Stretch-activated channels in the basolateral membrane of single proximal cells of frog kidney

Epithelial cells are capable of regulating their volume in response to osmotic swelling or shrinkage. In the present paper a channel is described which may be involved in such a volume-regulatory response. Channels were studied in cell-attached patches of the basolateral membrane of cells isolated from frog kidneys using the patch-clamp technique. The open probability of the channels is increased by the application of negative pressure to the rear of the patch pipette or by bathing the cells in hypotonic fluid. In addition, the channels are voltage-sensitive, such that depolarisation increases the open probability. The channels have a conductance of 25 pS with amphibian Ringer as the pipette solution and appear not to discriminate between potassium and sodium. Replacement of chloride by gluconate as the dominant anion in the pipette solution did not affect the current/voltage relationship, suggesting that the channels are cation-non-selective. Inward currents are observed at the resting membrane potential with either potassium or sodium as the dominant cation in the pipette solution: this obviates the channels serving a role as the route for solute exit from the cell during a volume-regulatory decrease response and suggests that they may act as the transduction mechanism sensing changes in cell volume.