AJP - Renal Physiology, Vol 250, Issue 1 120-F126, Copyright © 1986 by American Physiological Society
Patterns of K+ permeation following inhibition of Na+ transport in rabbit cortical collecting tubule
J. B. Stokes
The passive (lumen-to-bath) K+ permeation (KK) of rabbit cortical
collecting tubules was measured before and after inhibition of Na+
transport. Inhibition of the Na-K pump with ouabain reduced KK. This result
contrasts sharply with the previously described increase in KK observed
following inhibition of Na+ transport with amiloride. These opposite
changes in KK are owing to the fact that a substantial component of the
lumen-to-bath K+ permeation involves a transcellular pathway. Amiloride,
because it hyperpolarizes the apical membrane, increases KK; ouabain,
because it depolarizes the cell, decreases KK. Previous results have also
suggested that the cell K+ permeability is secondarily altered by these
agents so that the changes in voltage and permeability are additive. These
patterns of changes in KK were used to evaluate the mechanism of action of
two agents that partially inhibit Na+ transport: vasopressin and
prostaglandin (PG) E2. Their effect on KK was qualitatively similar to that
of amiloride. In amiloride-treated tubules, neither vasopressin nor PGE2
altered KK. Neither did they alter the normal reduction in KK caused by
pump inhibition. Thus they did not have any direct effect on K+
permeability. These results are consistent with the thesis that vasopressin
and PGE2 inhibit Na+ absorption by reducing apical membrane permeability.
The relation between the regulation of Na+ absorption and K+ permeation may
have important implications for the regulation of K+ secretion by the
cortical collecting tubule.
