Cell-attached recordings of the volume-sensitive anion channel in rat pancreatic beta-cells.

The cell-attached configuration of the patch-clamp technique was used to study the volume-sensitive anion conductance in isolated rat pancreatic beta-cells at the single-channel level. In unstimulated cells, current level was close to zero. Exposure of cells to a 33% hypotonic solution resulted in the generation of an inward current at 0 mV pipette potential. A similar inward current was elicited by a rise in glucose concentration or by addition of alpha-ketoisocaproate. In contrast, the sulphonylurea tolbutamide was ineffective. The inward current evoked by hypotonic solutions consisted of occasional discreet channel events interspersed with periods of current noise which could not be clearly resolved into unitary channel events. Stimulation with glucose resulted in a predominantly noisy pattern of current. With a reduced [Cl(-)] pipette solution, regular channel openings could be resolved in the presence of a stimulatory glucose concentration, with a calculated conductance of 215 pS. Channel activity could also be recorded in excised inside-out patches, though rapid 'rundown' occurred under such conditions. It is concluded that hypotonic solutions and glucose activate the volume-sensitive anion channel in the cell-attached configuration by increasing channel open probability. This generates an inward current in non-voltage-clamped cells. The channel showed complex kinetics which depended in part upon extracellular [Cl(-)].