Linear electrical properties of isolated cardiac cells

Area of Science:

• Cellular electrophysiology
• Membrane biophysics

Background:

• Isolated ventricular cells exhibit complex electrical properties.
• Understanding internal membrane capacitance is crucial for cardiac electrophysiology.

Purpose of the Study:

• To identify the cellular structures responsible for the large internal membrane capacitance in ventricular cells.
• To investigate the role of the sarcoplasmic reticulum and transverse tubular system in cellular capacitance and access resistance.

Main Methods:

• Frequency domain equivalent circuit analysis of isolated ventricular cells.
• Measurements in hypertonic solutions to assess membrane capacitance and access resistance.
• Freeze-fractured electron microscopy to study cellular structures.

Main Results:

• An internal membrane capacitance four- to sixfold larger than the surface membrane was detected.
• The sarcoplasmic reticulum is the primary contributor to this internal capacitance due to its large surface area.
• Access resistance to the internal membrane increased with hypertonicity, implicating the dyadic junction.

Conclusions:

• The sarcoplasmic reticulum is the main source of internal membrane capacitance in ventricular cells.
• The dyadic junction likely provides the electrical coupling between the sarcoplasmic reticulum and the surface membrane.
• These findings enhance our understanding of cardiac cell electrophysiology.