Swärd K, Josefsson M, Lydrup M L, Hellstrand P
Department of Physiology and Biophysics, University of Lund, Sweden.
Acta Physiol Scand. 1993 Jul;148(3):265-72. doi: 10.1111/j.1748-1716.1993.tb09557.x.
Contractions in the rat portal vein, evoked by spontaneous action potentials or depolarizing high-K+ solution, are rapidly and reversibly inhibited by hypoxia or respiratory blockade. Intracellular free calcium ([Ca2+]i) was measured using Fura-2 to evaluate the effects of metabolic blockade on excitation-contraction coupling. Spontaneous contractions were associated with transient increases in [Ca2+]i. During exposure to cyanide (0.2-0.4 mM) or 2,4-dinitrophenol (30 microM) the duration and amplitude of the Ca2+ transients were decreased, leading to a decreased mean time integral of the individual [Ca2+]i transient, and corresponding decrease in the duration and amplitude of the contraction. Basal [Ca2+]i was increased in the presence of the metabolic inhibitors. High-K+ (40 mM) contractions caused a sustained increase in [Ca2+]i, which was not inhibited by exposure to cyanide, although the amplitude of the associated contraction was greatly reduced. Together with the earlier demonstration of decreased 20 kD myosin light chain phosphorylation under these conditions, this indicates that the activation of contraction is influenced by metabolism via the energy dependence of the light chain phosphorylation reaction. Thus at least three steps in the excitation-contraction sequence are influenced by inhibition of oxidative metabolism: membrane excitation, light chain phosphorylation, and the cross-bridge cycle. This provides mechanisms for a high degree of metabolic sensitivity of vascular tone, of importance for the adaptation of blood flow to tissue metabolic demands.
由自发性动作电位或去极化高钾溶液诱发的大鼠门静脉收缩，会被缺氧或呼吸阻断迅速且可逆地抑制。使用Fura-2测量细胞内游离钙（[Ca2+]i），以评估代谢阻断对兴奋-收缩偶联的影响。自发性收缩与[Ca2+]i的短暂增加有关。在暴露于氰化物（0.2 - 0.4 mM）或2,4-二硝基苯酚（30 microM）期间，Ca2+瞬变的持续时间和幅度减小，导致单个[Ca2+]i瞬变的平均时间积分降低，以及收缩的持续时间和幅度相应减小。在存在代谢抑制剂的情况下，基础[Ca2+]i升高。高钾（40 mM）收缩导致[Ca2+]i持续增加，尽管相关收缩的幅度大大降低，但暴露于氰化物时并未受到抑制。连同在此条件下早期证明的20 kD肌球蛋白轻链磷酸化减少，这表明收缩的激活通过轻链磷酸化反应的能量依赖性受到代谢的影响。因此，兴奋-收缩序列中的至少三个步骤受到氧化代谢抑制的影响：膜兴奋、轻链磷酸化和横桥循环。这为血管张力的高度代谢敏感性提供了机制，这对于使血流适应组织代谢需求很重要。
