Activation of Ca2+/Mg2+ ATPase in heart sarcolemma upon electrical stimulation |
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Authors: | Attila Ziegelhoffer Naranjan S. Dhalla |
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Affiliation: | (1) Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, R3E 0W3 Winnipeg, Canada;(2) Department of Physiology, Faculty of Medicine, University of Manitoba, R3E 0W3 Winnipeg, Canada;(3) Present address: Department of Biochemistry, Institute of Experimental Surgery, Slovak Academy of Sciences, Bratislava, Czechoslovakia |
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Abstract: | Electrical stimulation of the rat heart sarcolemmal membranes with a square wave current was found to increase Ca2+-ATPase activity. This activation of the enzyme was dependent upon the voltage of the electric current, frequency of stimulation and duration of stimulation of the sarcolemmal membranes. The increase in ca2+-ATPase was reversible upon terminating the electrical stimulation. The activation of sarcolemmal Ca2+-ATPase due to electrical stimulation was markedly depressed when the reaction was carried out at high pH (7.8 to 8.2), low pH (6.6 to 7.0), high temperatures (45 to 50°C) and low temperatures (17 to 25°C) of the incubation medium. Ca2+-antagonists, verapamil and D-600, unlike other types of inhibitors such as propranolol and ouabain, were found to reduce the activation of sarcolemmal Ca2+-ATPase by electrical stimulation. These results support the view that Ca2+/Mg2+ ATPase may be involved in the gating mechanism for opening Ca2+-channels in the sarcolemmal membrane upon excitation of the cardiac muscle. |
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Keywords: | cardiac membrane sarcolemmal Ca2+-ATPase verapamil Ca2+ gating mechanism Ca2+ entry into myocardium |
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