AJP - Cell Physiology, Vol 236, Issue 1 87-C95, Copyright © 1979 by American Physiological Society
Cation exchange and glycoside binding in cultured rat heart cells
D. McCall
The Na/K-exchange characteristics, ouabain-binding kinetics, and Na pump
turnover rates of synchronously contracting monolayers of neonatal rat
myocardial cells were studied. The cells exchange Na rapidly (T1/2 = 35 s)
with a mean Na flux of approximately 25 (pmol/cm2)/s. The half time (T1/2)
of K exchange is much longer (12 min); the mean K flux is 13 (pmol/cm2)/s.
Active Na/K transport, as measured by K influx, is relatively ouabain
sensitive, and 10(-6) M ouabain produces half-maximal inhibition. Ouabain
(10(-2)M) inhibits 60% of the Na efflux and 75% of the K influx. The cells
bind [3H]ouabain rapidly (T1/2 = 8 min), but release it very slowly (T1/2 =
11 h), and both the amount bound and the rate of binding were inversely
proportional to extracellular K. Specific [3H]ouabain binding demonstrates
saturation reaching a maximum of 1.6 x 10(6) molecules per cell at 2 x
10(-7) M [3H]ouabain. From cell surface area and ouabain-sensitive flux
measurements, the Na pump density was calculated at 720/micrometer2 with an
individual pump turnover rate of 50/s. Thus the studies indicate that
despite their neonatal origin, the behavior of the Na pump in these cells
is very similar to that in other mammalian tissues.
