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Am J Physiol Heart Circ Physiol 283: H1616-H1626, 2002. First published June 27, 2002; doi:10.1152/ajpheart.00186.2002
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Vol. 283, Issue 4, H1616-H1626, October 2002

Effects of Na+/Ca2+ exchanger downregulation on contractility and [Ca2+]i transients in adult rat myocytes

George M. Tadros2,*, Xue-Qian Zhang1,*, Jianliang Song1, Lois L. Carl1, Lawrence I. Rothblum1, Qiang Tian1, Jeremy Dunn3, Jonathan Lytton3, and Joseph Y. Cheung1,2

1 Weis Center for Research and 2 Department of Medicine, Geisinger Medical Center, Danville, Pennsylvania 17822; and 3 Department of Biochemistry and Molecular Biology, University of Calgary Health Sciences Center, Calgary, Alberta, Canada T2N 4N1

Postmyocardial infarction (MI) rat myocytes demonstrated depressed Na+/Ca2+ exchange (NCX1) activity, altered contractility, and intracellular Ca2+ concentration ([Ca2+]i) transients. We investigated whether NCX1 downregulation in normal myocytes resulted in contractility changes observed in MI myocytes. Myocytes infected with adenovirus expressing antisense (AS) oligonucleotides to NCX1 had 30% less NCX1 at 3 days and 66% less NCX1 at 6 days. The half-time of relaxation from caffeine-induced contracture was twice as long in ASNCX1 myocytes. Sarcoplasmic reticulum (SR) Ca2+-ATPase abundance, SR Ca2+ uptake, resting membrane potential, action potential amplitude and duration, L-type Ca2+ current density and cell size were not affected by ASNCX1 treatment. At extracellular Ca2+ concentration ([Ca2+]o) of 5 mM, ASNCX1 myocytes had significantly lower contraction and [Ca2+]i transient amplitudes and SR Ca2+ contents than control myocytes. At 0.6 mM [Ca2+]o, contraction and [Ca2+]i transient amplitudes and SR Ca2+ contents were significantly higher in ASNCX1 myocytes. At 1.8 mM [Ca2+]o, contraction and [Ca2+]i transient amplitudes were not different between control and ASNCX1 myocytes. This pattern of contractile and [Ca2+]i transient abnormalities in ASNCX1 myocytes mimics that observed in rat MI myocytes. We conclude that downregulation of NCX1 in adult rat myocytes resulted in decreases in both Ca2+ influx and efflux during a twitch. We suggest that depressed NCX1 activity may partly account for the contractile abnormalities after MI.

excitation-contraction coupling; fura 2; primary cardiac myocyte culture; sarco(endo)plasmic reticulum Ca2+-ATPase; calsequestrin; patch clamp

* G. M. Tadros and X.-Q. Zhang contributed equally to this study.




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