The Na +/Ca 2+ Exchanger/SR Ca 2+ ATPase Transport Capacity Regulates the Contractility of Normal and Hypertrophied Feline Ventricular Myocytes

Abstract

Background Pressure overload leads to cardiac hypertrophy, which is often followed by heart failure. We tested the hypothesis that depressed contractility in this process results from an imbalance in Ca 2+ transport by the sarcoplasmic reticulum (SR) Ca 2+ ATPase (SERCA) and the sarcolemmal Na +/Ca 2+ exchanger (NCX). Methods and Results Left ventricular (LV) myocytes (n = 79) from 12 normal (N) and 5 hypertrophied (LVH, by aortic banding) feline hearts were studied. Adenoviral gene transfer was used to introduce green fluorescent protein (GFP), SERCA2, and NCX into N and LVH myocytes. Contraction (videomicroscopy) and Ca 2+ transients (Fluo-3) were measured in steady state and after rest periods of 2 to 120 seconds (rest decay and potentiation). LVH hearts were significantly larger than N (7.1 ± 1.4 versus 4.2 ± 0.2 g/kg). SERCA protein was significantly less abundant in LVH versus N. Steady state contractions and Ca 2+ transients of LVH-GFP myocytes decayed more slowly and rest decay of contractility was more pronounced compared with N-GFP. Infection of LVH (and N) myocytes with SERCA increased basal contractility and reduced rest decay. Infection of LVH myocytes with NCX almost abolished contraction and in N myocytes reduced contractility and increased rest decay. Conclusion These findings suggest that an imbalance of Ca 2+ transport by SERCA and the NCX produces the characteristic contractile abnormalities of hypertrophied cardiac myocytes.