Pathways for K+ transport across the bovine articular chondrocyte membrane and their sensitivity to cell volume

The contributions of various K+ transport pathways in bovine chondrocytes isolated from articular cartilage and their responses to changes in cell volume have been studied. K+(86Rb+) uptake mediated by the Na(+)-K(+) pump and Na(+)-K(+)-2Cl- cotransporter were stimulated by cell shrinkage, the latter as part of the regulatory volume increases (RVI) response, the former as an indirect effect resulting from the rise in intracellular Na+ concentration during RVI. For both transporters, there was an increase in the maximum velocity with no detectable effect on the Michaelis constant. There was no evidence for volume-sensitive K+ transport mediated by the K(+)-Cl- cotransporter, or Ca(2+)-activated K+ channels. However, chondrocyte swelling stimulated a ouabain- and bumetanide-insensitive K+ flux sensitive to pimozide and other drugs, which exhibited some of the properties of the relatively nonspecific volume-sensitive "osmolyte" channel described in other cell types.