AJP - Renal Physiology, Vol 248, Issue 2 308-F313, Copyright © 1985 by American Physiological Society
Determination of the sodium transport pool in epithelia from tracer fluxes: a simplified approach
K. Turnheim and H. Plass
The epithelial content of tracer Na can be calculated either from the
exponential increase of unidirectional transepithelial Na tracer fluxes
observed after addition of labeled Na to the solution bathing the luminal
side of isolated epithelia or from the linear portion of the rate of
accumulation of label in the serosal solution. The second method is not
only simpler, because fewer data points are required and no logarithmic
transformations are necessary, but also more accurate, as shown in
experiments with stripped epithelia of rabbit descending colon. From the
difference in tissue Na tracer content in the absence and presence of
amiloride, which blocks luminal Na uptake, a Na concentration in the
transport pool of 8-10 mM is obtained, assuming that all cells participate
in active transport. From a comparison of the intracellular Na
concentration derived from current-voltage relations of the apical Na entry
step with the Na concentration in the epithelial Na transport pool, an
estimate may be obtained of what fraction of the cell mass is involved in
active Na transport.
