Massari S
Consiglio Nazionale delle Ricerche Unit for the Study of Biomembranes and the Laboratory of Biophysics and Membrane Biology, Department of Biomedical Sciences, University of Padova Medical School, Via Trieste 75, I-35121, Padova, Italy.
J Biol Chem. 1996 Dec 13;271(50):31942-8.
The permeability transition process in rat liver mitochondria was studied by following the swelling consequent to external solute equilibration through the membrane pore. The kinetics of the transition was analyzed according to a model based on the assumptions that the transition rate follows a first-order process and that the solute diffusion rate strongly depends on the pore conformation. Three kinetic parameters, easily calculated from absorbance measurements during mitochondrial swelling, were used to determine whether changes of the swelling rate are due to changes of (i) the transition rate, (ii) the amount of permeabilized mitochondria, (iii) the mean pore dimension, or (iv) the number of pores per mitochondrion. The model was tested for transitions induced either by phenylarsine oxide (PhAsO) or by Ca2+ and Pi. Under both conditions, only a definite fraction of mitochondria was permeabilized, and the transition always followed a first-order reaction, indicating that mitochondria behaved as a homogeneous population. However, the equilibration of external solutes was rapid only in a fraction of permeabilized mitochondria and slow in the remaining fraction, due to restricted solute diffusion through narrower pores. With 0.2 mM PhAsO as the inducer, the fraction of permeabilized mitochondria was about 0.8. Sucrose diffusion was rapid only in 15% of this fraction (half-time less than 1 s) and restricted in the remaining 85% (half-time of about 60 s). Increasing PhAsO concentrations increased the number of pores per mitochondrion and the rate constant of the permeability transition, but not the mean pore diameter and the fraction of permeabilized mitochondria. With 0.28 microM free [Ca2+] and 1 mM Pi as the inducers, the fraction of permeabilized mitochondria was about 0.43. Sucrose diffusion was rapid in 60% of this fraction and restricted in the remaining 40% (half-time of about 9 s). The permeabilization process started above a threshold- free [Ca2+] of 0.15 microM, and the rate constant and the fraction of permeabilized mitochondria reached a maximum at about 0.2 microM, while both parameters were inhibited at higher free [Ca2+].
通过追踪外部溶质通过膜孔达到平衡后线粒体的肿胀情况，研究了大鼠肝线粒体中的通透性转换过程。根据一个模型分析了转换的动力学，该模型基于以下假设：转换速率遵循一级过程，且溶质扩散速率强烈依赖于孔的构象。从线粒体肿胀过程中的吸光度测量值很容易计算出三个动力学参数，用于确定肿胀速率的变化是否归因于以下因素的变化：（i）转换速率；（ii）通透化线粒体的数量；（iii）平均孔径；或（iv）每个线粒体的孔数量。该模型针对由氧化苯胂（PhAsO）或Ca²⁺和Pi诱导的转换进行了测试。在这两种情况下，只有一定比例的线粒体发生了通透化，并且转换始终遵循一级反应，这表明线粒体表现为一个均匀的群体。然而，由于溶质通过较窄的孔扩散受限，外部溶质的平衡仅在一部分通透化的线粒体中迅速发生，而在其余部分则缓慢发生。以0.2 mM PhAsO作为诱导剂时，通透化线粒体的比例约为0.8。蔗糖扩散仅在该部分的15%中迅速发生（半衰期小于1秒），而在其余85%中受限（半衰期约为60秒）。增加PhAsO浓度会增加每个线粒体的孔数量和通透性转换的速率常数，但不会增加平均孔径和通透化线粒体的比例。以0.28 μM游离[Ca²⁺]和1 mM Pi作为诱导剂时，通透化线粒体的比例约为0.43。蔗糖扩散在该部分的60%中迅速发生，而在其余40%中受限（半衰期约为9秒）。通透化过程在游离[Ca²⁺]阈值0.15 μM以上开始，速率常数和通透化线粒体的比例在约0.2 μM时达到最大值，而在较高的游离[Ca²⁺]时这两个参数均受到抑制。
