A Ca(2+)-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 increases (desensitization). The results established the properties of the single channels underlying an outward rectifying K+ conductance in chick osteoclasts described previously by us.