AJP - Cell Physiology, Vol 251, Issue 5 787-C794, Copyright © 1986 by American Physiological Society
Embryonic chick allantois: functional isolation and development of sodium transport
J. S. Graves, B. E. Dunn and S. C. Brown
By removing the shell membranes from the chorioallantoic membrane, the
chorion is damaged, as visualized by electron microscopy, and rendered
permeable, as evidenced by penetration of horseradish peroxidase and
increased inhibition of the allantoic Na+-K+ pump by ouabain applied on the
chorionic side. The short-circuit current (SCC) of this functionally
isolated allantoic epithelium is augmented by nystatin, a channel-forming
ionophore, when applied to the mucosal surface. Electrical parameters were
determined for three age groups between 12 and 19 days of incubation. The
SCC approximately doubled from the youngest (12-13 days) to the oldest
(18-19 days) groups, whereas the transepithelial resistance (Re) of 700-900
omega X cm2 remained the same. Amiloride, an inhibitor of apical Na+
uptake, inhibited 98-100% of the SCC at 10(-4) M in both 15-16 and 18-19
day epithelia. In the 12- to 13-day preparation 20-25% of the SCC was
insensitive to 10(-3) M amiloride. The Ki's for amiloride were similar in
all preparations, at about 5 X 10(-7) M. Determination of the Hill
coefficients for inhibition revealed a lower value (0.75 +/- 0.03) for the
12-13 day preparation compared with the two older preparations with
coefficients not significantly different from unity. Replacing Na+ in the
bathing solutions abolished the SCC of 18-19 day epithelia, whereas about
15% of the SCC remained at 12-13 days. Thus, during development, the SCC of
the allantoic epithelium increases in magnitude and becomes increasingly
(to 100%) amiloride-sensitive and Na+-dependent.
