Key result
RV M cells show larger ITO1 and IKs currents and shorter action potential durations than LV.
Why the study?
Although differences in repolarizing K+ currents explain action potential heterogeneity across the LV free wall, the ionic basis of electrical nonuniformity between the RV and LV was poorly investigated.
Differences in repolarizing K+ currents, specifically larger ITO1 and IKs in the right ventricle, explain the interventricular heterogeneity of action potentials in midmyocardial layers of the canine heart.
Answers are grounded in this paper and cite their sources.
Extends LV repolarization heterogeneity to RV-LV differences in canine M cells; hypothesis-generating for human arrhythmia mechanisms.
BACKGROUND: The ventricular action potential exhibits regional heterogeneity in configuration and duration (APD). Across the left ventricular (LV) free wall, this is explained by differences in repolarizing K+ currents. However, the ionic basis of electrical nonuniformity in the right ventricle (RV) versus the LV is poorly investigated. We examined transient outward (ITO1), delayed (IKs and IKr), and inward rectifier K+ currents (IK1) in relation to action potential characteristics of RV and LV midmyocardial (M) cells of the same adult canine hearts. METHODS AND RESULTS: Single RV and LV M cells were used for microelectrode recordings and whole-cell voltage clamping. Action potentials showed deeper notches, shorter APDs at 50% and 95% of repolarization, and less prolongation on slowing of the pacing rate in RV than LV. ITO1 density was significantly larger in RV than LV, whereas steady-state inactivation and rate of recovery were similar. IKs tail currents, measured at -25 mV and insensitive to almokalant (2 micromol/L), were considerably larger in RV than LV. IKr, measured as almokalant-sensitive tail currents at -50 mV, and IK1 were not different in the 2 ventricles. CONCLUSIONS: Differences in K+ currents may well explain the interventricular heterogeneity of action potentials in M layers of the canine heart. These results contribute to a further phenotyping of the ventricular action potential under physiological conditions.
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Volders et al. (1999) studied Normal adult canine ventricular midmyocardium. Right ventricular midmyocardial cells vs. Left ventricular midmyocardial cells was evaluated on Action potential characteristics and repolarizing K+ currents (ITO1, IKs, IKr, and IK1). Right ventricular midmyocardial cells had larger ITO1 and IKs currents and shorter action potential durations at 50% and 95% repolarization than left ventricular M cells.
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