BLOCKADE OF THE NA+/H+ ANTIPORT ABOLISHES GROWTH FACTOR-INDUCED DNA-SYNTHESIS IN FIBROBLASTS - STRUCTURE-ACTIVITY-RELATIONSHIPS IN THE AMILORIDE SERIES

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 259  (7) , 4313-4319
Abstract
In Chinese hamster lung fibroblasts a growth factor activatable and amiloride-sensitive Na+/H+ antiport was characterized. In this report, the affinity of 28 analogs of amiloride for inhibition of the Na+/H+ antiport and inhibition of growth factor-induced DNA synthesis was compared. The guanidino moiety of amiloride must be protonated to elicit inhibition of the Na+/H+ exchange. Substitutions within this moiety by methyl, phenyl or benzyl groups reduced the activity 20- to 1000-fold. Substitution of the proton(s) of the 5-amino group of amiloride with alkyl or alkenyl groups increases potency up to 100-fold (5-N,N-diethylamiloride has a KI of 4 .times. 10-8 M). In HCO3--free medium and at lower [Na+]0 (25 or 50 mM) to reduce competition with amiloride, growth factor-stimulated DNA synthesis of G0-arrested cells is inhibited by amiloride and its analogs with the same rank order as that for Na+/H+ antiporter inhibition. Over a range of 3 logs of concentration, a tight correlation was established between IC50 [median inhibitory concentration] for the blockade of both processes, Na+/H+ exchange and percentage of cells entering the S phase upon growth factor action. In HCO3--free medium, the functioning of the Na+/H+ exchange system is required for growth factor-induced DNA synthesis.