Juggi J S
Department of Physiology, Faculty of Medicine, Kuwait University, Safat, Kuwait.
Can J Physiol Pharmacol. 1996 Jan;74(1):116-23.
The recirculation fraction (RF) of the activator Ca2+ of the cardiac muscle is an index of the fraction of the internally released Ca2+ sequestered by the sarcoplasmic reticulum during each contraction-relaxation cycle. Estimates of the RF were obtained by the slope method during the decline of the post-rest potentiation in the isolated aorta-perfused rat heart. Normalized contractile force P(max) of the second post-interval beat, B2, was plotted as a function of the first post-interval beat, B1, and fitted by a linear regression line. The correlation coefficient (r2) and the slope of the line were computed. Under the control experimental perfusion with oxygenated (95% O2-5% CO2) Krebs-Henseleit buffer ([Ca2+]0 1.25 mM, 34 degrees C, ph 7.40), the slope of the line, representing the RF of the rat left ventricle, was 0.73 +/- 0.01 (mean +/- SE) (r2 0.95 +/- 0.01). Increasing the stimulation frequency from 1 to 3.3 Hz produced a negative inotropic effect and significantly reduced the RF, to 0.17 +/- 0.02. Positive inotropic interventions significantly increased the RF, to 0.95 +/- 0.05 with [Ca2+]0 4 mM and to 0.92 +/- 0.04 with a 30% reduction in [Na+]0, whereas inhibition of Ca2+ release from the sarcoplasmic reticulum by ryanodine (1 microM) perfusion significantly reduced the RF, to 0.68 +/- 0.05 from the control ([Ca2+]0 2.5 microM) value of 0.81 +/- 0.05. These findings indicate that RF is a good index of the inotropic status of the rat heart. The time course of changes in RF after graded ischemia-reperfusion indicated a significant increase in the reperfusion RF between 30 and 60 min of ischemia accompanied by a significant rise in left ventricular end-diastolic pressure (LVEDP) and a significant fall in P(max), indicating an irreversible phase of the injury. During the reversible phase ( < 30 min) of the ischemia-reperfusion injury, no significant changes in RF were detected. It was concluded that RF, as derived from the simple interval-force relationship, is a good predictor of the reversible and irreversible phases of the myocardial ischemia-reperfusion injury and index of the extent of Ca2+ loading of the sarcoplasmic reticulum.
心肌激活剂Ca2+的再循环分数（RF）是指在每个收缩-舒张周期中，肌浆网所隔离的细胞内释放Ca2+的分数指标。RF的估算通过斜率法，在离体主动脉灌注大鼠心脏静息后增强下降过程中进行。将第二个间隔期搏动B2的标准化收缩力P(max)作为第一个间隔期搏动B1的函数进行绘制，并通过线性回归线拟合。计算相关系数（r2）和直线斜率。在以含氧（95% O2-5% CO2）的Krebs-Henseleit缓冲液（[Ca2+]0 1.25 mM，34℃，pH 7.40）进行对照实验灌注时，代表大鼠左心室RF的直线斜率为0.73±0.01（平均值±标准误）（r2 0.95±0.01）。将刺激频率从1 Hz增加到3.3 Hz会产生负性肌力作用，并显著降低RF，降至0.17±0.02。正性肌力干预显著增加RF，[Ca2+]0为4 mM时升至0.95±0.05，[Na+]0降低30%时升至0.92±0.04，而通过灌注1 μM兰尼碱抑制肌浆网Ca2+释放会显著降低RF，从对照（[Ca2+]0 2.5 μM）值0.81±0.05降至0.68±0.05。这些发现表明RF是大鼠心脏肌力状态的良好指标。分级缺血-再灌注后RF变化的时间进程表明，缺血30至60分钟之间再灌注RF显著增加，同时左心室舒张末期压力（LVEDP）显著升高，P(max)显著下降，表明损伤进入不可逆阶段。在缺血-再灌注损伤的可逆阶段（<30分钟），未检测到RF有显著变化。得出结论，从简单的间隔-力关系得出的RF是心肌缺血-再灌注损伤可逆和不可逆阶段的良好预测指标，也是肌浆网Ca2+负荷程度的指标。
