Effect of Intravenously Applied Furosemide on Endocochlear DC Potential and Cochlear Microphonics Correlated with Structural Changes in Guinea Pigs
In the scala media, the DC potential of about +80 mV exists between endolymph and neighboring tissue of the earth potential. Furosemide, which is a strong diuretics, is known to inhibit Na-Cl cotransport across the luminar cell of the thick ascending limb of the Henle loop and it produces the changes in cochlear functions. In this study, furosemide was applied systematically at the dosages of 80 mg/kg, 40 mg/kg and 20 mg/kg. Depending upon the doses, furosemide reduced the DC potential to 0 mV or even negative potential and decreased the amplitude of the cochlear microphonics. These changes started within a few min after application of the drug, were maintained another a few min and then recovered completely to the initial level within an hour or so. It is noteworthy to describe that microphonics recovers faster than DC potential. Electronmicroscopic investigation indicated that the shrinkage and projection took place in the cells of stria vascularis. Action of furosemide is explained from the blockage Na-Cl co-transport across the endocochlear side of the marginal cell membrane and, consequently, blockage Na-K pump at the opposite side of the cell membrane.