Fig. 5. Block of Cx32 hemichannel currents by acidosis. Samples of whole-membrane currents in isolated oocytes expressing human Cx32 (I) induced by repetitive pulses (V; +80 mV, 5 s) applied at the holding potential of - 40 mV. At neutral pH, depolarization induced slowly activating outward currents that on returning to - 40, became inward and close over a slow time course. Large currents with these unusual characteristics were recorded exclusively in oocytes injected with Cx32 RNA and never observed in oocytes injected only with the anti-Cx38 oligonucleotide (1). The voltage-activated component (arrows) and tail currents (arrowheads) were almost completely eliminated by extracellular acidification (pH 6.2 with 100% CO2), a treatment known to block hemi- and gap-junction channels. It should be noted that acidification also decreased the background current at the holding potential of -40 mV (asterisk), suggesting the presence of certain background activation. In fact, at resting conditions, where the membrane potential is free, the resting membrane potential depolarized progressively in conjunction with a substantial increase in the membrane conductance as time elapsed after Cx32 RNA injection. After 24-48 h, the membrane potential was -32 ± 4 vs. - 49 ± 5 mV of control oocytes (mean ? SD; paired t test, P < 0.01), and the input resistance decreased from 0.8 ± 0.3 to 0.4 ± 0.2 MΩ (P<0.01).
J. Neurosci. 19, 3752.