AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 3 402-R409, Copyright © 1987 by American Physiological Society
Ouabain binding in tadpole ventral skin. I. Kinetics and effect on intracellular ions
D. H. Robinson and J. W. Mills
The short-circuit current across tadpole skin is inhibited by only 50%
after 2 h of exposure to 10(-2) M ouabain [Am. J. Physiol. 237 (Regulatory
Integrative Comp. Physiol. 6): R74-R79, 1979]. To determine the Na pump
sensitivity to ouabain, the kinetics of ouabain binding in tadpole
epidermis and the effect of ouabain on intracellular Na and K were tested.
In tadpole epidermis a high-affinity dissociation constant (KD) for ouabain
of 1.21 +/- 0.20 X 10(-7) M was found, which is similar to the KD in frog
skin (1.27 +/- 0.16 X 10(-7) M). Incubation of tadpole epidermis in ouabain
for 1 h increased intracellular Na concentration from 48.8 +/- 3.3 to 66.2
+/- 4.9 mM (P less than 0.005) and decreased K concentration from 115 +/- 7
to 104 +/- 9 mM (P less than 0.01). Two hours of ouabain exposure increased
intracellular Na concentration from 41.4 +/- 2.4 to 73.3 +/- 4.3 mM (P less
than 0.0005) and decreased K concentration from 113 +/- 10 to 85.9 +/- 5.3
mM (P less than 0.05). Regression analysis of the change in Na and K
concentrations reveals a slope of 14.7 +/- 2.5 mM/h for the Na gain, which
is similar in magnitude to the rate of K decrease (-13.8 +/- 4.7 mM/h). It
is hypothesized that the residual short-circuit current seen in tadpole
skin after ouabain exposure is a result of current being carried through
the tissue by a slow gain of Na across the apical membrane and an
equivalent loss of K across the basolateral membrane.
