Verapamil이 心筋 小胞體의 Mg^++-Ca^++-ATPase 活性에 미치는 影響 = Effects of Verapamil on the Mg^++-Ca^++-ATPase Activity of Cardiac Sarcoplasmic Recticulum

다국어 초록 (Multilingual Abstract)

The present experiments were designed to investigate the effect of verapamil on the Mg^++-Ca^++-ATPase activity. The inhibitory effect of cardiac muscle contractility was measured by physiograph, and the effect of the drug on the Mg^++-Ca^++-ATPase activity was analyzed by enzyme kinetics such as Dixon plot and Lineweaver-Burk plot. The results obtained here were as follows :
1. The contractility of the ventricular muscle was decreased to 74 % after 20min, infusion in the presence of verpamil(0.01mM). Though EDTA was also added to the infusion buffer, the inhibitory effect of verapamil was not changed.
2. The concentration of 50% inhibition for verapamil coincided with the inhibition constant(Ki). The Ki value was 0.01 for verapamil.
3. Verapamil did not change the Km value(5), but decrease V_max of the enzyme activity; suggesting that verapamil acts as a reversible and noncompetitive inhibitor.
From the above results, verapamil inhibits the Mg^++-Ca^++-ATPase Activity as an noncompetitive inhibitor, and thus Ca^++ could not be released from cardiac sarcoplasmic reticulum.