title: Regulation of endogenous chloride conductance in Xenopus oocytes.
abstract: Radiotracer (86Rb, 125I) efflux measurements and intracellular microelectrode recording were performed to study the cellular mechanisms that regulate the endogenous ionic conductances in Xenopus oocytes. Addition of isoproterenol (Iso, 10(-5) M) caused a marked increase in 86Rb efflux, with a time course that is in good agreement to Iso-elicited membrane hyperpolarization. Thus, radiotracer efflux measurement appears to be a sensitive assay method to study stimulus-secretion coupling in oocytes. 125I efflux was suppressed by the C1- channel blocker diphenylamine-2-carboxylate, but was insensitive to bumetanide. Elevation of ambient [Ca2+] from 0.4 to 10 mM resulted in an eminent increase in 125I efflux for up to approximately 20 min. Acetylcholine (10(-5) M), which mobilizes cell Ca2+, also enhanced 125I efflux. Iso although increased intracellular cAMP level approximately 2-fold, but showed no stimulatory effect on 125I efflux. Addition of 8-(-4-chlorophenylthio)-cAMP (1 mM), or of forskolin (10(-5) M) plus the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (2 x 10(-4) M), also failed to enhance 125I efflux. These results suggest that, in sharp contrast to the mechanisms for Cl-conductance regulation in mammalian Cl-secreting epithelia, the endogenous Cl- conductance in Xenopus oocytes is, under normal physiological conditions, primarily regulated by intracellular Ca(2+)- rather than a cAMP-mediated signaling mechanism.
authors.affiliation: Department of Physiology, University of California, San Francisco 94143-0130.
authors.forename: A C
authors.initials: AC
authors.lastname: Chao
authors.forename: Y
authors.initials: Y
authors.lastname: Katayama
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D018118:Chloride Channels; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005260:Female; D007454:Iodides / Q000378:metabolism; D007457:Iodine Radioisotopes; D007473:Ion Channels / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000187:drug effects / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012413:Rubidium / Q000378:metabolism; D012414:Rubidium Radioisotopes; D013873:Thionucleotides / Q000494:pharmacology; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D018118:Chloride Channels; D007454:Iodides; D007457:Iodine Radioisotopes; D007473:Ion Channels; D008565:Membrane Proteins; D012414:Rubidium Radioisotopes; D013873:Thionucleotides; D062367:ortho-Aminobenzoates; D002034:Bumetanide; D005576:Colforsin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; C001209:fenamic acid; D000242:Cyclic AMP; D007545:Isoproterenol; D012413:Rubidium; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine