Dutta A, Popel A S
Department of Biomedical Engineering, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA.
J Theor Biol. 1995 Oct 21;176(4):433-45. doi: 10.1006/jtbi.1995.0211.
Oxygen diffusion rates within cells may be heterogeneous, with more rapid diffusion occurring along intracellular pathways of high oxygen solubility, such as mitochondria. Recent experimental data indicate that tissue oxygen permeability rises sharply in a temperature range associated with phase transitions in lipid membranes suggesting that membranes may function as oxygen "pathway". The experimental data have been analyzed using theoretical models of diffusion in two-phase media. By assuming muscles to be composed entirely of aqueous cytosol and lipids, cytosolic permeability was determined as a function of temperature by matching the experimental values of tissue permeability with those of model predictions using in vitro values of lipid permeability. Cytosolic permeability ranged from 50% of water permeability (low temperature) to 90% of water permeability (high temperature) and its temperature dependence was distinctly different from that of water. An upper bound for cytosolic permeability was calculated using a physiologic value for protein volume fraction, and lipid permeability was obtained using this cytosolic permeability. A model with a parallel arrangement of lipid and cytosol yielded a value of lipid permeability that was 71% higher than the in vitro value. Intracellular permeabilities calculated from tissue permeability values were found to be inconsistent with experimentally reported values for rat cardiac myocytes. Comparison of three different muscles exhibited the same trend of higher permeability with higher lipid content. It is concluded that both lipid and cytosol permeabilities and, hence, tissue permeabilities are different among different muscles and one should exercise caution when data from one muscle is used to calculate or extrapolate values in other muscles. It is conceivable that muscles with very high mitochondrial content, such as diaphragm and cardiac muscles may exhibit an oxygen permeability which is significantly higher than commonly accepted values. These results warrant additional measurements of tissue oxygen permeability at 37 degrees C, especially for oxidative muscles with high lipid content.
细胞内的氧气扩散速率可能是不均匀的，沿着高氧溶解度的细胞内途径（如线粒体）会发生更快的扩散。最近的实验数据表明，在与脂质膜相变相关的温度范围内，组织氧渗透率会急剧上升，这表明膜可能起到氧气“通道”的作用。已使用两相介质中扩散的理论模型对实验数据进行了分析。通过假设肌肉完全由水性细胞质和脂质组成，通过将组织渗透率的实验值与使用脂质渗透率的体外值的模型预测值相匹配，确定细胞质渗透率是温度的函数。细胞质渗透率范围从水渗透率的50%（低温）到水渗透率的90%（高温），其对温度的依赖性与水明显不同。使用蛋白质体积分数的生理值计算细胞质渗透率的上限，并使用该细胞质渗透率获得脂质渗透率。脂质和细胞质平行排列的模型得出的脂质渗透率值比体外值高71%。从组织渗透率值计算出的细胞内渗透率与大鼠心肌细胞的实验报告值不一致。对三种不同肌肉的比较显示出脂质含量越高渗透率越高的相同趋势。得出的结论是，脂质和细胞质的渗透率以及组织渗透率在不同肌肉之间是不同的，当使用一种肌肉的数据来计算或推断其他肌肉的值时应谨慎。可以想象，线粒体含量非常高的肌肉，如膈肌和心肌，可能表现出明显高于普遍接受值的氧渗透率值。这些结果需要在37摄氏度下对组织氧渗透率进行额外测量，特别是对于脂质含量高的氧化肌肉。
