Identification of Ca²⁺‐activated K⁺ channels in cells of embryonic chick osteoblast cultures

Primary cultures of embryonic chick osteoblasts consist of a heterogeneous cell population. Patch clamp measurements were done on 1‐ to 5‐day‐old osteoblasts, osteocytes, fibroblastlike cells, and cells that could not be classified on morphologic criteria. The measurements showed the omnipresence of depolarization‐activated high‐conductance channels in cell‐attached patches. The whole‐cell experiments showed an outward rectifying conductance activating at positive membrane potentials. Channels underlying the latter conductance were found to be K⁺ conducting in outside‐out membrane patches. The activation potential of the outward rectifying K⁺ conductance shifted to negative membrane potentials upon increasing the intracellular Ca²⁺ concentration within the range of 10⁻⁸–10^−3.2 M. The same happened with the activation potential of the K⁺ channels found in outside‐out patches. Finally, inside‐out patch experiments directly demonstrated the dependency of the activation potential of K⁺ channels on Ca²⁺ ions. Thus the identity and main characteristics of Ca²⁺‐activated K⁺ channels expressed by the various cell types present in chick osteoblast cultures have now been established. Decreased input resistances were found in cells of cultures more than 2 days old. This is consistent with the establishment of electrical coupling between the cells. Functions in which Ca²⁺‐activated K⁺ channels could play a role are discussed.