TAURINE PERMEATION THROUGH SWELLING-ACTIVATED ANION CONDUCTANCE IN RAT IMCD CELLS IN PRIMARY CULTURE

Whole cell recordings were performed on rat inner medullary collecting duct IMCD) cells in primary culture. With 140 mmol/l CsCl in bath and pipette we find within 10 min a 60-fold increase in membrane conducta nce from 0.02 +/- 0.003 to 1.2 +/- 0.1 nS/pF when bath osmolarity is d ecreased from 600 to 500 mosmol/l. The effect is due to the activation of an outwardly rectifying anion conductance with the anion selectivi ty SCN- > I- > NO3- > Br- > Cl- > F- > isethionate > gluconate greater than or equal to aspartate greater than or equal to glutamate. A rela tive permeability of the organic osmolyte taurine to Cl- (P-taurine: P -Cl-) of 0.15 was detected. With taurine in pipette and bath, the chan nel exhibits a nearly identical activation and sensitivity profile to a variety of anion channel blockers as under symmetrical Cl- condition s. Furthermore, the 50% inhibitory concentration value for the effect of 5-nitro-2-(3-phenylpropyl-amino)benzoate on both currents is virtua lly identical. We conclude that hypotonic stress increases the anion c onductance of rat IMCD cells and that this anion conductance mediates taurine efflux.