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: 575/3/693    most recent jphysiol.2006.113910v1 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 Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Urbanczyk, J. Articles by Reeves, J. P. Search for Related Content PubMed PubMed Citation Articles by Urbanczyk, J. Articles by Reeves, J. P. Related Collections Cellular

¹ Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey, Graduate School of Biomedical Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA

The activity of the cardiac Na⁺–Ca²⁺ exchanger (NCX1.1) is allosterically regulated by Ca²⁺, which binds to two acidic regions in the cytosolically disposed central hydrophilic domain of the NCX protein. A mutation in one of the regulatory Ca²⁺ binding regions (D447V) increases the half-activation constant (K_h) for allosteric Ca²⁺ activation from 0.3 to > 1.8 µM. Chinese hamster ovary cells expressing the D447V exchanger showed little or no activity under physiological ionic conditions unless cytosolic [Ca²⁺] was elevated to > 1 µM. However, when cytosolic [Na⁺] was increased to 20 mM or more (using ouabain-induced inhibition of the Na⁺,K⁺-ATPase or the ionophore gramicidin), cells expressing the D447V mutant rapidly accumulated Ca²⁺ or Ba²⁺ when the reverse (Ca²⁺ influx) mode of NCX activity was initiated, although initial cytosolic [Ca²⁺] was < 100 nM. Importantly, the time course of Ca²⁺ uptake did not display the lag phase that reflects allosteric Ca²⁺ activation of NCX activity in the wild-type NCX1.1; indeed, at elevated [Na⁺], the D447V mutant behaved similarly to the constitutively active deletion mutant (241–680), which lacks the regulatory Ca²⁺ binding sites. In cells expressing wild-type NCX1.1, increasing concentrations of cytosolic Na⁺ led to a progressive shortening of the lag phase for Ca²⁺ uptake. The effects of elevated [Na⁺] developed rapidly and were fully reversible. The activity of the D447V mutant was markedly inhibited when phosphatidylinositol 4,5-bisphosphate (PIP2) levels were reduced. We conclude that when PIP2 levels are high, elevated cytosolic [Na⁺] induces a mode of exchange activity that does not require allosteric Ca²⁺ activation.

(Received 19 May 2006; accepted after revision 23 June 2006; first published online 29 June 2006)
Corresponding author J. P. Reeves: Department of Pharmacology & Physiology, UMDNJ – NJ Medical School, 185 South Orange Avenue, PO Box 1709, Newark, NJ 07101-1709, USA. Email: reeves{at}umdnj.edu

This article has been cited by other articles:

				O. Chernysh, M. Condrescu, and J. P. Reeves Sodium-dependent inactivation of sodium/calcium exchange in transfected Chinese hamster ovary cells Am J Physiol Cell Physiol, October 1, 2008; 295(4): C872 - C882. [Abstract] [Full Text] [PDF]

				J. P. Reeves, M. Abdellatif, and M. Condrescu The sodium-calcium exchanger is a mechanosensitive transporter J. Physiol., March 15, 2008; 586(6): 1549 - 1563. [Abstract] [Full Text] [PDF]