Antigen-specific effects of autoantibodies against sarcolemmal Na–K-ATPase pump in immunized cardiomyopathic rabbits

Objectives We examine antigen-specific actions of autoantibodies directed against sarcolemmal Na–K-ATPase. Background Autoantibodies against some receptors or pumps were detected in patients with dilated cardiomyopathy. Although immunoglobulin adsorption therapy improved cardiac function in such patients, direct pathogenic effects of autoantibodies remain to be proven. Methods Japanese white rabbits were immunized once a month with purified Na–K-ATPase (NKA rabbits, n = 10) or a synthetic peptide corresponding to the second extracellular loop of beta1-adrenergic receptors (beta rabbits, n = 10), respectively. Control rabbits (n = 10) received vehicle in the same manner. Results At 6 months, cardiac hypertrophy along with increased left ventricular end-diastolic pressure was observed in both NKA and beta rabbits, and inhibitory G protein level increased in both NKA and beta rabbits. Histological findings showed similar myocyte hypertrophy and interstitial fibrosis in both rabbits. Enzymatic activities of Na–K-ATPase were lower in NKA rabbits than in other groups. Immunoblotting showed that alpha3-isoform of Na–K-ATPase was selectively reduced in myocardium from NKA rabbits. Conclusions Our present findings suggested that isoform-specific alterations of myocardial Na–K-ATPase activity were induced by immunizing rabbits. This was not secondary change due to cardiac hypertrophy. Thus, autoantibodies against sarcolemmal Na–K-ATPase have antigen-specific effect on the heart in vivo.