The role of membrane cholesterol in cellular function and dysfunction has been the subject of much inquiry. A few studies have suggested that cholesterol may slow oxygen diffusive transport, altering membrane physical properties and reducing oxygen permeability. The primary experimental technique used in recent years to study membrane oxygen transport is saturation-recovery electron paramagnetic resonance (EPR) oximetry, using spin-label probes targeted to specific regions of a lipid bilayer. The technique has been used, in particular, to assess the influence of cholesterol on oxygen transport and membrane permeability. The reliability of such EPR recordings at the water–lipid interface near the phospholipid headgroups has been challenged by all-atom molecular dynamics (MD) simulation data that show substantive agreement with spin-label probe measurements throughout much of the bilayer. This work uses further MD simulations, with an updated oxygen model, to determine the location of the maximum resistance to permeation and the rate-limiting barrier to oxygen permeation in 1-palmitoyl,2-oleoylphosphatidylcholine (POPC) and POPC/cholesterol bilayers at 25 and 35 °C. The current simulations show a spike of resistance to permeation in the headgroup region that was not detected by EPR but was predicted in early theoretical work by Diamond and Katz. Published experimental nuclear magnetic resonance (NMR) oxygen measurements provide key validation of the MD models and indicate that the positions and relative magnitudes of the phosphatidylcholine resistance peaks are accurate. Consideration of the headgroup-region resistances predicts bilayer permeability coefficients lower than that estimated in EPR studies, giving permeabilities lower than the permeability of unstirred water layers of the same thickness. Here, the permeability of POPC at 35 °C is estimated to be 13 cm/s, compared to 10 cm/s for POPC/cholesterol and 118 cm/s for simulation water layers of similar thickness. The value for POPC is 12 times lower than that estimated from EPR measurements, while the value for POPC/cholesterol is 5 times lower. These findings underscore the value of atomic resolution models for guiding the interpretation of experimental probe-based measurements.

膜胆固醇在细胞功能和功能障碍中的作用一直是许多研究的主题。一些研究表明，胆固醇可能会减缓氧气的扩散运输，改变膜的物理特性并降低氧气的渗透性。近年来用于研究膜氧转运的主要实验技术是饱和恢复电子顺磁共振（EPR）血氧测定法，使用针对脂质双层特定区域的自旋标记探针。该技术特别用于评估胆固醇对氧运输和膜通透性的影响。这种在磷脂头基附近的水-脂质界面处的 EPR 记录的可靠性受到全原子分子动力学 (MD) 模拟数据的挑战，这些数据显示与整个双层的自旋标记探针测量结果基本一致。这项工作使用进一步的 MD 模拟和更新的氧气模型，以确定 25 ℃ 1-棕榈酰，2-油酰磷脂酰胆碱 (POPC) 和 POPC/胆固醇双层中最大渗透阻力的位置以及氧气渗透的限速屏障。和35°C。当前的模拟显示头部区域的渗透阻力出现峰值，EPR 没有检测到这一峰值，但 Diamond 和 Katz 在早期理论工作中预测到了这一峰值。已发表的实验核磁共振 (NMR) 氧测量提供了 MD 模型的关键验证，并表明磷脂酰胆碱抗性峰的位置和相对大小是准确的。考虑头组区域阻力，预测双层渗透系数低于 EPR 研究中估计的值，从而使渗透率低于相同厚度的未搅拌水层的渗透率。此处，POPC 在 35 °C 时的渗透率估计为 13 cm/s，而 POPC/胆固醇的渗透率为 10 cm/s，厚度相似的模拟水层的渗透率为 118 cm/s。POPC 的值比 EPR 测量估计值低 12 倍，而 POPC/胆固醇的值低 5 倍。这些发现强调了原子分辨率模型对于指导基于探针的实验测量的解释的价值。