Volume exclusion in calcium selective channels

¹ University of Pannonia
² Miller School of Medicine, University of Miami,
³ Brigham Young University
⁴ Rush Medical Center
⁵ Rush University Medical Center

^* To whom correspondence should be addressed. E-mail: beisenbe{at}rush.edu.

Submitted on September 25, 2007
Revised on November 29, 2007
Accepted on 18 December 2007

	Abstract

Corry, Chung and their associates have proposed an interesting model for calcium channel selectivity. However, on the basis of their reported results we find it impossible to assess the merits of their model because their results and claims concerning selectivity are based on an extrapolation over four orders of magnitude to low Ca²⁺ concentration. Their results and claims have been presented in several articles and reviews in several journals and, thus, need attention. In this paper, we first establish that we obtain results on electrostatics and channel occupancies similar to the high-concentration simulations they present. We then perform grand canonical ensemble simulations that enable us to study micromolar Ca²⁺ concentrations. We find that their model channel is only weakly Ca²⁺ selective. A crucial problem with their model appears to be the placement of the negatively charged glutamate structural elements in fixed positions inside the protein rather than as flexible units inside the filter.

Key Words: Calcium channel, Monte Carlo, selectivity

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