The epithelial calcium channel, ECaC, is activated by hyperpolarization and regulated by cytosolic calcium. |
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Authors: | J G Hoenderop A W van der Kemp A Hartog C H van Os P H Willems R J Bindels |
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Institution: | Department of Cell Physiology, Institute of Cellular Signalling, Nijmegen, 6500 HB, The Netherlands. |
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Abstract: | The recently cloned epithelial Ca(2+) channel, ECaC, which is expressed in the apical membrane of 1,25-dihydroxyvitamin D(3)-responsible epithelia, was characterized in Xenopus laevis oocytes by measuring the Ca(2+)-activated Cl(-) current which is a sensitive read-out of the Ca(2+) influx. ECaC-expressing oocytes responded to a voltage ramp with a maximal inward current of -2.1 +/- 0.3 microA at a holding potential of -99 +/- 1 mV. The inward current decreased progressively at less negative potentials and at +50 mV a small Ca(2+)-induced outward current was observed. The Ca(2+) influx-evoked current at a hyperpolarizing pulse to -100 mV displayed a fast activation followed by a rapid but partial inactivation. Loading of the oocytes with the Ca(2+) chelator BAPTA delayed the activation and blocked the inactivation of ECaC. When a series of brief hyperpolarizing pulses were given a significant decline in the peak response and subsequent plateau phase was observed. In conclusion, the distinct electrophysiological features of ECaC are hyperpolarization-dependent activation, Ca(2+)-dependent regulation of channel conductance and desensitization during repetitive stimulation. |
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