Higashiyama A, Watkins M W, Chen Z, LeWinter M M
Cardiology Unit, College of Medicine, University of Vermont, Burlington 05405.
Am J Physiol. 1994 Mar;266(3 Pt 2):H1047-54. doi: 10.1152/ajpheart.1994.266.3.H1047.
Myocardial energy consumption for nonmechanical activity (excitation-contraction coupling) has been shown to be length dependent in isolated muscle studies but no more than minimally affected by preload in the whole heart. However, unloaded O2 consumption (VO2, which is used to estimate nonmechanical VO2 in whole heart) may not be accurate for quantifying nonmechanical energy consumption, because it contains VO2 for residual cross-bridge cycling. To more accurately determine the influence of left ventricular (LV) diastolic volume on nonmechanical VO2 in whole heart, we employed a new method for quantifying nonmechanical VO2, using the drug 2,3-butanedione monoxime (BDM). We measured VO2 and force-time integral during infusion of BDM (< or = 5 mM) at high (VH) and low LV volumes (VL) in 16 excised isovolumically contracting red blood cell-perfused rabbit ventricles. LV end-diastolic pressure was 9.7 +/- 4.6 and 3.8 +/- 2.8 (SD) mmHg at VH and VL, respectively. Nonmechanical VO2, estimated as the VO2-axis intercept of the linear VO2-force-time integral relation obtained during BDM infusion, did not differ significantly between VH and VL (0.0137 +/- 0.0083 and 0.0132 +/- 0.0090 ml O2.beat-1 x 100 gLV-1, P = 0.702). A multiple linear regression analysis for the pooled data confirmed this finding (P = 0.361). We conclude that, in the rabbit heart, LV diastolic volume does not importantly affect nonmechanical energy consumption over a physiological range of LV end-diastolic pressure. This indicates that length-dependent activation does not have an energetic cost in whole rabbit heart and suggests that its predominant mechanism is increased Ca2+ affinity for the contractile proteins.
在离体肌肉研究中，已表明心肌用于非机械活动（兴奋 - 收缩偶联）的能量消耗与长度相关，但在完整心脏中，其受前负荷的影响极小。然而，无负荷耗氧量（VO2，用于估计完整心脏中的非机械VO2）可能无法准确量化非机械能消耗，因为它包含残余横桥循环的VO2。为了更准确地确定左心室（LV）舒张容积对完整心脏中非机械VO2的影响，我们采用了一种使用药物2,3 - 丁二酮一肟（BDM）来量化非机械VO2的新方法。我们在16个切除的等容收缩的红细胞灌注兔心室中，于高（VH）和低LV容积（VL）下输注BDM（≤5 mM）期间测量了VO2和力 - 时间积分。VH和VL时的LV舒张末期压力分别为9.7±4.6和3.8±2.8（SD）mmHg。在BDM输注期间获得的线性VO2 - 力 - 时间积分关系的VO2轴截距估计的非机械VO2，在VH和VL之间无显著差异（0.0137±0.0083和0.0132±0.0090 ml O2·beat-1×100 gLV-1，P = 0.702）。对汇总数据的多元线性回归分析证实了这一发现（P = 0.361）。我们得出结论，在兔心脏中，在LV舒张末期压力的生理范围内，LV舒张容积对非机械能消耗没有重要影响。这表明长度依赖性激活在整个兔心脏中没有能量消耗成本，并表明其主要机制是收缩蛋白对Ca2+的亲和力增加。
