AJP - Renal Physiology, Vol 250, Issue 2 273-F281, Copyright © 1986 by American Physiological Society
Stimulation of apical Na permeability and basolateral Na pump of toad urinary bladder by aldosterone
L. G. Palmer and N. Speez
The effect of aldosterone on Na entry and Na exit from the toad urinary
bladder epithelium was studied using current-voltage analysis of the apical
cell membrane to measure apical Na permeability (PNa) and the intracellular
Na activity (Nac). Varying the activity of Na in the mucosal solution
elicited parallel changes in active Na transport (INa) and Nac, allowing
the activation of the basolateral Na pump by Nac to be evaluated. Five
hours after addition of aldosterone, INa increased 130% and PNa increased
140% relative to controls. The pump rate at an arbitrarily chosen value of
Nac = 4 mM [Ip(4)] increased 53%. Eighteen hours after addition of the
hormone, INa increased 500%, PNa increased 680%, and Ip(4) increased 110%.
ADH increased INa and PNa without changing Ip(4), whereas KCN decreased all
three parameters. A change in the activation curve for the pump induced by
aldosterone was also observed in the presence of mucosal nystatin, which
permeabilized the apical membrane, allowing Nac to be controlled. Attempts
to distinguish an effect on the maximal pump rate from one on the affinity
for Na were equivocal. The results imply that aldosterone has independent
stimulatory effects on Na entry across the apical membrane and Na exit
across the basolateral membrane but that the stimulation of the entry
process is considerably stronger.
