Voltage-activated K+ conductances in freshly isolated embryonic chicken osteoclasts

Patch-clamp measurements on freshly isolated embryonic chicken osteoclasts revealed three distinct types of voltage-dependent K+ conductance. The first type of conductance, present in 72% of the cells, activated at membrane potentials less negative than -30 to -20 mV and reached full activation at +40 mV. It activated with a delay, reached a peak value, and then inactivated with a time constant of approximately 1.5 s. Inactivation was complete or almost so. Recovery from inactivation, at -70 mV, had a time constant of roughly 1 s. The conductance could be blocked, at least partly, by 4 mM 4-aminopyridine. The second type of conductance (present in all cells) activated at membrane potentials more negative than -40 to -80 mV and reached full activation at -130 mV. Activation potential and maximal conductance were dependent on the extracellular K+ concentration. Inactivation of the conductance first became apparent at membrane potentials more negative than -100 mV and was a two-exponential process. The conductance could be blocked by external 5 mM Cs+ ions. The third type of conductance (present in all cells) activated at membrane potentials more positive than +30 mV. Generally, the conductance did not inactivate.