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Rate dependency of delayed rectifier currents during the guinea-pig ventricular action potential
M Rocchetti1, A Besana, G B Gurrola
1Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy.
The Journal of Physiology
|August 3, 2001
Summary
The study reveals that both rapid delayed rectifier potassium currents (I(Kr)) and slow (I(Ks)) increase with faster heart rates through distinct mechanisms. This rate dependency is crucial for understanding repolarization abnormalities in heart conditions.
Area of Science:
- Cardiovascular Physiology
- Electrophysiology
- Molecular Cardiology
Background:
- The rate dependency of cardiac ion channels is critical for normal heart function.
- Delayed rectifier potassium currents, specifically I(Kr) and I(Ks), play key roles in cardiac repolarization.
- Understanding their behavior at physiological heart rates is essential for diagnosing and treating cardiac arrhythmias.
Purpose of the Study:
- To investigate the rate-dependent characteristics of I(Kr) and I(Ks) under physiological pacing conditions.
- To elucidate the specific contributions of action potential shape and diastolic interval to the modulation of these currents.
- To determine the relationship between repolarization rate and I(Kr) behavior, and its impact on action potential duration.
Main Methods:
- Utilized the action potential clamp technique in guinea-pig ventricular myocytes.
- Measured I(Kr) and I(Ks) at different pacing cycle lengths (1000 ms and 250 ms).
- Employed ramp clamp and constant current injection (I-clamp) to assess repolarization dynamics and current block effects.
Main Results:
- Shorter pacing cycle lengths led to earlier activation and increased magnitude of both I(Kr) and I(Ks).
- Shortening diastolic interval enhanced I(Ks), while altered action potential shape primarily affected I(Kr).
- I(Kr) amplitude showed a complex, non-linear relationship with repolarization rate, and its block effect on action potential duration was reduced at high repolarization rates.
Conclusions:
- Both I(Kr) and I(Ks) exhibit rate-dependent increases at faster heart rates, mediated by distinct electrophysiological mechanisms.
- These identified mechanisms contribute to abnormal repolarization rate dependency observed in prolonged repolarization syndromes.
- The complex behavior of I(Kr) was accurately modeled using known kinetic properties, validating experimental findings.