NA+/H+ EXCHANGER ACTIVITY IN THE PIG-KIDNEY EPITHELIAL-CELL LINE, LLC-PK1 - INHIBITION BY AMILORIDE AND ITS DERIVATIVES

Rapidly growing pig-kidney-derived epithelial cells, LLC-PK1, lack detectable amiloride-sensitive Na+/H+ exchange activity when assayed directly. A large 22Na uptake is induced when the cells are acid-loaded prior to assay by incubation with buffer containing ammonium chloride or nigericin. The acid-stimulated sodium uptake is sensitive to amiloride, with half-maximal inhibition at 3.5-4.5 μM in buffer containing 15 μM sodium ion. There is simple competitive interaction between amiloride and sodium ion when the amiloride concentration is below 25 μM and the sodium ion concentration is above 20 mM. Derivatives of amiloride which carry substituents on the 5-amino group are 35- to 175-fold more inhibitory than amiloride itself. © 1985 Academic Press, Inc.