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Ca-dependent outward currents in bullfrog myocardium
The Japanese Journal of Physiology
|January 1, 1983
Summary
Calcium ions significantly influence outward currents in bullfrog atrial muscle. Researchers identified three distinct calcium-sensitive outward currents, impacting cardiac electrical activity and muscle contraction.
Area of Science:
- Cardiac Electrophysiology
- Ion Channel Physiology
- Cardiovascular Pharmacology
Background:
- Calcium ions (Ca2+) play a crucial role in cardiac muscle function, regulating both excitation-contraction coupling and electrical activity.
- Outward currents are essential for cardiac repolarization and maintaining the cardiac action potential.
- Understanding the specific properties and regulation of Ca2+-dependent currents is vital for comprehending cardiac electrophysiology.
Purpose of the Study:
- To investigate the properties of Ca2+-dependent outward currents in bullfrog atrial muscle.
- To elucidate the relationship between extracellular calcium concentration ([Ca]o) and specific ionic currents.
- To classify the different components of Ca2+-sensitive outward currents.
Main Methods:
- Utilized double sucrose-gap techniques to study ionic currents in bullfrog atrial muscle.
- Manipulated extracellular calcium concentrations ([Ca]o) and employed specific blockers (Ba2+, TTX, Co2+, EGTA) to isolate and characterize currents.
- Investigated the effects of isoproterenol on ionic currents.
Main Results:
- Decreasing [Ca]o inhibited instantaneous outward current (Ik1) and inward background current (Ib); increasing [Ca]o had the opposite effect.
- Barium (Ba2+) blocked Ik1, indicating these effects were Ca2+-dependent.
- Cobalt (Co2+) abolished slow inward current (Isi) and depressed delayed outward current (Iout) in a voltage-dependent manner, while isoproterenol enhanced both currents.
- Ca2+-free conditions further depressed Iout, altering activation and deactivation kinetics.
Conclusions:
- Identified and classified three distinct Ca2+-sensitive outward currents: Ca2+-linked Ik1, Isi-dependent Iout, and Isi-independent but [Ca]o-related Iout.
- Demonstrated the significant role of extracellular calcium in modulating cardiac outward currents and their kinetics.
- Highlighted the differential effects of pharmacological agents (Co2+, isoproterenol) on these currents, providing insights into cardiac electrophysiological regulation.