Uptake of bromosulfophthalein via SO42-/OH- exchange increases the K+ conductance of rat hepatocytes

In confluent primary cultures of rat hepatocytes, micromolar concentrations of bromosulfophthalein (BSP) lead to a sizeable hyperpolarization of membr ane voltage. The effect is a saturable function of BSP concentration yieldi ng an apparent value of 226 mu mol/l and a V-max of -10.3 mV. The BSP-induc ed membrane hyperpolarization is inhibited by the K+ channel blocker Ba2+, and in cable-analysis and ion-substitution experiments it becomes evident t hat the effect is due to a significant increase in cell membrane K+ conduct ance. Voltage changes were attenuated by the simultaneous administration of SO42-, succinate, and cholate (cis-inhibition) and increased after preincu bation with SO42- and succinate (trans-stimulation), suggesting that the ef fect occurs via BSP uptake through the known SO42-/OH- exchanger. Microfluo rometric measurements reveal that BSP-induced activation of K+ conductance is not mediated by changes in cell pH, cell Ca2+, or cell volume. It is con cluded that K+ channel activation by BSP (as well as by DIDS and indocyanin e green) may reflect a physiological mechanism linking the sinusoidal uptak e of certain anions to their electrogenic canalicular secretion.