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A cytoplasmic factor, calpastatin and ATP together reverse run-down of Ca2+ channel activity in guinea-pig heart

L Y Hao1, A Kameyama, M Kameyama

  • 1Department of Physiology, Faculty of Medicine, Kagoshima University, Kagoshima 890-8520, Japan.

The Journal of Physiology
|January 12, 1999
PubMed

Insights

Cytoplasmic factors, including a protein-like component (H fraction) and calpastatin, along with ATP, are crucial for maintaining L-type Ca2+ channel activity and reversing run-down in heart cells.

Area of Science:

  • Cardiovascular Physiology
  • Molecular Biology
  • Cellular Signaling

Background:

  • L-type Ca2+ channels are critical for cardiac function.
  • Channel activity can decrease over time (run-down) during experimental procedures.
  • Identifying factors that regulate channel activity is essential for understanding cardiac electrophysiology.

Purpose of the Study:

  • To investigate the role of cytoplasmic factors in maintaining L-type Ca2+ channel activity.
  • To identify specific components responsible for preventing or reversing channel run-down.
  • To elucidate the mechanisms underlying the regulation of Ca2+ channel basal activity.

Main Methods:

  • Cytoplasmic extract from bovine heart was fractionated using gel filtration.
  • Effects of fractions on L-type Ca2+ channel activity were assessed in guinea-pig ventricular myocytes using patch-clamp techniques.
  • Run-down was induced, and the ability of fractions, calpastatin, and ATP to restore channel activity was evaluated.
  • Protein characteristics (heat and trypsin sensitivity) and involvement of specific kinases/phosphatases were examined.

Main Results:

  • Cytoplasmic fractions (H and P) and ATP partially restored Ca2+ channel activity after run-down.
  • A combination of H fraction, P fraction, and ATP maximally restored channel activity (86%).
  • Calpastatin mimicked the restorative effect of the P fraction, and its combination with H fraction and ATP provided sustained channel activity.
  • The effective component in the H fraction exhibited protein-like properties, and known kinases/phosphatases were not identified as the active components.

Conclusions:

  • Basal activity of L-type Ca2+ channels is maintained by at least three factors: a protein-like factor in the H fraction, calpastatin, and ATP.
  • These factors play a significant role in preventing or reversing channel run-down.
  • The findings provide insights into the complex regulation of cardiac ion channel function.

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