The Journal of General Physiology, Vol 72, 513-538, Copyright © 1978 by The Rockefeller University Press
Diffusion of water in cat ventricular myocardium
RE Safford, EA Bassingthwaighte and JB Bassingthwaighte
The rates of diffusion of tritiated water (THO) and [14C]sucrose across cat
right ventricular myocardium were studied at 23 degrees C in an Ussing-type
diffusion cell, recording the time-course of increase in concentration of
tracer in one chamber over 4--6 h after adding tracers to the other.
Sucrose data were fitted with a model for a homogeneous sheet of uneven
thickness in which the tissue is considered to be an array of parallel
independent pathways (parallel pathway model) of varying length. The volume
of the sucrose diffusion space, presumably a wholly extracellular pathway,
was 23% of the tissue or 27.4 +/-1.7% (mean +/- SEM; n=11) of the tissue
water. The effective intramyocardial sucrose diffusion coefficient, D8, was
1.51 +/- 0.19 X 10(-6)cm2.s-1 (n=11). Combining these data with earlier
data, D8 was 22.6 +/- 1.1% (n=95) of the free diffusion coefficient in
aqueous solution D degrees 8. The parallel pathway model and a dead-end
pore model, which might have accounted for intracellular sequestration of
water, gave estimates of DW/D degrees W (observed/free) of 15%. Because
hindrance to water diffusion must be less than for sucrose (where D8/D
degrees 8=22.6%), this showed the inadequacy of these models to account
simultaneously for the diffusional resistance and the tissue water content.
The third or cell-matrix model, a heterogeneous system of permeable cells
arrayed in the extracellular matrix, allowed logical and geometrically
reasonable interpretations of the steady-state data and implied estimates
of DW in the cellular and extracellular fluid of approximately 25% of the
aqueous diffusion coefficient.
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