Gender-related differences in ion-channel and transporter subunit expression in non-diseased human hearts

Gender-related differences in ventricular electrophysiology are known to be important determinants of human arrhythmic risk, but the underlying molecular basis is poorly understood. The present work aims to provide the first detailed analysis of gender-related cardiac ion-channel gene-distribution, based on samples from non-diseased human hearts. By using a high-throughput quantitative approach, we investigated at a genome-scale the expression of 79 genes encoding ion-channel and transporter subunits in epicardial and endocardial tissue samples from non-diseased transplant donors (10 males, 10 females). Gender-related expression differences involved key genes implicated in conduction and repolarization. Female hearts showed reduced expression for a variety of K(+)-channel subunits with potentially important roles in cardiac repolarization, including HERG, minK, Kir2.3, Kv1.4, KChIP2, SUR2 and Kir6.2, as well as lower expression of connexin43 and phospholamban. In addition, they demonstrated an isoform switch in Na(+)/K(+)-ATPase, expressing more of the alpha1 and less of the alpha3 subunit than male hearts, along with increased expression of calmodulin-3. Iroquois transcription factors (IRX3, IRX5) were more strongly expressed in female than male epicardium, but the transmural gradient remained. Protein-expression paralleled transcript patterns for all subunits examined: HERG, minK, Kv1.4, KChIP2, IRX5, Nav1.5 and connexin43. Our results indicate that male and female human hearts have significant differences in ion-channel subunit composition, with female hearts showing decreased expression for a number of repolarizing ion-channels. These findings are important for understanding sex-related differences in the susceptibility to ventricular arrhythmias, particularly for conditions associated with repolarization abnormalities like Brugada and Long QT syndrome.