A Ca²⁺-dependent K⁺-channel in freshly isolated and cultured chick osteoclasts

Calcium-activated potassium channels were found in embryonic chick osteoclasts using the patch-clamp technique. The activity of the channel was increased by both membrane depolarisation and an increase in intracellular Ca²⁺ concentration in the range 10^-5 to 10^-3 M. In the cell-attached-patch configuration the channel was only active at extreme depolarising potentials. Ca²⁺ addition to the cytoplasm via ionomycin increased channel activity at the resting membrane potential of the osteoclast. The channel had a single-channel conductance of 150 pS in the inside-out patch under symmetrical K⁺ conditions (150 mM) and was selective for potassium ions. During sustained application of increased [Ca²⁺] at the cytoplasmic side of inside-out patches, channel activity sometimes decreased again after the initial increase (desensitization). The results established the properties of the single channels underlying an outward rectifying K⁺ conductance in chick osteoclasts described previously by us.