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 36Cl had a half-time for equilibration of approximately 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 36Cl 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 125I of 36Cl 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 (Kds) 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) greater than Br- (1.3) greater than Cl- (1.0). However, DPAC inhibited almost all of the 36Cl influx but only a small fraction of 125I 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.
Katayama
Y
Y
Cardiovascular Research Institute, NIH Cystic Fibrosis Research Center, San Francisco, CA.
Widdicombe
J H
JH
D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D001692:Biological Transport; D001965:Bromides / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D006219:Halogens / Q000378:metabolism*; D007454:Iodides / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013997:Time Factors; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D000873:Anthracenes; D001965:Bromides; D002712:Chlorides; D006219:Halogens; D007454:Iodides; D062367:ortho-Aminobenzoates; C010030:9-anthroic acid; C001209:fenamic acid; D012964:Sodium; D011188:Potassium; D002118:Calcium