title: Sex-based transmural differences in cardiac repolarization and ionic-current properties in canine left ventricles.
abstract: The female sex is associated with longer electrocardiographic QT intervals and increased proarrhythmic risks of QT-prolonging drugs. This study examined the hypothesis that sex differences in repolarization may be associated with differential transmural ion-current distribution. Whole cell patch-clamp and current-clamp were used to study ionic currents and action potentials (APs) in isolated canine left ventricular cells from epicardium, midmyocardium, and endocardium. No sex differences in AP duration (APD) were found in cells from epicardium versus endocardium. In midmyocardium, APD was significantly longer in female dogs (e.g., at 1 Hz, female vs. male: 288 +/- 21 vs. 237 +/- 8 ms; P < 0.05), resulting in greater transmural APD heterogeneity in females. No sex differences in inward rectifier K+ current (I(K1)) were observed. Transient outward K+ current (I(to)) densities in epicardium and midmyocardium also showed no sex differences. In endocardium, female dogs had significantly smaller I(to) (e.g., at +30 mV, female vs. male: 2.5 +/- 0.2 vs. 3.5 +/- 0.3 pA/pF; P < 0.05). Rapid delayed-rectifier K+ current (I(Kr)) density and activation voltage-dependence showed no sex differences. Female dogs had significantly larger slow delayed-rectifier K+ current (I(Ks)) in epicardium and endocardium (e.g., at +40 mV; tail densities, female vs. male; epicardium: 1.3 +/- 0.1 vs. 0.8 +/- 0.1 pA/pF; P < 0.001; endocardium: 1.2 +/- 0.1 vs. 0.7 +/- 0.1 pA/pF; P < 0.05), but there were no sex differences in midmyocardial I(Ks). Female dogs had larger L-type Ca2+ current (I(Ca,L)) densities in all layers than male dogs (e.g., at -20 mV, female vs. male, epicardium: -4.2 +/- 0.4 vs. -3.2 +/- 0.2 pA/pF; midmyocardium: -4.5 +/- 0.5 vs. -3.3 +/- 0.3 pA/pF; endocarium: -4.5 +/- 0.4 vs. -3.2 +/- 0.3 pA/pF; P < 0.05 for each). We conclude that there are sex-based transmural differences in ionic currents that may underlie sex differences in transmural cardiac repolarization.
authors.affiliation: Department of Pharmacology and Therapeutics, Montreal Heart Institute and University of Montreal, Montreal, Quebec, Canada.
authors.forename: Ling
authors.initials: L
authors.lastname: Xiao
authors.forename: Liming
authors.initials: L
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Han
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wang
authors.forename: Stanley
authors.initials: S
authors.lastname: Nattel
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism / Q000502:physiology; D003627:Data Interpretation, Statistical; D004285:Dogs; D004594:Electrophysiology; D005260:Female; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism* / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology; D012727:Sex Characteristics; D016276:Ventricular Function
chemical_list: D020746:Calcium Channels, L-Type; D007473:Ion Channels; D015221:Potassium Channels