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Inactivation of Ca current during the action potential in guinea-pig ventricular myocytes

E White1, D A Terrar

  • 1University Department of Pharmacology, Oxford.

Experimental Physiology
|January 1, 1992
PubMed

Insights

Calcium channel inactivation in guinea-pig heart cells was studied. Results show voltage and intracellular calcium influence inactivation during the action potential plateau, with recovery near repolarization.

Area of Science:

  • Cardiology
  • Cell Physiology
  • Electrophysiology

Background:

  • Cardiac action potentials rely on calcium (Ca) channel function.
  • Understanding Ca channel behavior during the action potential plateau is crucial for cardiac health.

Purpose of the Study:

  • To investigate the mechanisms of Ca channel inactivation during the action potential plateau in guinea-pig ventricular myocytes.
  • To determine the roles of voltage and intracellular calcium in this process.

Main Methods:

  • Action potentials were interrupted with voltage clamp pulses to measure Ca channel availability.
  • The effect of intracellular calcium was assessed using the Ca chelator BAPTA.

Main Results:

  • Ca channel availability decreased with action potential duration, nearing zero at the plateau end.
  • Availability increased when membrane potential became more negative than -40 mV.
  • BAPTA loading increased Ca channel availability, but inactivation persisted, suggesting dual mechanisms.

Conclusions:

  • The majority of Ca channels inactivate during the action potential plateau in guinea-pig ventricular myocytes.
  • Both voltage-dependent and Ca-induced inactivation contribute significantly to this process.
  • Ca channel recovery is largely complete only near the end of repolarization.

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