Inhibitory effects of amiloride and its analogues on prostaglandin E2-stimulated fluid transport by cultured porcine thyroid cells: evidence for apical membrane Na+ channels

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Abstract
Confluent monolayers of cultured porcine thyroid cells transport fluid from the apical to the basal surface, forming circumscribed zones of detachment (domes) from the culture dish substrate. Fluid transport, as measured by increase in dome height, was stimulated by prostaglandin E2 (PGE2; 1 μmol/l) and inhibited by amiloride (0·1–100 μmol/l). Values of the inhibition constant (Ki) with 95% confidence limits for each of a series of amiloride analogues were: 3′,4′-dichlorobenzamil (DCB), 0·090 (0·045–0·18) μmol/l; 2′,4′;-dimethylbenzamil (DMB), 0·14 (0·074–0·27) μmol/l; amiloride, 0·72 (0·33–1·8) μmol/l; 5-(N,N-hexamethylene)amiloride (HMA), 17 (5·9–43) μmol/l; 5-(N-ethyl-N-isopropyl)amiloride (EIPA), 33 (15–71) μmol/l; and 2-guanidinobenzimidazole, 243 (110–570) μmol/l. Triaminopyrimidine was ineffective at concentrations up to 1 mmol/l. Since DCB and DMB are known to have a higher affinity for Na+ channels, while HMA and EIPA show higher affinity for Na+/H+ antiports, it was concluded that PGE2-stimulated fluid transport involved an apical membrane Na+ channel. Journal of Endocrinology (1989) 123, 93–97

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