Effect of locally applied drugs on the pH of luminal fluid in the endolymphatic sac of guinea pig

The aim of the present work was to assess the effect of various drugs appli ed locally on the pH of the luminal fluid (pH(lum)) in guinea pig endolymph atic sac. pH(lum) and transepithelial potential, when measured in vivo by m eans of double-barrelled pH-sensitive microelectrodes, were 7.06 +/- 0.08 a nd +6.1 +/- 0.34 mV (mean +/- SE; n = 84), respectively, which is consisten t with a net acid secretion in the luminal fluid of the endolymphatic sac. Bafilomycin and acetazolamide increased and decreased, respectively, pH(lum ). Amiloride, ethylisopropylamiloride, ouabain, and Schering 28080 had no e ffect on pH(lum). Results obtained with inhibitors of anionic transport sys tems were inconclusive; e.g., DIDS reduced pH(lum), whereas neither SITS no r triflocin had any effect. We conclude that bafilomycin-sensitive H+-ATPas e activity accounts for the transepithelial acid gradient measured in the e ndolymphatic sac and that intracellular and membrane-bound carbonic anhydra se probably participates in regulating endolymphatic sac pH(lum). The relat ionship between acid pH, endolymph volume, and Meniere's disease remains to be further investigated.