Transient outward current prominent in canine ventricular epicardium but not endocardium.
Key result
A transient outward current (Ito) with slow (tau 350-570 msec) and fast (tau 41-85 msec) components significantly contributes to canine ventricular epicardial, but not endocardial, action potentials.
Population
Canine ventricular myocardium (epicardium and endocardium)
Comparison
Electrophysiological evaluation with 1-5 mM… vs Endocardium vs Epicardium; baseline vs…
Design
Preclinical
Authors
Discussion
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Implication
Ito heterogeneity in canine ventricle warrants human studies; leaves open its role in clinical repolarization or arrhythmias.
Key Points
- To determine whether a transient outward current contributes to action potential differences between the epicardial and endocardial layers of canine ventricular myocardium.
- Recorded action potentials from canine ventricular epicardium and endocardium using conventional microelectrode techniques across varying stimulation rates.
- Characterized phase 1 restitution kinetics and evaluated the effects of 4-aminopyridine (1–5 mM), ryanodine, and replacement of Ca2+ with Sr2+.
- Epicardial action potentials exhibited a distinct 'spike and dome' morphology with a prominent phase 1 that became accentuated at slower rates, which was absent in endocardium.
- Phase 1 restitution identified a slow recovery component (time constant: 350–570 ms) sensitive to 4-aminopyridine and a fast component (time constant: 41–85 ms) sensitive to 4-aminopyridine, ryanodine, and Sr2+.
- Pharmacological inhibition of the transient outward current transformed the epicardial action potential configuration to resemble that of endocardium.
Structured PICO
P
Population
Canine ventricular myocardium (epicardium and endocardium)
I
Intervention
Electrophysiological evaluation with 1-5 mM 4-aminopyridine, ryanodine, and Sr2+ replacement of Ca2+
C
Comparator
Endocardium vs Epicardium; baseline vs post-intervention
O
Outcome
Action potential morphology and restitution of phase 1 amplitudesurrogate
Demonstrates the presence of a transient outward current (Ito) in canine ventricular epicardium but not endocardium, explaining the 'spike and dome' action potential morphology.
Cite This Study
Litovsky et al. (1988) studied Canine ventricular electrophysiology. 4-aminopyridine, ryanodine, and Sr2+ vs. Endocardium was evaluated on Action potential phase 1 amplitude restitution. A transient outward current (Ito) with slow (tau 350-570 msec) and fast (tau 41-85 msec) components significantly contributes to canine ventricular epicardial, but not endocardial, action potentials.