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This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 296/6/H1994    most recent 00038.2009v1 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 Janowski, E. Articles by Morad, M. PubMed PubMed Citation Articles by Janowski, E. Articles by Morad, M.

β-Adrenergic regulation of a novel isoform of NCX: sequence and expression of shark heart NCX in human kidney cells

¹Medical University of South Carolina, Charleston, South Carolina; ²Georgetown University, Washington, DC; ³Uniformed Services University of the Health Sciences, Bethesda, Maryland; ⁴Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada; and ⁵Mount Desert Island Biological Laboratory, Salsbury Cove, Maine

Submitted 12 January 2009 ; accepted in final form 18 April 2009

The function, regulation, and molecular structure of the cardiac Na⁺/Ca²⁺ exchangers (NCXs) vary significantly among vertebrates. We previously reported that β-adrenergic suppression of amphibian cardiac NCX1.1 is associated with specific molecular motifs. Here we investigated the bimodal, cAMP-dependent regulation of spiny dogfish shark (Squalus acanthias) cardiac NCX, exploring the effects of molecular structure, host cell environment, and ionic milieu. The shark cardiac NCX sequence (GenBank accession no. DQ 068478) revealed two novel proline/alanine-rich amino acid insertions. Wild-type and mutant shark NCXs were cloned and expressed in mammalian cells (HEK-293 and FlpIn-293), where their activities were measured as Ni²⁺-sensitive Ca²⁺ fluxes (fluo 4) and membrane (Na⁺/Ca²⁺ exchange) currents evoked by changes in extracellular Na⁺ concentration and/or membrane potential. Regardless of Ca²⁺ buffering, β-adrenergic stimulation of cloned wild-type shark NCX consistently produced bimodal regulation (defined as differential regulation of Ca²⁺-efflux and -influx pathways), with suppression of the Ca²⁺-influx mode and either no change or enhancement of the Ca²⁺-efflux mode, closely resembling results from parallel experiments with native shark cardiomyocytes. In contrast, mutant shark NCX, with deletion of the novel region 2 insertion, produced equal suppression of the inward and outward currents and Ca²⁺ fluxes, thereby abolishing the bimodal nature of the regulation. Control experiments with nontransfected and dog cardiac NCX-expressing cells showed no cAMP regulation. We conclude that bimodal β-adrenergic regulation is retained in cloned shark NCX and is dependent on the shark's unique molecular motifs.

sodium/calcium exchanger; cAMP; bimodal regulation; cloning; cardiac electrophysiology