Hypoxic suppression of K+ currents in type I carotid body cells: selective effect on the Ca2(+)-activated K+ current.

Whole-cell K+ currents were recorded in isolated type I carotid body cells using the patch-clamp technique. Hypoxia (pO2 25 torr) reversibly suppressed K+ currents in a voltage-dependent manner: maximal effects were seen at low, positive test potentials, where the Ca2(+)-activated component of K+ currents was greatest. Enhancing this component with 5 microM BAY K 8644 exaggerated the effects of hypoxia, and when the component was inhibited (100 microM Cd2+ or 5 microM nifedipine) hypoxic effects were abolished. As hypoxia does not affect Ca2+ currents directly, these data indicate the suppressive effect of hypoxia is selective for the Ca2(+)-activated component of K+ currents in type I cells.