title: Calcium dependence and distribution of calcium-activated chloride channels in Xenopus oocytes.
abstract: 1. The Ca(2+)-dependent Cl- current (ICl,Ca), expressed in the plasma membrane of Xenopus oocytes, was examined in excised inside-out macropatches using a rapid perfusion system. 2. Application of Ca(2+)-containing Ringer solution resulted in the activation of a current whose reversal potential shifted to the right by 51 +/- 5.2 mV when Cl- in the pipette solution was lowered from 119.3 to 10 mM. No currents were generated when Ca2+ was omitted from the solution. The current is therefore a Ca(2+)-activated Cl- one. 3. Following exposure to Ca2+, the half-time for activation of ICl,Ca was not voltage dependent, whereas deactivation was strongly so. 4. ICl,Ca was stable in the continuous presence of Ca2+ and showed no sign of inactivation or adaptation. 5. Comparison of the size of the currents (normalized to pipette resistance) from the animal and vegetal poles revealed that ICl,Ca had a highly polarized distribution. The current density was almost 10 times higher in the animal pole. 6. The results suggest that Cl- channels provide a continuous and reliable indication of submembranous Ca2+, at least in an excised patch, and the clustering of the Cl- channels renders it necessary to exert caution in interpreting results involving the kinetics of Ca2+ signalling, when ICl,Ca is used as the sole monitor of calcium.
authors.affiliation: Max-Planck-Institute for Experimental Medicine, Göttingen, Germany.
authors.forename: J M
authors.initials: JM
authors.lastname: Gomez-Hernandez
authors.forename: W
authors.initials: W
authors.lastname: Stühmer
authors.forename: A B
authors.initials: AB
authors.lastname: Parekh
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology* / Q000502:physiology; D018118:Chloride Channels / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects*; D007700:Kinetics; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D018118:Chloride Channels; D002118:Calcium