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Thesis
モノクロタリン心不全ラットの心室筋細胞における細胞内Ca調節

小川　晴美
埼玉医科大学　大学院　臨床医学系　循環器内科学専攻
（指導：西村　重敬 教授）

医学博士　甲第1017号　平成18年3月24日 （埼玉医科大学）

Cytosolic Calicum Regulation in Ventricular Myocytes of Rats with Monocrotalin-Induced Heart Failure
Harumi Ogawa (Department of Cardiology Saitama Medical University, Moroyama, Iruma-gun, Saitama 350-0495, Japan)

　Monocrotaline (MCT) has been well known to induce pulmonary hypertension (PH) without changing systemic blood pressure in animal models. We previously reported that pathological hypertrophy occurred in left ventricle (LV) as well as in right ventricle (RV) with MCT-induced PH model although neither pressure or volume overload was burdened on LV. Our purpose is to examine differences in [Ca²⁺]_i regulation between hypertrophic myocytes with pressure overload (RV myocytes) and those without pressure overload (LV myocytes). Our working hypothesis was that RV remodeling due to both direct mechanical overload and neurohumoral factors may have different effects on myocyte Ca²⁺ regulation in comparison with LV remodeling solely due to neurohumoral factors. We injected MCT or control saline intraperitonealy and observed these rats for 6 weeks. We lost some of them due to pump failure or other complications. Ventricular myocytes were isolated enzymatically from RV and LV free walls 6 weeks after injection. We measured [Ca²⁺]_i beat to beat basis using fluo-3 as previously reported. In stabilized electrically-activated [Ca²⁺]_i transients, the peak systolic [Ca²⁺]_i and the amplitude of [Ca²⁺]_i significantly increased in LV myocytes of MCT rats as compared with LV myocytes of Sham rats or RV myocytes of MCT rats. The decline phase of [Ca²⁺]_i transients were also accelerated in LV myocytes of MCT rats. But these parameters were not changed in RV myocytes of MCT rats in comparison with RV myocytes of Sham rats. Protein kinase activation of myocytes increased peak systolic [Ca²⁺]_i but decreased the decline speed of [Ca²⁺]_i transients in both LV and RV of MCT and Sham. The normalized [Ca²⁺]_i transients decline speed was not associated with plasma brain natriuretic peptide level (a well known marker of heart failure grading).
　To examine whether these Ca²⁺ handling changes were due to Ca²⁺ handling gene expression, we performed RNAse protection assay for sarcoplasmic endoplasmic reticulum Ca ATPase (SERCA) and Na-Ca exchanger (NCX). These assays did not show significant changes in the expression of SERCA and NCX genes.
Thus the Ca²⁺a handling was altered in both LV and RV ventricular myocytes from MCT-induced rat hearts. But the data described above strongly suggested that the alterations of Ca²⁺ handling in MCT rat hearts were not due to the changes in SERCA or NCX gene expression but due to the changes in SERCA and/or NCX functions. The mechanisms in alterations of SERCA and NCX function may involve phosphorylation state of these proteins.
Keywords: Monocrotaline, Congestive Heart Failure, Ventricular Remodeling, Calcium Handling, Fluo-3