HALIDE TRANSPORT IN XENOPUS OOCYTES

1. Radioisotopes and intracellular microelectrodes were used to characterize the permeability of Xenopus oocytes to chloride and other halides. 2. Uptake of Cl-36 had a half-time for equilibration of approximation 3 h, with an initial rate of Cl- entry corresponding to a permeability coefficient of 3.9 x 10(-7) cm/s, and an equilibrium uptake of Cl-36 of 33 mM. 3. Replacement of bathing Na+ by K+ depolarized the oocytes from - 46 to -7 mV and stimulated influx approximately 3-fold. 4. Influx was linearly dependent on bathing [Cl-] and was temperature dependent with an activation energy of 46 kJ/mol. Influx of I-125 or Cl-36 was not affected by the presence of equal concentrations of other halides or thiocyanate. These results are consistent with a channel-mediated entry mechanism. 5. Diphenylamine-2-carboxylate (DPAC) and 9-anthracene carboxylate (9-AC), blockers of Cl- channels in other cells, inhibited Cl- entry with dissociation constants (K(d)s) of approximately 5 x 10(-4) and approximately 10(-3) M, respectively. Inhibitors of Cl- -HCO3- exchange or Na+-K+-2Cl- co-transport did not affect Cl- influx. 6. Attempts to lower or raise intracellular Ca2+ with BAPTA or A23187, respectively, were also without effect on Cl- influx. 7. The halide selectivity sequence determined with isotopes was I- (3.2) > Br-(1.3) > Cl- (1.0). However, DPAC inhibited almost all of the Cl-36 influx but only a small fraction of I-126 influx. 8. Replacement of bathing Cl- by I- or Br- resulted in hyperpolarizations, from which the same selectivity sequence was determined. 9. Replacement of bathing Cl- by gluconate caused a marked depolarization, which was inhibited by DPAC and, less potently, by 9-AC.