A cardioprotective agent of a novel calpain inhibitor, SNJ-1945, exerts β1 actions on left ventricular mechanical work and energetics

Abstract

We have previously shown that a newly developed calpain inhibitor, SNJ-1945 (SNJ), with good aqueous solubility prevents the heart from KCl arrest-reperfusion injury associated with the impairment of total Ca2+ handling by inhibiting the proteolysis of α-fodrin as a cardioplegia. The aim of the present study was to investigate certain actions of this calpain inhibitor, SNJ, on left ventricular (LV) mechanical work and energetics in cross-circulated excised rat hearts undergoing blood perfusion with 40 μM SNJ. Mean end-systolic pressure at midrange LV volume and systolic pressure-volume area (PVA) at mLVV (a total mechanical energy/beat) were significantly increased by SNJ perfusion ( P < 0.01). Mean myocardial oxygen consumption per beat (V̇o2) intercepts (V̇o2 for the total Ca2+ handling in excitation-contraction coupling and basal metabolism) of V̇o2-PVA linear relations were significantly increased ( P < 0.01) with unchanged mean slopes of V̇o2-PVA linear relations. Pretreatment with the selective β1-blocker landiolol (10 μM) blocked these effects of SNJ perfusion. There were no significant differences in mean basal metabolic oxygen consumption among normal, 40 μM SNJ, and 10 μM landiolol + 40 μM SNJ groups. Our results indicate that water-soluble SNJ exerted positive actions on mechanical work and energetics mediated via β1-adrenergic receptors associated with the enhancement of total Ca2+ handling in excitation-contraction coupling and with unchanged contractile efficiency. In clinical settings, this pharmacological action of SNJ is beneficial as an additive agent for cardioplegia.