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Altered calcium handling in compensated hypertrophied rat cardiomyocytes induced by pressure overload.

Authors
  • Sumida, E
  • Nohara, M
  • Muro, A
  • Sumida, E
  • Kaku, H
  • Koga, Y
  • Toshima, H
  • Imaizumi, T
Type
Published Article
Journal
Japanese circulation journal
Publication Date
Jan 01, 1998
Volume
62
Issue
1
Pages
36–46
Identifiers
PMID: 9559416
Source
Medline
License
Unknown

Abstract

To investigate Ca2+ handling in compensated hypertrophied cardiomyocytes, we measured Ca2+ transients and contraction of hypertrophied rat left ventricular myocytes induced by aortic constriction (AC). The fluorescence ratio (I405/I480) after indo-1/AM loading and circumferential length were simultaneously measured in isolated myocytes. The amplitude of Ca2+ transients (Ca-Amp) was higher in rats with AC than in sham-operated rats (Sham) (0.25 +/- 0.08 vs 0.17 +/- 0.05). There was a positive correlation between Ca-Amp and fractional shortening (FS) in both AC and Sham rats, whereas the ratio of FS/Ca-Amp was smaller in AC rats. These observations suggest that compensated hypertrophied cardiomyocytes exhibit an adaptive increase in Ca-Amp, associated with reduced myofilament responsiveness to an increase in Ca2+. Isoproterenol and forskolin increased Ca-Amp and FS, and decreased time to 50% decline of Ca2+ transients. Although myocytes from AC rats exhibited reduced responsiveness to isoproterenol, responses to forskolin did not differ between the 2 groups. The reduced beta-adrenergic response in Ca2+ handling was probably due to altered beta-adrenoceptor numbers, G-protein function and/or their coupling process.

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