Complex Response of Epithelial Cells to Inhibition of Na(+) Transport by Amiloride
WALTER REED ARMY INST OF RESEARCH WASHINGTON DC
Pagination or Media Count:
When toad urinary bladder or frog skin epithelia are treated with amiloride, short-circuit current I sub sc, which represents the net active transepithelial sodium cation transport rate from the apical to basolateral surface, decreases rapidly2-5 to approx. 15-20 of control values and then slowly, over several minutes, continues falling toward zero. The contribution of this second phase of the decline is dependent on the transporting condition of the tissue before administration of amiloride. Attenuation of the second phase was observed if tissues were subjected to a period of transport inhibition. Tissues preincubated in O Na Ringer solution on the apical surface were returned to control Na Ringer, which caused an approx. 25 increase of I sub sc above control values. Immediate reapplication of amiloride caused I sub sc to decrease more rapidly than the previous exposure to values near zero, substantially reducing or eliminating the secondary slow decline. After long- term reincubation of tissues in control, 100 mM Na solution, another treatment with amiloride indicated that the magnitude of the secondary decline increased in frog skin but not in urinary bladder epithelia. We conclude that the effects of amiloride is complex and may cause additional effects besides simply blocking entry of Na into the apical membrane channel, and we suggest that regulatory mechanisms may be invoked in response to transport inhibition. Keywords Electrophysiology Cytoskeleton Short-circuit current, Ion channels, Reprints.