ELECTROPHYSIOLOGY OF A CLONAL OSTEOBLAST-LIKE CELL-LINE - EVIDENCE FOR THE EXISTENCE OF A CA-2+-ACTIVATED K+ CONDUCTANCE

Intracellular microelectrode measurements were made on a well-characterized osteoblast-like clonal cell line isolated from a rat osteosarcoma. In serum-free medium, stable membrane potentials of -42 .+-. 9 mV (SD, n = 190) were recorded. Ion substitution experiments suggested that this membrane potential is primarily a Na+/K+ diffusion potential. Input resistance was correlated strongly with colony size, ranging from 49 .+-. 18 M.omega. (SD, n = 14) for colonies of 1-3 cells, to 4 .+-. 4 Mo (SD, n = 164) for colonies of 100 or more cells. These results are consistent with the existence of low resistance intercellular junctions. Application of the carboxylic C ionophore A23187 by pressure microejection onto the cell surface resulted in a transient hyperpolarization and concomitant decrease in input resistance. Both these effects are consistent with an increased K+ conductance. Ion substitution experiments demonstrated that the degree of hyperpolarization was dependent on the external concentration of both K+ and Ca+. Quinine, a blocker of Ca2+-activated K+ channels, inhibited the ionophore-induced hyperpolarization in a dose-dependent manner. These cells exhibit a Ca2+-activated K+ conductance.