Powers F M, Solaro R J
Department of Physiology and Biophysics, University of Illinois at Chicago 60618.
Am J Physiol. 1995 Jun;268(6 Pt 1):C1348-53. doi: 10.1152/ajpcell.1995.268.6.C1348.
We investigated the mechanism by which caffeine influences myofilament responsiveness to Ca2+ by measuring isometric force, Ca2+ binding, and ATPase activity of dog cardiac myofilament proteins. Caffeine (20 mM) increased submaximal and depressed maximal force in skinned fiber bundles. Although the Ca2+ sensitivity of myofilament activity was increased by caffeine, there was no effect on Ca2+ binding to troponin C (TnC) in skinned fiber bundles. To determine if caffeine altered actin-myosin interaction or affected myosin directly, myofibrillar, actomyosin, and myosin ATPase activities were measured. Maximal Ca(2+)-activated myofibrillar Mg(2+)-ATPase activity was depressed by 20 mM caffeine, whereas submaximal Mg(2+)-ATPase activities were not changed. Actomyosin Mg(2+)-ATPase activity was significantly depressed by caffeine concentrations > or = 15 mM. Myosin Ca(2+)-ATPase activity was depressed by caffeine, whereas Mg(2+)-ATPase and K(EDTA)-ATPase activities were not affected. These data suggest that caffeine affects myofilament function via a mechanism that is independent of TnC-Ca2+ binding but that may involve direct effects on actin-cross-bridge interaction.
我们通过测量犬心肌肌丝蛋白的等长力、钙离子结合及ATP酶活性，研究了咖啡因影响肌丝对钙离子反应性的机制。咖啡因（20 mM）可增加去表皮纤维束的次最大力并降低最大力。尽管咖啡因增加了肌丝活性对钙离子的敏感性，但对去表皮纤维束中肌钙蛋白C（TnC）与钙离子的结合没有影响。为确定咖啡因是否改变肌动蛋白-肌球蛋白相互作用或直接影响肌球蛋白，我们测量了肌原纤维、肌动球蛋白和肌球蛋白ATP酶活性。20 mM咖啡因可降低最大钙离子激活的肌原纤维镁离子-ATP酶活性，而次最大镁离子-ATP酶活性未改变。咖啡因浓度≥15 mM时，肌动球蛋白镁离子-ATP酶活性显著降低。咖啡因可降低肌球蛋白钙离子-ATP酶活性，而镁离子-ATP酶和乙二胺四乙酸钾-ATP酶活性不受影响。这些数据表明，咖啡因通过一种独立于TnC-钙离子结合的机制影响肌丝功能，但可能涉及对肌动蛋白横桥相互作用的直接影响。
