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This Article Full Text Full Text (PDF) All Versions of this Article: 290/5/H2155    most recent 00958.2005v1 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 Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Hurtado, C. Articles by Pierce, G. N. Search for Related Content PubMed PubMed Citation Articles by Hurtado, C. Articles by Pierce, G. N.

Cells expressing unique Na⁺/Ca²⁺ exchange (NCX1) splice variants exhibit different susceptibilities to Ca²⁺ overload

¹Division of Stroke and Vascular Disease and ³Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre, and ²Departments of Physiology and Biochemistry and Medical Genetics, Faculties of Medicine and ⁴Pharmacy, University of Manitoba, Winnipeg, Manitoba, Canada

Submitted 8 September 2005 ; accepted in final form 20 December 2005

The Na⁺/Ca²⁺ exchanger (NCX) NCX1 exhibits tissue-specific alternative splicing. Such NCX splice variants as NCX1.1 and NCX1.3 are also differentially regulated by Na⁺ and Ca²⁺, although the physiological implications of these regulatory characteristics are unclear. On the basis of their distinct regulatory profiles, we hypothesized that cells expressing these different splice variants might exhibit unique responses to conditions promoting Ca²⁺ overload, such as during exposure to cardiac glycosides or simulated ischemia. NCX1.1 or NCX1.3 was expressed in human embryonic kidney (HEK)-293 cells or rat neonatal ventricular cardiomyocytes (NVC), and expression was confirmed by Western blotting and immunocytochemical analyses. HEK-293 cells lacked NCX1 protein before transfection. With use of adenoviral vectors, neonatal cardiomyocytes were induced to overexpress the NCX1.1 splice variant by nearly twofold, whereas the NCX1.3 isoform was expressed on the endogenous NCX1.1 background. Total expression was comparable for NCX1.1 and NCX1.3. Exposure of NVC to ouabain induced a significant increase in cellular Ca²⁺, an effect that was exaggerated in cells overexpressing NCX1.1, but not NCX1.3. The increase in intracellular Ca²⁺ was inhibited by 5 µM KB-R7943. Cardiomyocytes overexpressing NCX1.1 also exhibited a greater accumulation of intracellular Ca²⁺ in response to simulated ischemia than did cells expressing NCX1.3. Similar responses were observed in HEK-293 cells where NCX1.1 was expressed. We conclude that expression of the NCX1.3 splice variant protects against severe Ca²⁺ overload, whereas NCX1.1 promotes Ca²⁺ overload in response to cardiac glycosides and ischemic challenges. These results highlight the importance of ionic regulation in controlling NCX1 activity under conditions that promote Ca²⁺ overload.

NCX1.1; NCX1.3; ouabain; ischemia

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