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Decrease with senescence in the norepinephrine-induced phosphorylation of myofilament proteins in isolated rat

M Sakai1, R S Danziger, J M Staddon

  • 1Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.

Journal of Molecular and Cellular Cardiology
|December 1, 1989
PubMed
Summary

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Norepinephrine

Area of Science:

  • Cardiovascular physiology
  • Molecular biology
  • Gerontology

Background:

  • Cardiac function is modulated by protein phosphorylation.
  • Aging affects cellular signaling pathways.
  • Norepinephrine is a key neurotransmitter in cardiac regulation.

Purpose of the Study:

  • To investigate the impact of aging on norepinephrine-induced protein phosphorylation in rat cardiac myocytes.
  • To elucidate the role of cyclic AMP signaling in age-related changes in cardiac protein phosphorylation.

Main Methods:

  • Isolated rat cardiac ventricular myocytes from young and senescent rats were used.
  • Autoradiography and electrophoresis were employed to quantify 32P-labeled protein phosphorylation.
  • Forskolin, 8-(4-chlorophenylthio) cyclic AMP, and isobutylmethylxanthine were used to probe signaling pathways.

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Main Results:

  • Norepinephrine-induced phosphorylation of troponin I and C-protein was significantly reduced in senescent rat myocytes compared to young myocytes.
  • Age-associated decrements in phosphorylation were attenuated by direct adenylate cyclase activators and cyclic AMP analogs.
  • Dephosphorylation rates of troponin I remained unchanged with age, indicating intact protein phosphatase activity.
  • Isobutylmethylxanthine abolished age-associated differences in protein phosphorylation.

Conclusions:

  • Senescent heart cells exhibit diminished cyclic AMP formation in response to norepinephrine.
  • Reduced cyclic AMP signaling leads to decreased activation of protein kinase A and subsequent impaired phosphorylation of target proteins.
  • Aging impairs the norepinephrine-mediated signaling cascade upstream of protein kinase A in cardiac myocytes.