Chronic Exposure to Low Doses of HgCl2 Avoids Calcium Handling Impairment in the Right Ventricle after Myocardial Infarction in Rats

et al. (2014) Chronic Exposure to Low Doses of HgCl2 Avoids Calcium Handling Impairment in the Right Ventricle after Myocardial Infarction in Rats. PLoS ONE 9(4): e95639. doi:10.1371/journal.pone.0095639 Chronic Exposure to Low Doses of HgCl2 Avoids Calcium Handling Impairment in the Right Ventricle after Myocardial Infarction in Rats Thas de Oliveira Faria 0 Gustavo Pinto Costa 0 Camila Cruz Pereira Almenara 0 Jhuli Keli Angeli 0 Dalton Valentim Vassallo 0 Ivanita Stefanon 0 Paula Frizera Vassallo 0 Michael Bader, Max-Delbru ck Center for Molecular Medicine (MDC), Germany 0 1 Departamento de Ciencias Fisiolo gicas, Universidade Federal do Esp rito Santo , Vito ria, Brazil, 2 Escola de Ensino Superior da Santa Casa de Miseric o rdia de Vito ria, EMESCAM, Vito ria , Brazil Right ventricle systolic dysfunction is a major risk factor for death and heart failure after myocardial infarction (MI). Heavy metal exposure has been associated with the development of several cardiovascular diseases, such as MI. The aim of this study was to investigate whether chronic exposure to low doses of mercury chloride (HgCl2) enhances the functional deterioration of right ventricle strips after MI. Male Wistar rats were divided into four groups: Control (vehicle); HgCl2 (exposure during 4 weeks- 1st dose 4.6 mg/kg, subsequent dose 0.07 mg/kg/day, i.m. to cover daily loss); MI surgery induced and HgCl2-MI groups. One week after MI, the morphological and hemodynamic measurements and isometric tension of right ventricle strips were investigated. The chronic HgCl2 exposure did not worsen the injury compared with MI alone in the morphological or hemodynamic parameters evaluated. At basal conditions, despite similar maximum isometric force at L-max, relaxation time was increased in the MI group but unaffected in the HgCl2-MI compared to the Control group. Impairment of the sarcoplasmic reticulum (SR) function and reduction in the sarcolemmal calcium influx were observed in MI group associated with SERCA2a reduction and increased PLB protein expression. Induction of MI in chronic HgCl2 exposed rats did not cause any alteration in the developed force at L-max, lusitropic function or 2dF/dt except for a tendency of a reduction SR function. These findings could be partially explained by the normalization in the sarcolemmal calcium influx and the increase in NCX protein expression observed only in this group. These results suggest that chronic exposure to low doses of HgCl2 prevents the impaired SR function and the reduced sarcolemmal calcium influx observed in MI likely by acting on NCX, PLB and SERCA2a protein expression. - Funding: This study was supported by grants from No. 54685435/2011-FAPES (Fundacao de Amparo a` Pesquisa do Esprito Santo), No. 48511935/2009 PRONEX FAPES/CNPq (FAPES/Conselho Nacional de Desenvolvimento Cientifico e Tecnolo gico) and CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nvel Superior. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Myocardial Infarction (MI) is currently the leading cause of morbidity and mortality worldwide, costing the public health system millions every year [1]. The common causes of MI include hypertension [2], atherosclerosis [3], diabetes [4] and a sedentary lifestyle [5]. It is well known that chronic MI can lead to heart failure (HF) [6,7]. Indeed, after a few hours post-MI, the ischemic process in the myocardium begins to cause deleterious effects on the contractile function of the heart [8]. In addition, in isolated heart models, acute MI impaired both the force development and the contractile index [9]. Furthermore, left myocardial dysfunction is associated with an impairment in calcium handling, suggested by a reduction in SERCA and PLB proteins and a decrease in sodium/ calcium exchanger (NCX) activity [10,11]. Importantly, right ventricle dysfunction has been considered as an independent predictor of mortality and also predicts the development of HF in patients with left ventricle dysfunction [12]. Therefore, it is very important to study the alterations in right ventricular function after acute left ventricle MI to elucidate the mechanisms involved in this process. Currently, heavy metal exposure has also been associated with the development of cardiovascular diseases such as atherosclerosis, hypertension, coronary artery disease and MI [13,14,15,16]. Additionally, acute mercury intoxication can produce pulmonary hypertension [17] and impaired vascular pulmonary function in rats [18,19]. Moreover, chronic low doses of mercury chloride (HgCl2) also have an deleterious effect on coronary artery function by producing an increasing resistance to blood flow that might cause contraction and relaxation impairment under vascular overload conditions [20]. In the isolated, perfused heart, chronic exposure to mercury induces alterations in calcium handling mechanisms, such as a reduction in NCX and SERCA expression and the induction of negative inotropic effect [21]. Furthermore, there was an association between the amount of mercury in hair and the risk of MI in humans [22]. Although there is a possibility that MI could occur in individuals exposed to HgCl2, the underling mechanisms involved in MI and low doses of HgCl2 are still unknown. Thus, the aim of this study was to describe the effects of MI on the contractile function of right ventricle strips after chronic exposure to low doses of HgCl2. Materials and Methods Animals Studies were performed on male Wistar rats (170200 g). All experiments were conducted in compliance with the guidelines for biomedical research as stated by the Brazilian Societies of Experimental Biology and approved by a local ethics committee of the Federal University of Esprito Santo (084/2011 CEUAUFES). All rats had ad libitum access to water and rodent chow. Myocardial infarction induction and experimental groups Initially, rats were divided into two groups: Control (vehicle saline solution, i.m) and those treated with mercury chloride for 4 weeks (1st dose 4.6 mg/kg, subsequent dose 0.07 mg/kg/day, i.m to cover daily loss). As previously described, this treatment led to HgCl2 blood levels of approximately 8 ng/mL [20,21,23]. In the present study this was considered as low dose of HgCl2 instead of a toxic dose because our treatment attained to a blood mercury content of 8 ng/ml, that is close to the levels observed in exposed humans [24,25]. After three weeks, another two groups were included in the study: MI animals in the presence or absence of HgCl2 exposure. MI injury was induced after only three weeks to ensure there was a stable blood level of HgCl2 as describe above [23]. MI was induced as previously reported [26]. Briefly, animals were anesthetized with ketamine (50 mg/kg, i.p) and xylazine (10 mg/kg, i.p). The thorax was opened (...truncated)