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Abnormal intracellular [Ca.sup.2+] cycling plays an important role in cardiac dysfunction and ventricular arrhythmias in the setting of heart failure and transient cardiac ischemia followed by reperfusion (I/R). We hypothesized that overexpression of the sarcoplasmic reticulum [Ca.sup.2+] ATPase pump (SERCA2a) may improve both contractile dysfunction and ventricular arrhythmias. Continuous ECG recordings were obtained in 46 conscious rats after adenoviral gene transfer of either SERCA2a or the reporter gene [bets]-galactosidase ([beta]gal) or parvalbumin (PV), as early as 48 h before and 48 h after 30 min ligation of the left anterior descending artery by using an implantable telemetry system. Sham-operated animals were used for comparison for hemodynamic measurements, whereas within-animal baseline was used for electrocardiographic and echocardiographic parameters. All episodes of nonsustained ventricular tachycardia (VT) and ventricular fibrillation (VF) were counted, and their durations were summed by telemetry. I/R decreased regional cardiac wall thickening as well as the maximal rate of left ventricular pressure rise (+dP/dt) and ventricular pressure fall (-dP/dt). SERCA2a restored regional wall thickening and +dP/dt and -dP/dt to levels seen preoperatively. Regional-wall motion and anterior-wall thickening were improved in the SERCA2a animals, as assessed by echocardiography and piezoelectric crystals. To assess whether these effects are SERCA2a specific, we overexpressed a skeletal-muscle protein, PV, to examine whether [Ca.sup.2+] buffering alone can mitigate ventricular arrhythmias. During the first hour after I/R, the rate of nonsustained VT plus VF was 16 [+ or -] 5 episodes per h (n = 6) in the Ad.[beta]gal group, 22 [+ or -] 6 in the Ad.PV group, and 4 [+ or -] 2 (n = 6, P < 0.01) in the Ad.SERCA2a group. The decrease in VT plus VF in the Ad.SERCA2a group was consistent throughout the 48 h of monitoring. These results show that improving intracellular [Ca.sup.2+] handling by overexpression of SERCA2a restores contractile function and reduces ventricular arrhythmias during I/R.

We used a catheter-based technique to achieve generalized cardiac gene transfer in vivo and to alter cardiac function by overexpressing phospholamban (PL) which regulates the activity of the sarcoplasmic reticulum [Ca.sup.2+] ATPase (SERCA2a). By using this approach, rat hearts were transduced in vivo with 5 x [10.sup.9] pfu of recombinant adenoviral vectors carrying cDNA for either PL, [Beta]-galactosidase ([Beta]-gal), or modified green fluorescent protein (EGFP). Western blot analysis of ventricles obtained from rats transduced by Ad.PL showed a 2.8-fold increase in PL compared with hearts transduced by Ad.[Beta]gal. Two days after infection, rat hearts transduced with Ad.PL had lower peak left ventricular pressure (58.3 [+ or -] 12.9 mmHg, n = 8) compared with uninfected hearts (92.5 [+ or -] 3.5 mmHg, n = 6) or hearts infected with Ad.[Beta]gal (92.6 [+ or -] 5.9 mmHg, n = 6). Both peak rate of pressure rise and pressure fall (+3, 210 [+ or -] 298 mmHg/s, -2, 117 [+ or -] 178 mmHg/s, n = 8) were decreased in hearts overexpressing PL compared with uninfected hearts (+5, 225 [+ or -] 136 mmHg/s, -3, 805 [+ or -] 97 mmHg/s, n = 6) or hearts infected with Ad.[Beta]gal (+5, 108 [+ or -] 167 mmHg/s, -3, 765 [+ or -] 121 mmHg/s, n = 6). The time constant of left ventricular relaxation increased significantly in hearts overexpressing PL (33.4 [+ or -] 3.2 ms, n = 8) compared with uninfected hearts (18.5 [+ or -] 1.0 ms, n = 6) or hearts infected with Ad.[Beta]gal (20.8 [+ or -] 2.1 ms, n = 6). These differences in ventricular function were maintained 7 days after infection. These studies open the prospect of using somatic gene transfer to modulate overall cardiac function in vivo for either experimental or therapeutic applications.

In human and experimental models of heart failure, sarcoplasmic reticulum [Ca.sup.2+] ATPase (SERCA2a) activity is decreased, resulting in abnormal calcium handling. The disturbances in calcium metabolism have been shown to contribute significantly to the contractile dysfunction observed in heart failure. We investigated whether increasing SERCA2a expression can improve ventricular function in an animal model of heart failure obtained by creating ascending aortic constriction in rats. After 19-23 wk of banding during the transition from compensated hypertrophy to heart failure (documented by [is greater than] 25% decrease in fractional shortening), rats were randomized to receive either an adenovirus carrying the SERCA2a gene (Ad. SERCA2a, n = 13) or [Beta]-galactosidase (Ad.[Beta]gal, n = 14) by using a catheter-based technique. The failing hearts infected with Ad.[Beta]gal were characterized by a significant decrease in SERCA2a expression and a decrease in SERCA2a activity compared with nonfailing sham-operated rats (n = 11). In addition, these failing hearts had reduced left-ventricular systolic pressure, maximal rate of left-ventricular pressure rise and decline (+dP/dt, -dP/dt), and rate of isovolumic relaxation ([Tau]). Overexpression of SERCA2a restored both SERCA2a expression and ATPase activity to nonfailing levels. Furthermore, rats infected with Ad.SERCA2a had significant improvement in left-ventricular systolic pressure, +dP/dt, -dP/dt, and rate of isovolumic relaxation ([Tau]) normalizing them back to levels comparable to sham-operated rats. In this study, we show that in an animal model of heart failure where SERCA2a protein levels and activity are decreased and severe contractile dysfunction is present, overexpression of SERCA2a in vivo restores both systolic and diastolic function to normal levels.