AJP - Cell Physiology, Vol 248, Issue 5 389-C398, Copyright © 1985 by American Physiological Society
Sodium-pump density of cells from dog tracheal mucosa
J. H. Widdicombe, C. B. Basbaum and E. Highland
Uptake of tritiated ouabain by cells isolated from dog tracheal epithelium
showed two components: a saturable component with a Km of 5.1 X 10(-8) M
and a maximal uptake of 8.3 X 10(5) molecules/cell and a nonsaturating
component of uptake that was linear with concentration. Several criteria
indicated that the saturable uptake component represented binding to the
Na+-K+-ATPase. To estimate the average surface area per cell, a known
number of cells were pelleted and weighed, and the average surface area was
calculated, assuming the cells to be perfectly spherical. The validity of
this assumption was confirmed by comparing the calculated surface areas of
cells in isotonic and hypotonic media. From the values for maximal
saturable uptake and average surface area, a pump density of approximately
2,400 sites/micron2 was calculated. Given that the apical membrane lacks Na
pumps and accounts for only approximately 5% of the total surface area,
this value corresponds to the pump density of the basolateral cell
membrane. The pump densities of ciliated, goblet, and basal cells were
compared by autoradiography. The three cell types had approximately the
same density of pump sites.
