Upregulation of SERCA2a following short-term ACE inhibition (by enalaprilat) alters contractile performance and arrhythmogenicity of healthy myocardium in rat.

Chronic angiotensin-converting enzyme inhibitor (ACEIs) treatment can suppress arrhythmogenesis. To examine whether the effect is more immediate and independent of suppression of pathological remodelling, we tested the antiarrhythmic effect of short-term ACE inhibition in healthy normotensive rats. Wistar rats were administered with enalaprilat (ENA, i.p., 5 mg/kg every 12 h) or vehicle (CON) for 2 weeks. Intraarterial blood pressure in situ was measured in A. carotis. Cellular shortening was measured in isolated, electrically paced cardiomyocytes. Standard 12-lead electrocardiography was performed, and hearts of anaesthetized open-chest rats were subjected to 6-min ischemia followed by 10-min reperfusion to examine susceptibility to ventricular arrhythmias. Expressions of calcium-regulating proteins (SERCA2a, cardiac sarco/endoplasmic reticulum Ca(2+)-ATPase; CSQ, calsequestrin; TRD, triadin; PLB, phospholamban; Thr(17)-PLB-phosphorylated PLB at threonine-17, FKBP12.6, FK506-binding protein, Cav1.2-voltage-dependent L-type calcium channel alpha 1C subunit) were measured by Western blot; mRNA levels of L-type calcium channel (Cacna1c), ryanodine receptor (Ryr2) and potassium channels Kcnh2 and Kcnq1 were measured by qRT-PCR. ENA decreased intraarterial systolic as well as diastolic blood pressure (by 20%, and by 31%, respectively, for both P < 0.05) but enhanced shortening of cardiomyocytes at basal conditions (by 34%, P < 0.05) and under beta-adrenergic stimulation (by 73%, P < 0.05). Enalaprilat shortened QTc interval duration (CON 78 ± 1 ms vs. ENA 72 ± 2 ms; P < 0.05) and significantly decreased the total duration of ventricular fibrillations (VF) and the number of VF episodes (P < 0.05). Reduction in arrhythmogenesis was associated with a pronounced upregulation of SERCA2a (CON 100 ± 20 vs. ENA 304 ± 13; P < 0.05) and complete absence of basal Ca(2+)/calmodulin-dependent phosphorylation of PLB at Thr(17). Short-term ACEI treatment can provide protection against I/R injury-induced ventricular arrhythmias in healthy myocardium, and this effect is associated with increased SERCA2a expression.