EFFECT OF LOCALLY APPLIED DRUGS ON THE ENDOLYMPHATIC SAC POTENTIAL

In Meniere disease, an inner ear disorder related to an endolymphatic hydrops, an alteration of the functioning of the endolymphatic sac has been proposed The endolymphatic sac is assumed to he involved in the secretion/resorption of endolymph, The epithelial transport systems ha ve been indirectly studied by the recording of the endolymphatic sac t ransepithelial. po tential (ESP) in control conditions and after the l ocal injection of drugs such as diuretics that have been pro. posed ii i the treatment of Meniere's disease, The ESP was recorded, in vivo, i ll guinea pigs up to 150 minutes after the perisaccular injection of 5 mu L of a 150 mmol/L (mM) NaCl solution containing various drugs know n to inhibit ionic transport systems, The initial ESP was +8.4 +/- 0.3 mV (mean +/- SEM, n = 78), The basolateral injection of: 5 mu L of 15 0 mM NaCl induced an ESP decrease of 64% +/- 6.0% (n = 12), 5 minutes after the end of the injection, Then ESP increased, returning to its i nitial value at 60 minutes and surpassing it at 120 minutes. Diuretics such as acetazolamide (10(-3) mol/L [M]), an inhibitor of carbonic an hydrase, and amiloride (10(-4) M), an inhibitor of Na channel as Na/H exchanger, decreased the ESP recovery. At variance, bumetanide (10(-6) Ka, 10(-4) M), the Na-K-CI cotransport inhibitor, and chlorothiazide (10(-4) M), a Na-Ca cotransport-inhibitor, failed to alter-the ESP as compared with the control group, Ouabain (10(-3) M), the Na+,H+-adenos ine triphosphatase (ATPase) inhibitor, prevented the ESP recovery othe rwise observed GO minutes after the NaCl injection, Bafilomycin A(1), the inhibitor of the vacuolar-type H+-ATPase, prevented the recovery o f the ESP with a log-dose/effect (10(-5) IM, 10(-6) M, 10(-8) IM), Dis ulfonic acid stilbene (DIDS) (10(-4) M), an inhibitor of transporters involving HCO3-, also prevented tile ESP recovery, These results sugge st that the genesis of the ESP was highly dependent on acid-base trans port systems including carbonic anhydrase, a vacuolar-type H+-ATPase, and an anionic transport system blocked by DIDS. Furl;her studies are needed to confirm the alternation of the acid-base balance in this epi thelium and its possible involvement in the pathogenesis of Menieres d isease.