Na+/Ca2+ exchange currents and SR Ca2+ contents in postinfarction myocytes

Xue Qian Zhang, Douglas L. Tillotson, Russell L. Moore, R. Zelis, Joseph Y. Cheung

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Abstract

Myocytes isolated from rat hearts 3 wk after myocardial infarction (MI) had lower peak cytosolic free Ca2+ concentration ([Ca2+]i) and reduced maximal extent of cell shortening during contraction, but Ca2+ entry via L-type Ca2+ channels was normal. In the current study using whole cell patchclamp technique, reverse Na+/Ca2+ exchange current (INa/ca; 3 Na+ out:1Ca2+ in) was measured in myocytes in which Na+, K+, and Ca2+ currents were blocked or minimized. Steady-state outward currents measured under these conditions increased with depolarization or with elevation of extracellular Ca2+ concentration ([Ca2+]o) from 1.8 to 5.0 mM, but were inhibited by 5 mM Ni2+ or by reduction of [Ca2+]i to near zero. In addition, reduction of cytosolic free Na+ concentration or of [Ca2+]i also decreased the amplitude of the outward current. These characteristics indicate the outward current was INa/Ca operating in reverse mode. Reverse INa/Ca was significantly lower in MI myocytes, especially at more positive voltages. In addition, sarcoplasmic reticulum (SR)-releasable Ca2+ content as estimated by integrating forward INa/Ca during caffeine-induced SR Ca2+ release was also significantly lower in MI myocytes. Depressed Na+/Ca2+ exchange activity may contribute to abnormal [Ca2+]i dynamics in MI myocytes.

Original languageEnglish (US)
Pages (from-to)C1800-C1807
JournalAmerican Journal of Physiology
Volume271
Issue number6 PART 1
DOIs
StatePublished - 1996

All Science Journal Classification (ASJC) codes

  • Physiology (medical)

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