Impaired contractile performance of cultured rabbit ventricular myocytes after adenoviral gene transfer of Na+-Ca2+ exchanger

Na+-Ca2+ exchanger (NCX) gene expression is increased in the failing human heart. We investigated the hypothesis that upregulation of NCX can induce d epressed contractile performance, Overexpression of NCX was achieved in iso lated rabbit ventricular myocytes through adenoviral gene transfer (Ad-NCX) . After 48 hours, immunoblots revealed a virus dose-dependent increase in N CX protein. Adenoviral beta-galactosidase transfection served as a control. The fractional shortening (FS) of electrically stimulated myocytes was ana lyzed. At 60 min(-1), FS was depressed by 15.6% in the Ad-NCX group (n=143) versus the control group (n=163, P<0.05). Analysis of the shortening-frequ ency relationship showed a steady increase in FS in the control myocytes (n =26) from 0.027+/-0.002 at 30 min(-1) to 0.037+/-0.002 at 120 min(-1) (P<0. 05 versus 30 min(-1)) and to 0.040+/-0.002 at 180 min(-1) (P<0.05 versus 30 min(-1)). Frequency potentiation of shortening was blunted in NCX-transfec ted myocytes (n=27). The FS was 0.024+/-0.002 at 30 min(-1), 0.029+/-0.002 at 120 min(-1) (P<0.05 versus 30 min(-1), P<0.05 versus control), and 0.026 +/-0.002 at 180 min(-1) (NS versus 30 min(-1), P<0.05 versus control). Caff eine contractures, which indicate sarcoplasmic reticulum Ca2+ load, were si gnificantly reduced at 120 min(-1) in NCX-transfected cells. An analysis of postrest behavior showed a decay of FS with longer rest intervals in contr ol cells. Rest decay was significantly higher in the Ad-NCX group; after 12 0 seconds of rest, FS was 78+/-4% in control and 65+/-3% in the Ad-NCX grou p (P<0.05) relative to steady-state FS before rest (100%). In conclusion, t he overexpression of NCX in rabbit cardiomyocytes results in the depression of contractile function. This supports the hypothesis that upregulation of NCX can result in systolic myocardial failure.