I. Fatt et al., NON-STEADY-STATE DIFFUSION IN A MULTILAYERED TISSUE INITIATED BY MANIPULATION OF CHEMICAL ACTIVITY AT THE BOUNDARIES, Biophysical journal, 74(1), 1998, pp. 475-486
Diffusion of ionic and nonionic species in multilayered tissues plays
an important role in the metabolic processes that take place in these
tissues. To create a mathematical model of these diffusion processes,
we have chosen as an example hydrogen-bicarbonate ion pair diffusion w
ithin the mammalian cornea. This choice was based on the availability
of experimental data on this system. The diffusion coefficient of the
hydrogen-bicarbonate ion pair in corneal stroma and epithelium is calc
ulated from the observed change in pH in the stroma when conditions at
the corneal anterior epithelial surface are changed while the posteri
or surface is continually bathed with a Ringer's solution in equilibri
um with a CO2-gas air mixture. Matching experimental results to a math
ematical model of the cornea as a two-layer diffusion system yields, a
t 37 degrees C, a diffusion coefficient of the hydrogen-bicarbonate io
n pair of 2.5 x 10(-6) cm(2)/s in the stroma and 0.4 x 10(-6) cm(2)/s
in the epithelium. Application of the Nernst-Einstein equation to thes
e data gives the following diffusion coefficients in the two layers: 1
) stroma, D(H+) = 11.8 x 10(-6) cm(2)/s; D(HCO3-) = 1.5 x 10(-6) cm(2)
/s; and 2) epithelium, D(H+) = 1.9 x 10(-6) cm(2)/s; D(HCO3-) = 0.22 x
10(-6) cm(2)/s.