Enhanced Na+-Ca2+ exchange activity in cardiomyopathic Syrian hamster

S. N. Hatem, J. S.K. Sham, M. Morad

Research output: Contribution to journalArticle

Abstract

The signaling of contraction by Ca2+ in the Syrian hamster (BIO 14.6) heart in the late stage of the cardiomyopathy (220 to 300 days old) was compared with that in age-matched healthy hamster hearts. Membrane current and cell shortening or intracellular Ca2+ transients were measured simultaneously in isolated whole-cell-clamped myocytes. The density of the L- type Ca2+ current was smaller in myopathic than in normal myocytes (2.13±0.3 versus 3.21±0.4 pA/pF at 0 mV, P<.05). In both control and myopathic myocytes, the L-type Ca2+ current gated the release of Ca2+ and activation of contraction. In myopathic myocytes, activation of contraction also activated a slowly inactivating inward current of 1.73±0.2 pA/pF. The Na+-Ca2+ exchanger generated this current (I(Na-Ca)), because it was suppressed by rapid replacement of Na+ with Li+ and depletion of the intracellular Ca2+ pool by caffeine. I(Na-Ca), activated by rapid application of caffeine, was not significantly different in both groups (3.7±0.5 pA/pF in control hearts versus 3.9±0.5 pA/pF in cardiomyopathic hearts). The activation of the inward exchanger current in myopathic myocytes coincided with a significant prolongation of contraction and the intracellular Ca2+ transient and a delay in the onset of relaxation. These results suggest that the enhanced activity of the Na+-Ca2+ exchanger may be related to compromised sequestration of Ca2+ in these animals.

Original languageEnglish (US)
Pages (from-to)253-261
Number of pages9
JournalCirculation research
Volume74
Issue number2
DOIs
StatePublished - 1994

Keywords

  • Ca transients
  • Na-Ca exchange
  • cardiomyopathy

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine

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