EFFECTS OF ACIDOSIS ON THE EXCITATION-CONTRACTION COUPLING SYSTEM OF CARDIAC MUSCLE
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概要
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The effect of pH 6.4-7.0, a pH known to exist in the ischemic myocardium, was studied on the isolated cardiac sarcoplasmic reticulum (SR) and myofibrils. Oxalate supported SR calcium uptake velocity decreased from 11.0 ± 0.3 × 10^<-3> μmoles Ca^<2+>/mg・min at pH 7.0 in the whole heart homogenate to 4.4 ± 0.2 × 10^<-3> μmoles Ca^<2+>/mg・min at pH 6.4 (p < 0.05). Isolated SR calcium uptake velocity decreased from 0.94 ± 0.01 μmoles Ca^<2+>/mg・min at pH 7.0 to 0.535 ± 0.015 μmoles Ca^<2+>/mg・min at pH 6.4 (p < 0.05) while Ca^<2+>-stimulated. Mg^<2+>-dependent ATPase activity was unaffected by pH (pH 7.0: 1.10 ± 0.05, pH 6.4: 1.10 ± 0.025 μmoles Pi/mg・min). Efficiency ratio of calcium transport, or the coupling ratio, (μmoles Ca^<2+> transported/μmole ATP hydrolyzed) decreased from 0.87 ± 0.064 at pH 7.0 to 0.507 ± 0.05 at pH 6.4 (p < 0.01). Myofibrillar pCa (-log [free Ca^<2+>] ) ATPase activity was unaffected between pH 6.8 and 7.2. At pH 6.6, increasing calcium concentration (pCa < 6.5) inhibited myofibrillar ATPase activity (50% activation at pH 7.0: 6.6, pH 6.6 : 6.3) and this inhibitory phenomenon was accentuated at pH 6.4. It is concluded that pH 6.4-6.6 significantly uncouples calcium transport from ATP hydrolysis in cardiac SR and significantly alters myofibrillar ATPase activity. Comparing these observations with reported pH changes in the ischemic myocardium, it is postulated that increasing proton concentrations can serve as a mediator of contracture in the ischemic myocardium.
- 社団法人日本循環器学会の論文
- 1981-11-20
著者
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Okabe Eiichiro
Department Of Pharmacology Kanagawa Dental College
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Okabe Eiichiro
Deparment Of Pharmacology Kanagawa Dental College
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HESS MICHAEL
The Department of Medicine (Cardiology), Medical College of Virginia
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Hess Michael
The Department Of Medicine (cardiology) Medical College Of Virginia
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