Xenopus oocytes was studi ed. In spite of its interference with both the pH-sensitive microelectrodes and fluorescent probe BCECF, we have shown that procaine induced an intrac ellular acidification rather than the alkalization commonly observed in mos t cells. The resting pHi of Xenopus oocytes loaded with BCECF was 7.36 +/- 0.04 (n = 16). Addition of 10 mM procaine to the bath at pH 7.5 caused pHi to decrease to a new steady state value of 6.97 +/- 0.05 (n = 9). A similar behaviour of pHi was observed with microelectrodes. Procaine also promoted a rise in membrane conductance and a membrane depolarization. These change s in membrane potential and conductance were not caused by the decrease in pHi since the addition of sodium propionate at pH 7.5 produced the same dec rease of pHi as procaine, but resulted in only a slight depolarization with superimposed oscillations. Current measurements using two-electrode voltag e cramp showed that the depolarization was associated with an inward curren t. No significant effect on this current was observed when replacing CI, K or Na in the external medium. The absence of effect of CI and K channel inh ibitors argues against the involvement of CI and K currents during the proc aine response.