Schwinger R H, Brixius K, Bavendiek U, Hoischen S, Müller-Ehmsen J, Bölck B, Erdmann E
Klinik III für Innere Medizin der Universität zu Köln, Germany.
J Pharmacol Exp Ther. 1997 Oct;283(1):286-92.
The present study investigated the functional role of the sarcoplasmic reticulum Ca++-ATPase in contraction and relaxation, intracellular Ca++-transients, as well as on the force-frequency relationship in human myocardium. The Ca++-ATPase activity of membrane vesicles isolated from sarcoplasmic reticulum (SR) obtained from nonfailing donor hearts (n = 7) was measured in the presence of cyclopiazonic acid (CPA, 0-30 microM), a highly specific inhibitor of the Ca++-ATPase of the SR (SERCA). The effects of CPA on parameters of contraction and relaxation, force-frequency relationship and [Ca++]i transients (with fura-2) were studied on isolated left ventricular muscle strips from human nonfailing myocardium. CPA concentration-dependently inhibited SERCA activity of isolated SR vesicles. In the presence of CPA (30 microM) the former positive force-frequency relationship in human left ventricular nonfailing myocardium became negative. Especially at high frequencies of stimulation, CPA decreased developed tension, peak rate of tension rise and systolic fura-2-light emission, whereas time to peak tension, time to peak [Ca++]i, time to 95% relaxation, diastolic tension and diastolic Ca++ levels were increased. Peak rate of tension decay and time to half-relaxation and half-decay of [Ca++]i were not altered significantly after treatment with CPA. These findings provide evidence that the SERCA plays a functional role in the frequency-dependent increase in force of contraction in human myocardium. Because an impaired function of the SERCA is predominantly followed by alterations of inotropic and to a lesser degree of lusitropic function, other important factors to lower [Ca++]i and influence relaxation may be present in human myocardium to compensate for the reduced SERCA activity, e.g., Na+-Ca++ exchanger.
本研究调查了肌浆网Ca++-ATP酶在人类心肌收缩与舒张、细胞内Ca++瞬变以及力-频率关系中的功能作用。在环匹阿尼酸（CPA，0 - 30 μM）存在的情况下，测量了从非衰竭供体心脏（n = 7）获取的肌浆网（SR）分离出的膜囊泡的Ca++-ATP酶活性，CPA是SR（SERCA）的Ca++-ATP酶的一种高度特异性抑制剂。研究了CPA对人类非衰竭心肌分离的左心室肌条收缩与舒张参数、力-频率关系以及[Ca++]i瞬变（使用fura-2）的影响。CPA浓度依赖性地抑制分离的SR囊泡的SERCA活性。在CPA（30 μM）存在的情况下，人类左心室非衰竭心肌先前的正力-频率关系变为负性。特别是在高刺激频率下，CPA降低了舒张张力、张力上升峰值速率和收缩期fura-2发光，而张力峰值时间、[Ca++]i峰值时间、95%舒张时间、舒张期张力和舒张期Ca++水平增加。CPA处理后，张力衰减峰值速率以及[Ca++]i半舒张时间和半衰减时间没有显著改变。这些发现提供了证据，表明SERCA在人类心肌收缩力的频率依赖性增加中发挥功能作用。由于SERCA功能受损主要会导致变力功能改变，而松弛功能改变程度较小，人类心肌中可能存在其他降低[Ca++]i并影响舒张的重要因素，以补偿SERCA活性降低，例如钠-钙交换体。
