HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 100/4/2115    most recent 90473.2008v2 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Rodriguez-Contreras, A. Articles by Yamoah, E. N. PubMed PubMed Citation Articles by Rodriguez-Contreras, A. Articles by Yamoah, E. N.

Effects of Strontium on the Permeation and Gating Phenotype of Calcium Channels in Hair Cells

¹Center for Neuroscience, Program in Communication Sciences, University of California, Davis, California; and ²Department of Nephrology, Xijing Hospital, Fourth Military Medical University, Xi'an, China

Submitted 15 April 2008; accepted in final form 30 July 2008

To minimize the effects of Ca²⁺ buffering and signaling, this study sought to examine single Ca²⁺ channel properties using Sr²⁺ ions, which substitute well for Ca²⁺ but bind weakly to intracellular Ca²⁺ buffers. Two single-channel fluctuations were distinguished by their sensitivity to dihydropyridine agonist (L-type) and insensitivity toward dihydropyridine antagonist (non-L-type). The L- and non-L-type single channels were observed with single-channel conductances of 16 and 19 pS at 70 mM Sr²⁺ and 11 and 13 pS at 5 mM Sr²⁺, respectively. We obtained K_D estimates of 5.2 and 1.9 mM for Sr²⁺ for L- and non-L-type channels, respectively. At Ca²⁺ concentration of 2 mM, the single-channel conductances of Sr²⁺ for the L-type channel was 1.5 and 4.0 pS for the non-L-type channels. Thus the limits of single-channel microdomain at the membrane potential of a hair cell (e.g., –65 mV) for Sr²⁺ ranges from 800 to 2,000 ion/ms, assuming an E_Ca of 100 mV. The channels are 4-fold more sensitive at the physiological concentration ranges than at concentrations >10 mM. Additionally, the channels have the propensity to dwell in the closed state at high concentrations of Sr²⁺, which is reflected in the time constant of the first latency distributions. It is concluded that the concentration of the permeant ion modulates the gating of hair cell Ca²⁺ channels. Finally, the closed state/s that is/are altered by high concentrations of Sr²⁺ may represent divalent ion-dependent inactivation of the L-type channel.