© 1995 American Heart Association, Inc.
Articles |
MCI-154 Increases Ca2+ Sensitivity of Reconstituted Thin Filament
A Study Using a Novel In Vitro Motility Assay Technique
From the Second Department of Internal Medicine, Faculty of Medicine, University of Tokyo (Japan).
Correspondence to Masataka Sata, MD, Department of Physiology & Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106-4970.
Abstract MCI-154 (6-[4-(4'-pyridylamino)phenyl]-4,5-dihydro-3(2H)pyridazinone hydrochloride trihydrate) is a potent novel cardiotonic agent whose positive inotropism is shown to be mainly based on an increase in Ca2+ sensitivity of the contractile apparatus. To elucidate the exact mechanism through which this drug acts, we investigated the movement of the reconstituted thin filament on a myosin layer in vitro. Cardiac thin filaments were reconstituted from actin and tropomyosin-troponin complex purified from rat cardiac acetone powder separately. Double staining of the filament showed that tropomyosin-troponin complex was integrated along actin filament homogeneously. Thin filaments thus prepared were fluorescently labeled and made to slide on rat cardiac myosin fixed on a glass coverslip while varying the [Ca2+] of the medium (control, pH 7.2 at 25°C). When [Ca2+] was low, the filaments showed only brownian motion. However, above a certain level of [Ca2+] (the threshold [Ca2+]), the filaments started to slide, and the velocity increased, reaching the maximum velocity within a very narrow range of [Ca2+]. The regulation was completely abolished by using simple actin filaments without tropomyosin-troponin complex, demonstrating that the regulatory proteins are responsible for this Ca2+ regulation of the movement of the reconstituted thin filament. Under the control condition, addition of MCI-154 shifted the threshold [Ca2+] to a lower level (sensitization) in a concentration-related manner. And 10-4 mol/L of MCI-154 reversed the desensitization effect induced by either acidosis (pH 6.8), low temperature (15°C), or the addition of inorganic phosphate (10 mmol/L). However, the maximum sliding velocity was not affected by the drug under any condition. In conclusion, MCI-154 directly sensitized the contractile apparatus under not only physiological but also pathophysiological conditions. This in vitro motility assay technique using reconstituted thin filaments is a useful tool for studying the mechanism of action of Ca2+ sensitizers.
Key Words: Ca2+ sensitizer • myosin • regulatory proteins • in vitro motility assay
This article has been cited by other articles:
 |
|
 |
|
  D. A. Kass and R. J. Solaro Mechanisms and Use of Calcium-Sensitizing Agents in the Failing Heart Circulation, January 17, 2006; 113(2): 305 - 315. [Full Text] [PDF]
|
|
|
|
 |
|
 K. Eto, K. Hashimoto, and H. Nakaya Preferential inhibition of IKr by MCI-154, a putative cardiotonic Ca2+ sensitizer, in guinea pig atrial cells Cardiovasc Res, June 1, 1998; 38(3): 685 - 694. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Teramura, T. Yamakado, M. Maeda, and T. Nakano Effects of MCI-154, a Calcium Sensitizer, on Left Ventricular Systolic and Diastolic Function in Pacing-Induced Heart Failure in the Dog Circulation, February 4, 1997; 95(3): 732 - 739. [Abstract] [Full Text]
|
|
|
|
|
|
M. Sata, S. Sugiura, H. Yamashita, S.-i. Momomura, and T. Serizawa Coupling Between Myosin ATPase Cycle and Creatine Kinase Cycle Facilitates Cardiac Actomyosin Sliding In Vitro : A Clue to Mechanical Dysfunction During Myocardial Ischemia Circulation, January 15, 1996; 93(2): 310 - 317. [Abstract] [Full Text]
|
|