Slow channel kinetics in heart muscle

Area of Science:

• Cardiology
• Ion Channel Physiology
• Biophysics

Background:

• The cardiac slow inward current (Isi) is critical for cardiac action potentials.
• Isi is mediated by a specific conductance system known as the slow channel.
• The slow channel exhibits high selectivity for divalent cations like Ca2+ and Sr2+, with minimal Na+ permeability.

Purpose of the Study:

• To investigate the voltage- and temperature-sensitivity of slow channel kinetics.
• To explore the inactivation and recovery processes of the cardiac slow channel.
• To determine if a single inactivation variable adequately describes slow channel behavior.

Main Methods:

• Electrophysiological recordings in cat ventricular myocardium.
• Analysis of activation, inactivation, and recovery kinetics.
• Comparison with the Hodgkin-Huxley model framework.

Main Results:

• Isi kinetics are sensitive to voltage and temperature.
• Inactivation and recovery from inactivation exhibit different time constants.
• Pharmacological differences in inactivation and recovery suggest distinct mechanisms.
• A second inactivation variable is necessary to model slow channel behavior.

Conclusions:

• Cardiac slow channels display complex inactivation kinetics.
• A novel slow inactivation process exists in cardiac slow channels.
• The findings necessitate modifications to existing models of cardiac ion channel function.