Influence of extracellular Ca2+ on endogenous Cl- channels in Xenopus oocytes.
Removal of Ca2+ from the external bath solution evoked marked depolarization and large currents (up to several microamperes) in voltage-clamped defolliculated oocytes of Xenopus laevis. The resulting current was not carried by a cation influx but was due to a huge Cl- efflux, which could be strongly inhibited by the Cl- channel blockers flufenamic acid and niflumic acid. Removal of Mg2+ or Ba2+ from the solutions had the same effects as removing Ca2+. The reversal potential of -12 mV also indicated that Cl- channels were responsible for the large currents. Patch-clamp studies revealed a single-channel slope conductance of 90 pS. During oocyte maturation these channels remained active. The half-maximal Ca2+ concentration of about 20 microM showed that quite low doses of extracellular Ca2+ profoundly influence the electrical properties of the oocyte membrane.
Weber
W M
WM
Institut für Tierphysiologie, Justus-Liebig-Universität, Giessen, Germany.
Liebold
K M
KM
Reifarth
F W
FW
Uhr
U
U
Clauss
W
W
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D005439:Flufenamic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials; D009544:Niflumic Acid / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D014982:Xenopus laevis
D018118:Chloride Channels; D001464:Barium; D009544:Niflumic Acid; D004533:Egtazic Acid; D005439:Flufenamic Acid; D008274:Magnesium; D011188:Potassium; D002118:Calcium