Abstract 18739: Acute Effect of the Na+/ca2+ Exchanger (ncx) Inhibitor Sea0400 on Diastolic Function in vivo and in vitro in a Model of Heart Failure With Preserved Ejection Fraction

Abstract

Background: Heart failure with preserved ejection fraction (HFPEF) is increasingly common but underlying cellular mechanisms are not well understood. We investigated cardiomyocyte function and the role of SEA0400, in vivo and in vitro in a rat model of diastolic heart failure. Methods: Young male Wistar rats were subjected to subtotal nephrectomy (NXT) or sham operation (SOP). After 24 weeks in vivo (pressure-volume loops) and in vitro characterization (cardiomyocyte function (Ca2+ transients, sarcoplasmic reticulum (SR) diastolic Ca2+ leak (Ca2+ sparks) and SR Ca2+ content)) as well as NCX function (caffeine-induced Ca2+ transient, TAU) and protein expression) were determined without an with the NCX inhibitor SEA0400 (in vivo: 1 mg/kgKG for 30 minutes/ in vitro: 300nM for 5 minutes incubation). Results: NXT rats showed stable compensated renal impairment and signs and symptoms of HFPEF (hypertrophied left ventricle (LV), left- and upward shift of end diastolic pressure (EDP) volume relationship, increased lung weight/body weight ratio indicating pulmonary congestion and preserved LV systolic function (EF, dP/dt)). In LV cardiomyocytes from NXT Ca2+ transient amplitude was unchanged but time for early (50%) decay was significantly prolonged at 24 weeks and correlated with diastolic dysfunction (EDP) in vivo. TAU of the caffeine transient was significantly prolonged at 24 weeks indicating reduced NCX forward mode activity, while NCX protein expression was up-regulated, suggesting increased NCX reverse mode activity. Ca2+ spark frequency was increased and SR Ca2+ content was decreased in NXT (p<0.05). SEA0400 significantly accelerated Ca2+ transient decay and reduced Ca2+ spark frequency in NXT. Acute in vivo treatment with SEA0400 significantly enhanced active relaxation (isovolumetric relaxation constant) of the LV in NXT. Conclusion: This model of HFPEF is associated with prolonged cytosolic Ca2+ decay and increased diastolic Ca2+ leak in LV cardiomyocytes. Acute treatment with NCX inhibitor SEA0400 normalized cytosolic Ca2+ transients, improved net transsarcolemmal Ca2+ export and decreased SR Ca2+ leak in NXT, in line with a role for reverse mode NCX activity in HFPEF. In vivo active relaxation was improved after acute SEA0400 treatment.