The effect of furosemide on sodium movements in human red blood cells.

A study has been made of Na movements in human red blood cells in order to test their sensitivity to inhibition by furosemide or bumetanide. Net changes as well as influx and efflux were measured. Unidirectional Na influx and efflux values confirmed previous evidence for components of both these fluxes sensitive to inhibition by furosemide or bumetanide. The difference between furosemide-sensitive unidirectional influx and efflux was determined at [Na]o 140 mM and shown to be non-significant, even when [Na]i was raised to about 45 mumol ml cells-1. No evidence was found for an influence of furosemide on net movements of Na in cells of either slightly elevated or physiological [Na]i incubated in a 140 mM-Na medium over 4 h. Incubation of cells, under similar conditions, for 12 h did not reveal a bumetanide-sensitive net Na movement. The results suggest that cells with normal or slightly elevated [Na]i, incubated in media of physiological Na concentration, do not possess a mechanism sensitive to inhibition by the loop diuretics that operates to regulate cell Na.