SERCA2a overexpression decreases the incidence of aftercontractions in adult rabbit ventricular myocytes

Slow relaxation and poor contractile response to increasing stimulation fre quency in failing human heart have been strongly linked to a decrease in th e activity of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a). Restor ation of SERCA2a levels using gene transfer has beneficial effects on contr actile function but, like beta -adrenoceptor stimulation. could potentially produce excess SR Ca2-. arrhythmias and cell death, We have examined the e ffects of SERCA2a overexpression in adult rabbit cardiac myocytes. and comp ared changes in relaxation with those following beta -adrenoceptor stimulat ion. Myocytes were infected with an adenovirus carrying both SERCA2a and gr een fluorescent protein (GFP) for positive identification of infected cells . Myocyte survival was significantly enhanced in the infected cultures, The re was a reduction in both time-to-peak contraction and time-to-50%, relaxa tion (R50) 48 h after infection. Time-to-90%, relaxation (R90) was particul arly improved (noninfected 516 +/- 41 ms. AD.SERCA2a-GFP 230 +/- 23 ms, n = 7 preparations P < 0.001). There was also a decreased incidence of afterco ntractions in Ad.SERCA2a-GFP infected myocytes (21 +/- 5% v 41 +/- 4% in co ntrols. P < 0.01). This contrasts with beta -adrenoceptor stimulation, whic h reduced R50 but prolonged R90 by 158 +/- 76 ms (P < 0.02. n = 16). At hig her stimulation frequencies (2-3 Hz) contraction amplitude and SR calcium c ontent were increased and diastolic contracture was reduced following SERCA 2a overexpression. Overall, increasing levels of SERCA2a resulted in an imp rovement in systolic and diastolic function and a reduction in cell death a nd arrhythmic aftercontractions. SERCA2a overexpression therefore lacks the detrimental effects associated with some other inotropic interventions. (C ) 2001 Academic Press.