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

Abstract

The aim of the present work was to assess the effect of various drugs applied locally on the pH of the luminal fluid (pHlum) in guinea pig endolymphatic sac. pHlum and transepithelial potential, when measured in vivo by means of double-barrelled pH-sensitive microelectrodes, were 7.06 ± 0.08 and +6.1 ± 0.34 mV (mean ± SE; n = 84), respectively, which is consistent with a net acid secretion in the luminal fluid of the endolymphatic sac. Bafilomycin and acetazolamide increased and decreased, respectively, pHlum. Amiloride, ethylisopropylamiloride, ouabain, and Schering 28080 had no effect on pHlum. Results obtained with inhibitors of anionic transport systems were inconclusive; e.g., DIDS reduced pHlum, whereas neither SITS nor triflocin had any effect. We conclude that bafilomycin-sensitive H+-ATPase activity accounts for the transepithelial acid gradient measured in the endolymphatic sac and that intracellular and membrane-bound carbonic anhydrase probably participates in regulating endolymphatic sac pHlum. The relationship between acid pH, endolymph volume, and Ménière's disease remains to be further investigated.