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Am J Physiol Cell Physiol (November 14, 2001). doi:10.1152/ajpcell.00443.2001
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Articles in PresS, published online ahead of print November 13, 2001
Am J Physiol Cell Physiol, 10.1152/ajpcell.00443.2001
Submitted on September 14, 2001
Accepted on November 8, 2001

The role of aspartate residues in Ca2+ affinity and permeation of the distal ECaC1 channel

Karine Jean1, Gerald Bernatchez1, Helene Klein1, Line Garneau1, Remy Sauve1, and Lucie Parent1*

1 Physiologie, Universite de Montreal, Montreal, Quebec, Canada

* To whom correspondence should be addressed. E-mail: lucie.parent{at}umontreal.ca.

The Ca2+ -affinity and -permeation of the ECaC1 channel were investigated after expression in Xenopus oocytes. ECaC1 displays anomalous mole-fraction effects. Extracellular Ca2+ and Mg2+ reversibly inhibited ECaC1 whole-cell Li+ currents with IC50 = 2.2 ± 0.4 µM (9) and 235 ± 35 µM (10) respectively. These values compare well to CaV1.2 measured under the same conditions suggesting that high-affinity Ca2+ binding is a well-conserved feature among of non- and voltage-gated Ca2+ channels. Neutralization of D550 and E535Q in the pore region had no significant effect on Ca2+ and Mg2+ affinities. In contrast, neutralization of D542 significantly decreased Ca2+- affinity with IC50 = 1.1 ± 0.2 mM (6) and Mg2+ -affinity with IC50 > 25 ± 3 mM (4). Ca2+ whole-cell conductance through D542N channels, as well as the large Ca2+/Ba2+ conductance ratio, were nonetheless comparable to the wild-type ECaC1 despite a 1000-fold decrease in Ca2+ affinity. Altogether, our observations suggest that D542 plays a critical role in Ca2+ -affinity but not in Ca2+ -permeation in ECaC1.




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