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Am J Physiol Cell Physiol 282: C665-C672, 2002. First published November 14, 2001; doi:10.1152/ajpcell.00443.2001
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Vol. 282, Issue 4, C665-C672, April 2002

Role of aspartate residues in Ca2+ affinity and permeation of the distal ECaC1

K. Jean, G. Bernatchez, H. Klein, L. Garneau, R. Sauvé, and L. Parent

Groupe de Recherche en Transport Membranaire, Département de Physiologie, Université de Montréal, Montreal, Quebec, Canada H3C 3J7

The Ca2+ affinity and permeation of the epithelial Ca2+ channel (ECaC1) were investigated after expression in Xenopus oocytes. ECaC1 displayed anomalous mole-fraction effects. Extracellular Ca2+ and Mg2+ reversibly inhibited ECaC1 whole cell Li+ currents: IC50 = 2.2 ± 0.4 µM (n = 9) and 235 ± 35 µM (n = 10), respectively. These values compare well with the Ca2+ affinity of the L-type voltage-gated Ca2+ (CaV1.2) channel measured under the same conditions, suggesting that high-affinity Ca2+ binding is a well-conserved feature of epithelial and voltage-gated Ca2+ channels. Neutralization of D550 and E535 in the pore region had no significant effect on Ca2+ and Mg2+ affinities. In contrast, neutralization of D542 significantly decreased Ca2+ affinity (IC50 = 1.1 ± 0.2 mM, n = 6) and Mg2+ affinity (IC50 > 25 ± 3 mM, n = 4). Despite a 1,000-fold decrease in Ca2+ affinity in D542N, Ca2+ permeation properties and the Ca2+-to-Ba2+ conductance ratio remained comparable to values for wild-type ECaC1. Together, our observations suggest that D542 plays a critical role in Ca2+ affinity but not in Ca2+ permeation in ECaC1.

Xenopus oocytes; structure function; site-directed mutagenesis; single channel; distal tubule; kidney; selectivity


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