The Ca(2+)-induced leak current in Xenopus oocytes is indeed mediated through a Cl- channel.
Defolliculated oocytes of Xenopus laevis responded to removal of external divalent cations with large depolarizations and, when voltage clamped, with huge currents. Single channel analysis revealed a Cl- channel with a slope conductance of about 90 pS at positive membrane potentials with at least four substates. Single channel amplitudes and mean channel currents had a reversal potential of approximately -15 mV as predicted by the Nernst equation for a channel perfectly selective for Cl-. Readdition of Ca2+ immediately inactivated the channel and restored the former membrane potential or clamp current. The inward currents were mediated by a Ca2+ inactivated Cl- channel (CaIC). The inhibitory potency of Ca2+ was a function of the external Ca2+ concentration with a half maximal blocker concentration of about 20 microM. These channels were inhibited by the Cl- channel blockers flufenamic acid, niflumic acid and diphenylamine-2-carboxylate (DPC). In contrast, 4,4'-acetamido-4'-isothiocyanatostilbene-2, 2'-disulfonicacid (SITS), another Cl- channel blocker, led to activation of this Cl- channel. Like other Cl- channels, the CaIC was activated by cytosolic cAMP. Extracellular ATP inhibited the channel while ADP was without any effect. Injection of phorbol 12-myristate 13-acetate (PMA), a protein kinase C activating phorbol ester, stimulated the Cl- current. Cytochalasin D, an actin filament disrupting compound, reversibly decreased the clamp current demonstrating an influence of the cytoskeleton. The results indicate that removal of divalent cations activates Cl- channels in Xenopus oocytes which share several features with Cl- channels of the CLC family. The former so-called leak current of oocytes under divalent cation-free conditions is nothing else than an activation of Cl- channels.
Weber
W M
WM
Institut für Tierphysiologie, Jusois-Liebig-Universităt, Giessen, FRG.
Liebold
K M
KM
Reifarth
F W
FW
Clauss
W
W
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D018118:Chloride Channels / Q000187:drug effects* / Q000502:physiology; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology; D005439:Flufenamic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects* / Q000502:physiology; D009866:Oogenesis; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology
D018118:Chloride Channels; D010566:Virulence Factors, Bordetella; D062367:ortho-Aminobenzoates; D015638:Cytochalasin D; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D005439:Flufenamic Acid; D000255:Adenosine Triphosphate; D002772:Cholera Toxin; C001209:fenamic acid; D000242:Cyclic AMP; D037342:Pertussis Toxin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine