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The effect of harmaline on membrane potentials of rat atrial contractile fibers
Abstract:
Rat atria either beating spontaneously or electrically driven were were perfused in vitro at 30 degrees C. When the preparations were exposed to harmaline 8.3 x 10(-5) or 16.6 x 10(-5) M the atrial rate showed down and the following changes in membrane potentials were observed: (1) a transient increase in the amplitude of the action potential (AAP), in the absence of any change in the magnitude of the resting potential (RP), followed by a progressive decrease of AaP; (2) a progressive decline of the slope of the fast ascending phase of the action potential, which was initially independent of any change in the magnitude of the rp; (3) a progressive increase of the duration of the action potential; (4) a fall in the magnitude of the resting potential. The conclusions proposed are that harmaline: (1) stimulates the slow current responsible for the last part of the upstroke and the beginning of the repolarization; (2) inhibits the sodium current responsible for the fast component of the upstroke; (3) slows doen the processes responsible for the repolarization; (4) inhibits the (Na+-K+) activated membrane ATPase.
Insights
Harmaline affects rat atrial electrophysiology by slowing heart rate and altering action potentials. It impacts ion currents and ATPase activity, influencing cardiac function.
Area of Science:
- Cardiology
- Pharmacology
- Electrophysiology
Background:
- Cardiac electrophysiology is crucial for heart function.
- Understanding drug effects on ion channels is vital for cardiovascular research.
Purpose of the Study:
- To investigate the electrophysiological effects of harmaline on rat atria.
- To elucidate the mechanisms by which harmaline influences cardiac action potentials.
Main Methods:
- In vitro perfusion of rat atria at 30°C.
- Electrical stimulation and spontaneous beating preparations.
- Measurement of membrane potentials and action potential parameters.
Main Results:
- Harmaline (8.3-16.6 x 10(-5) M) decreased atrial rate.
- Observed transient increase and subsequent decrease in action potential amplitude.
- Progressive decline in the upstroke's fast phase slope.
- Increased action potential duration and decreased resting potential.
Conclusions:
- Harmaline stimulates the slow inward current.
- Harmaline inhibits the fast sodium current.
- Harmaline slows repolarization processes.
- Harmaline inhibits Na+-K+ ATPase activity.