Biochem Biophys Res Commun 1991 Nov 14;1803:1377-82.

Regulation of endogenous chloride conductance in Xenopus oocytes.

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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.

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Genes referenced: camp