Electrical decoupling by Sr action potentials in guinea-pig papillary muscle

Area of Science:

• Cardiac Electrophysiology
• Membrane Biophysics
• Muscle Physiology

Background:

• Understanding cardiac muscle electrophysiology is crucial for diagnosing and treating heart conditions.
• Membrane constants, such as longitudinal resistance, are key determinants of cardiac action potential propagation.
• The role of specific ions like strontium (Sr2+) in modulating these constants requires further investigation.

Purpose of the Study:

• To investigate the impact of strontium (Sr2+) on the membrane constants of guinea-pig papillary muscle.
• To analyze the relationship between changes in longitudinal resistance (ri) and action potential conduction velocity.
• To explore the underlying mechanisms of Sr2+-induced electrophysiological alterations.

Main Methods:

• Cable analysis of guinea-pig papillary muscle.
• Utilized a single sucrose gap and micro-electrode recordings.
• Performed perfusions with Na-free and Na-containing Sr Tyrode solutions.

Main Results:

• In Na-free 20 mmol/l Sr Tyrode, longitudinal resistance (ri) increased by 210% (10 action potentials) and 457% (20 action potentials).
• This increase in ri was reversible upon perfusion with Na-containing solutions and absent in Na-containing Sr Tyrode.
• Conduction velocity decreased from 8.6 to 3.1 cm/s, and muscle relaxation slowed significantly in Na-free Sr Tyrode.

Conclusions:

• Sr2+ significantly increases longitudinal resistance (ri) in cardiac muscle, likely due to junctional decoupling.
• The observed increase in ri is associated with reduced action potential conduction velocity and impaired muscle relaxation.
• Junctional decoupling may result from intracellular Sr2+ accumulation or increased intracellular H+.