AJP - Renal Physiology, Vol 241, Issue 3 315-F321, Copyright © 1981 by American Physiological Society
Potassium absorptive pump at the luminal membrane of turtle urinary bladder
R. F. Husted and P. R. Steinmetz
In the absence of transepithelial electrochemical gradients, the direction
of net K transport across the turtle urinary bladder is from the mucosal
(M) to the serosal (S) solution. Under control conditions, M leads to S
flux was 101 +/- 5 nmol . h-1 . (8 cm2)-1, S leads to M flux was 59 +/- 4,
and the net absorptive flux was 42 +/- 6. The K absorptive pump was
characterized by examining its dependence on voltage and ambient sodium and
its sensitivity to mucosal ouabain. Lumen-negative voltages caused an
increase rather than the expected decrease in active K absorption. Thus,
the active K flux appeared to be coupled to a flow of positive charge in
the opposite direction, possibly representing Na secretion in excess of K
absorption. Net K absorption was abolished by removal of Na from the medium
and by mucosal, but not serosal, addition of ouabain. The reverse
electrogenicity, Na dependence, and ouabain sensitivity of K absorption
indicate that the K pump of the mucosal membrane has characteristics of a
Na-K-ATPase.
