title: Inhibition of Na+ flux in Chinese hamster ovary cells and Swiss 3T3 cells by a potent new derivative of amiloride, methylisopropyl-amiloride.
abstract: Amiloride inhibits the mitogen-stimulated Na+ influx of cultured fibroblasts with very low affinity. We have therefore analyzed eight new derivatives of amiloride for their efficacies of inhibiting the Na+ flux in Chinese hamster ovary cells (CHO-K1). Four of these analogs demonstrate markedly enhanced potencies relative to amiloride. One of the derivatives, methylisopropyl-amiloride (MIA), is approximately 900-fold more potent (ID50 = 42 nM) than amiloride in inhibiting Na+ uptake of these cells. Inasmuch as external Na+ ions antagonize amiloride inhibition of Na+ influx competitively, we investigated the ability of MIA to inhibit Na+ flux in the absence of external Na+ ions. The ID50 value determined for MIA inhibition of CHO-K1 cell Na+ efflux from Na+-loaded cells into Na+-free media is 15 nM. We also examined the efficacy of MIA for Na+ efflux inhibition in a nontransformed fibroblast cell line, Swiss 3T3. The ID50 value for inhibition of Na+ efflux from 3T3 cells is comparable to that for CHO-K1 cells. Thus, we have identified a highly potent derivative of amiloride, MIA, that inhibits Na+ flux at nanomolar concentrations in both a transformed and a nontransformed cell line. It is possible that MIA may serve as a useful tool for biochemical characterization of the mitogen-stimulated Na+ transporter and for assessment of the role of this transporter in mitogenesis.
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001790:Blood Physiological Phenomena; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D005260:Female; D008555:Melitten / Q000494:pharmacology; D009550:Nigericin / Q000494:pharmacology; D010053:Ovary; D011522:Protons; D012964:Sodium / Q000378:metabolism*
chemical_list: D011522:Protons; C048793:methylisopropylamiloride; D008555:Melitten; D000584:Amiloride; D012964:Sodium; D009550:Nigericin