Plasmalemmal calcium in cardiac excitation-contraction coupling

Area of Science:

• Cardiology
• Cell Physiology
• Biophysics

Background:

• Mammalian heart muscle exhibits extreme sensitivity to external calcium concentration, with immediate force adaptation.
• Mammalian cardiac cells possess extensive transverse tubules that significantly increase surface area.

Purpose of the Study:

• To investigate the role of external calcium concentration in mammalian heart muscle contractility.
• To explore the mechanism of excitation-contraction coupling involving calcium and cardiac cell membranes.

Main Methods:

• Experimental investigation of cardiac muscle response to varying external calcium concentrations.
• Analysis of the proposed excitation-contraction coupling mechanism based on physicochemical interactions.

Main Results:

• Heart muscle force directly and immediately adapts to changes in external calcium.
• Evidence suggests a superficial calcium fraction on the plasmalemma is involved in excitation-contraction coupling.
• The interaction of calcium with membrane phospholipids is modulated by electric fields and proton activity.

Conclusions:

• External calcium concentration is a critical determinant of mammalian cardiac contractility.
• A physicochemical interaction model involving calcium and membrane phospholipids explains excitation-contraction coupling.