Slow membrane potential changes in skeletal muscle induced in Cl(-)-free medium

Area of Science:

• Muscle Physiology
• Electrophysiology
• Ion Channel Function

Background:

• Myotonic muscles exhibit electrical instability, a phenomenon not fully understood at the ionic level.
• Understanding ion channel dynamics during muscle excitation is crucial for addressing muscle disorders.

Purpose of the Study:

• To investigate the ionic mechanisms underlying slow transient depolarizations in muscles.
• To explore the role of potassium and calcium conductances in muscle electrical activity.
• To assess the impact of external potassium concentration on these electrical events.

Main Methods:

• Conventional microelectrode techniques were employed to measure membrane potential (Vm) and conductance (Gm).
• Experiments were conducted on muscles in a chloride-free solution with tetraethylammonium (TEA+).
• Stimulation protocols included electrical impulses and stepwise elevation of external potassium ([K+]0).

Main Results:

• Electrical stimulation induced slow depolarizations (slow response) associated with increased calcium conductance.
• Potassium conductance initially increased then decreased during the slow response.
• Elevating [K+]0 during the slow response resulted in significant repolarization and increased Gm.
• Tetrodotoxin did not affect the slow response or K+-induced changes, but nifedipine abolished the slow response.

Conclusions:

• The slow response involves increased calcium conductance and reduced inward rectifier potassium channel conductance.
• [K+]0 elevation can restore inward rectifier potassium channel function during the slow response.
• These ionic mechanisms may contribute to the electrical instability observed in myotonic muscles, with potential therapeutic implications.