Ca(2+)-dependent activation of Cl(-) currents in Xenopus oocytes is modulated by voltage.
Ca(2+)-activated Cl(-) currents (I(Cl,Ca)) were examined using fluorescence confocal microscopy to monitor intracellular Ca(2+) liberation evoked by flash photolysis of caged inositol 1,4, 5-trisphosphate (InsP(3)) in voltage-clamped Xenopus oocytes. Currents at +40 mV exhibited a steep dependence on InsP(3) concentration ([InsP(3)]), whereas currents at -140 mV exhibited a higher threshold and more graded relationship with [InsP(3)]. Ca(2+) levels required to half-maximally activate I(Cl,Ca) were about 50% larger at -140 mV than at +40 mV, and currents evoked by small Ca(2+) elevations were reduced >25-fold. The half-decay time of Ca(2+) signals shortened at increasingly positive potentials, whereas the decay of I(Cl,Ca) lengthened. The steady-state current-voltage (I-V) relationship for I(Cl,Ca) exhibited outward rectification with weak photolysis flashes but became more linear with stronger stimuli. Instantaneous I-V relationships were linear with both strong and weak stimuli. Current relaxations following voltage steps during activation of I(Cl,Ca) decayed with half-times that shortened from about 100 ms at +10 mV to 20 ms at -160 mV. We conclude that InsP(3)-mediated Ca(2+) liberation activates a single population of Cl(-) channels, which exhibit voltage-dependent Ca(2+) activation and voltage-independent instantaneous conductance.
Callamaras
N
N
Laboratory of Cellular and Molecular Neurobiology, Department of Neurobiology and Behavior, University of California Irvine, Irvine, California 92697-4550, USA.
Parker
I
I
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D005453:Fluorescence; D006706:Homeostasis; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000502:physiology; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010782:Photolysis; D014982:Xenopus laevis
D018118:Chloride Channels; C061868:inositol 1,4,5-trisphosphate 1-(2-nitrophenyl)ethyl ester; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium