Changes in contractile force by barium in the frog skeletal muscle

Area of Science:

• Muscle Physiology
• Ion Channel Pharmacology

Background:

• Barium ions (Ba2+) are known to affect cellular electrophysiology.
• Skeletal muscle contractility is dependent on calcium ion (Ca2+) dynamics.

Purpose of the Study:

• To investigate the effects of Ba2+ on frog skeletal muscle contractility.
• To elucidate the role of Ba2+ in modulating membrane potential and mechanical responses.

Main Methods:

• Current clamp recordings in frog skeletal muscle.
• Perfusion with Ba2+ solutions.
• Assessment of electrically induced contractures and twitches.
• Experiments in the presence of tetrodotoxin (TTX) and varying Ca2+ concentrations.

Main Results:

• Ba2+ (2 mM) caused membrane depolarization (10-20 mV) and altered membrane resistance.
• Ba2+ shifted the mechanical threshold to more positive potentials.
• Ba2+ enhanced both electrically induced contractures (in TTX) and normal twitches.
• An afterpotentiation was observed upon Ba2+ washout, suggesting an underlying inhibition.
• Ba2+ potentiated caffeine-induced contractures more effectively than Ca2+ in low Ca2+ conditions, likely via sarcoplasmic reticulum Ca2+ release, while Mg2+ inhibited it.

Conclusions:

• Ba2+ significantly influences frog skeletal muscle excitability and contractility.
• Ba2+ exerts both potentiating and inhibitory effects on muscle contraction.
• Ba2+ plays a role in calcium release from the sarcoplasmic reticulum, impacting contracture tension.