Abstract
The intracellular pH (pHi) of epithelial cells from the endolymphatic sac (ES) of the guinea-pig was measured microfluorometrically with the pH-sensitive fluorescent dye, 2′,7′-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to examine the presence of a Na+-H+ exchanger (NHE) in the ES epithelial cells. pHi recovery from acid loading with an NH4 +-prepulse in a nominally HCO3-free solution was dependent on extracellular Na+ ([Na+]o) and was inhibited by amiloride and its analogue ethylisopropylamiloride (EIPA), suggesting that a decreased pHi induced by an acute acid load may be equilibrated by a NHE. In the steady-state, amiloride had no effect on pHi, indicating that the NHE activity is low at the resting pHi. However, the intracellular acidification induced by the removal of [Na+]o was inhibited by the simultaneous application of amiloride. H+-efflux rate (J H, mean activity of NHE), which was calculated as the product of the recovery rate (dpHi/dt) from the acid loading and the intrinsic buffering capacity (βi) at the corresponding pHi, was decreased as pHi was increased. The concentration/response curve for the inhibition of initial J H by EIPA revealed an apparent 50% inhibitory constant (K i ) of 0.85 µM. Kinetic analysis of initial J H as a function of [Na+]o revealed a Michaelis-Menten constant (K m) of 24.14 mM for Na+-dependent H+ efflux. The results indicate that NHE in the ES epithelium belongs to an amiloride-sensitive subtype.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Author information
Authors and Affiliations
Additional information
Received: 5 August 1997 / Received after revision and accepted: 26 February 1998
Rights and permissions
About this article
Cite this article
Wu, D., Mori, N. Evidence for the presence of a Na+-H+ exchanger in the endolymphatic sac epithelium of guinea-pigs. Pflügers Arch 436, 182–188 (1998). https://doi.org/10.1007/s004240050621
Issue Date:
DOI: https://doi.org/10.1007/s004240050621