Permeability and diffusivity of nitric oxide in human plasma and red cells

A simple diffusion cell was made to measure the permeability and diffusivity of Nitric Oxide in human plasma and red cells. Nitric oxide was passed through the cell containing plasma or nitrited red cells enclosed by silicone membranes. Steady state permeability (α_NOD_NO ) was calculated from the cell dimensions and from the NO bulk flow entering and leaving the cell. The diffusion coefficient (D_NO) was calculated in three ways: (i) by dividing the steady state permeability by published values for solubility (α_NO ) in water at 26 °C and 37 °C (ii) by a numerical method and (iii) by an analytical method. Mean steady state permeability (95% confidence intervals) were plasma (26 °C) 5.57 × 10^-11 (2.35 × 10^-11-1.32 × 10^-10) and (37 °C) 5.48 × 10^-11 (2.13 × 10^-11-1.41 × 10^-10) mol cm^-1 s^-1 atm^-1 and red cells (26 °C) 6.74 × 10^-12 (1.29 × 10^-12-3.53 × 10^-11) and (37 °C) 3.93 × 10^-11 (1.39 × 10^-11-1.11.10^-10) mol cm^-1 s^-1 atm^-1. Median Diffusion Coefficients (D_NO) for plasma at 37 °C ranged from 3-3.36 × 10^-5 cm² s^-1 and red cells 2.41-2.94 × 10^-5 cm² s^-1 depending on the method used. These values may be used for modelling NO transport in vivo in the human lung and capillary. Parameters used for modelling in vivo should be measured at 37 °C.