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+(Rb-86(+)) 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 increase (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 Ca2+-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.