Volume-activated DIDS-sensitive whole-cell chloride currents in trout red blood cells

1. The nystatin-perforated whole-cell recording mode of the patch-clamp technique was used to investigate the membrane conductance of trout (Oncorhynchus mykiss) red blood cells in the steady state, 5 min after exposure to hyposmotic medium and 10 min after return to normal isosmotic medium. 2. Whole-cell I-V relations showed outward rectification when red blood cells were bathed in isosmotic (320 mosmol l-1) saline solution and the patch pipette was filled with 117 mM KCl. The membrane conductance was 2.58 +/- 0.59 nS (number of experiments, n = 18) between 0 and 100 mV and 1.32 +/- 0.19 nS (n = 18) between 0 and -100 mV. Removal of Cl- from the extracellular side or incubation with the Cl- channel blocker DIDS caused a reduction in whole-cell membrane conductance by more than 50%, indicating that the membrane current was generated by Cl- ions. The remaining conductance was voltage independent and probably due to non-selective cation conductance. 3. The membrane conductance increased approximately 2-fold after cell swelling induced by exposure to hyposmotic saline solution (215 mosmol l-1). This effect was abolished in Cl(-)-free hyposmotic medium or in the presence of DIDS. 4. The return to isosmotic solution produced a fall in membrane conductance to, or below, control values. 5. We conclude that trout red blood cells possess a significant Cl- conductance in the steady state which is reversibly activated during cell swelling and contributes to volume recovery.