Related Experiment Videos
Changes in membrane currents in bullfrog atrium produced by acetylcholine.
The Journal of Physiology
|September 1, 1976
Summary
Acetylcholine significantly reduces the slow inward calcium/sodium current in bullfrog atrial muscle, explaining its negative inotropic effect. It also increases potassium-based background current, but this does not account for the reduced calcium entry.
Area of Science:
- Cardiovascular Physiology
- Electrophysiology
- Pharmacology
Background:
- Acetylcholine mediates negative inotropic effects in cardiac muscle.
- The precise ionic mechanisms underlying acetylcholine's action on atrial electrophysiology require further elucidation.
Purpose of the Study:
- To investigate the effects of acetylcholine on membrane currents in bullfrog atrial trabeculae.
- To clarify the ionic basis for acetylcholine's negative inotropic action.
Main Methods:
- Double sucrose-gap voltage-clamp technique.
- Pharmacological manipulations to isolate specific ionic currents.
Main Results:
- Acetylcholine ( > 2.0 x 10(-8)M) markedly reduced the slow inward (Ca2+/Na+) current.
- High acetylcholine doses ( ~ 10(-7)M) decreased membrane resistance by increasing a time-independent K+ background current.
- The reduction in slow inward current preceded significant increases in background current, and the background current did not fully explain the reduction.
Conclusions:
- Reduced net calcium entry due to decreased slow inward current explains acetylcholine's negative inotropic effect.
- Acetylcholine's effects on atrial membrane currents involve both modulation of the slow inward current and an increase in K+ background current.