Chronic inhibition of Na/H-exchanger attenuates cardiac hypertrophy and prevents cellular remodeling in heart failure

OBJECTIVE: In patients with heart disease, the transition from compensatory hypertrophy to heart failure (HF) is associated with altered calcium handling. Up-regulated Na(+)/H(+)-exchanger (NHE-1) activity underlies increased [Na(+)](i) and disturbance of cellular calcium handling in HF. We hypothesize that chronic inhibition of NHE-1 activity prevents the hypertrophic response, cellular remodeling, and development of HF. METHODS: Rabbits received a control or cariporide (inhibitor of NHE-1) diet for 3 months, starting after induction of combined volume and pressure overload. Age-matched animals served as control. Development of HF was examined echocardiographically and electrocardiographically after 3 months. [Na(+)](i), [Ca(2+)](i), pH(i), and action potentials were measured in left ventricular midmural myocytes with SBFI, indo-1, SNARF, and di-4-anepps. Sarcoplasmic reticulum calcium content was calculated from the response of [Ca(2+)](i) to rapid cooling. Calcium after-transients were elicited by cessation of rapid stimulation (3 Hz) in the presence of 100 nmol/l noradrenalin. RESULTS: Chronic treatment of rabbits with the specific Na(+)/H(+)-exchanger activity inhibitor cariporide greatly attenuated development of hypertrophy and entirely abolished development of HF; the heart/body weight ratio increased only little, no change in lung weight occurred, left ventricular dimensions and fractional shortening changed mildly, ascites was not present, QT duration did not increase, and sudden death did not occur. Chronic cariporide treatment also prevented cellular electrical and ionic remodeling. Myocyte dimensions were unaltered, action potentials were not prolonged, cytoplasmic sodium and NHE-1 activity did not increase, cytoplasmic and SR calcium handling remained undisturbed, and no increase of the incidence of calcium after-transient dependent delayed after depolarizations (DADs) occurred. CONCLUSION: We conclude that enhanced activity of NHE-1 underlies cardiac cellular electrical and ionic remodeling in experimental heart failure, and that chronic dietary treatment with cariporide attenuates hypertrophy, development of HF, and cellular remodeling.