NHE-1 blockade reversed changes in calcium transient in myocardial slices from isoproterenol-induced hypertrophied rat left ventricle.

We previously reported that left ventricular (LV) slices from isoproterenol (ISO)-induced hypertrophied rat hearts showed an increase of energy expenditure due to remodeling of Ca(2+) handling in excitation-contraction coupling, i.e., suppressed SERCA2a activity and enhanced Na(+)/Ca(2+)exchanger-1 (NCX-1) activity. Na(+)/H(+) exchanger-1 (NHE-1) inhibitor (NHEI) has been demonstrated to exert beneficial effects in the development of cardiac remodeling. We hypothesized that a novel NHE-1 selective inhibitor, BIIB723 prevents remodeling of Ca(2+) handling in LV slices of ISO-induced hypertrophied rat hearts mediated by inhibiting NCX-1 activity. The significant shortening in duration of multi-cellular Ca(2+) transient in ISO group was normalized in ISO+BIIB723 group. The significant increase in amplitude of multi-cellular Ca(2+) waves (CaW) generated at high [Ca(2+)](o) of LV slices in ISO group was also normalized in ISO+BIIB723 group. However, the enhanced NCX-1 activity was not antagonized by BIIB723. We recently reported that ISO-induced down-regulation of a Ca(2+) handling protein, SERCA2a, was normalized by BIIB723. Therefore, it seems likely that BIIB723 normalized shortened multi-cellular Ca(2+) transient duration and increased CaW amplitude in LV slices mediated via normalization of SERCA2a activity. Furthermore, the results presented here suggest the multi-cellular Ca(2+) transient duration and CaW amplitude in LV slices might be better indices reflecting SERCA2a activity than SERCA2a protein expression level.

NHE-1 participates in isoproterenol-induced downregulation of SERCA2a and development of cardiac remodeling in rat hearts.

Impaired Ca(2+) handling is one of the main characteristics in heart failure patients. Recently, we reported abnormal expressions of Ca(2+)-handling proteins in isoproterenol (ISO)-induced hypertrophied rat hearts. On the other hand, Na(+)/H(+) exchanger (NHE)-1 inhibitor has been demonstrated to exert beneficial effects in ischemic-reperfusion injury and in the development of cardiac remodeling. The aims of the present study are to investigate the role of NHE-1 on Ca(2+) handling and development of cardiac hypertrophy in ISO-infused rats. Male Wistar rats were randomly divided into vehicle [control (CTL)] and ISO groups without or with pretreatment with a selective NHE-1 inhibitor, BIIB-723. ISO infusion for 1 wk significantly increased the ratios of heart to body weight and left ventricle (LV) to body weight and collagen accumulation. All of these increases were antagonized by coadministration with BIIB-723. The ISO-induced significant increase in LV wall thickness was suppressed significantly (P < 0.05) by BIIB-723. ISO-induced decreases in cardiac stroke volume and a total mechanical energy per beat index, systolic pressure-volume area at midrange LV volume, were normalized by BIIB-723. The markedly higher expression of NHE-1 protein in the ISO group than that in CTL group was suppressed (P < 0.05) by BIIB-723. Surprisingly, ISO induced downregulation of the important Ca(2+)-handling protein sarcoplasmic reticulum Ca(2+)-ATPase 2a, the expression of which was also normalized by BIIB-723 without changes in phosphorylated phospholamban (PLB)/PLB expression. We conclude that NHE-1 contributes to ISO-induced abnormal Ca(2+) handling associated with cardiac hypertrophy. Inhibition of NHE-1 ameliorates cardiac Ca(2+)-handling impairment and prevents the development of cardiac dysfunction in ISO-infused rats.

Inverse relationship between serum erythropoietin and blood lead concentrations in Kathmandu tricycle taxi drivers.

OBJECTIVE: Kathmandu tricycle taxi drivers, whose environmental lead (Pb) exposure is ascribable mainly to vehicular exhaust, were studied to examine a dose-response relationship between blood Pb (Pb-B) and serum erythropoietin (sEPO) concentrations. METHODS: Subjects were 27 drivers and 9 non-drivers. They were non-anemic healthy men with normal renal function. Pb-B was measured by an atomic absorption spectrometer with a graphite furnace, and sEPO was determined with a sandwich-type enzyme-linked immunosorbent assay. RESULTS: sEPO levels in drivers were lower than those of non-drivers, while Pb-B levels in drivers were higher than those of non-drivers. There was an inverse relationship between Pb-B and sEPO. CONCLUSIONS: The data suggest that Pb inhibits renal EPO production in a dose-dependent manner in persons with subclinical Pb toxicity. sEPO may serve as an early biochemical marker of subclinical Pb toxicity.