Involvement of Na⁺-H⁺ Exchange in Intracellular pH Recovery from Acid Load in the Stria Vascularis of the Guinea-pig Cochlea

Abstract

The effect of acid load by NH₄⁺ prepulse method on intracellular pH (pHi) and Na concentration ([Na⁺]i) in the stria vascularis tissue was studied using fluorescence ratio image microscopy. The pHi and [Na⁺]i were determined with fluorescence indicator dyes, 2′,7′-bis(2-carboxyethyl)-5,6-carboxyfluorescein and sodium-binding benzofuran isophthalate, respectively. Intracellular acidification from the basal pHi of 7.12 ± 0.08 to 6.82 ± 0.08 was induced by NH₄⁺ prepulse. Subsequent addition to the standard NaCl solution gradually increased pHi to the control value. This Na⁺-induced pHi recovery was significantly inhibited by the presence of amiloride and absence of external Na⁺. Basal free [Na⁺]i was 19 ± 5 mM in the stria vascularis. In the same maneuver of acid load, the pHi recovery was associated with the increase in [Na⁺]i sensitive to the amiloride derivative. Thus, the process of the pHi recovery from acid load was demonstrated to involve the Na ⁺- H⁺ exchange in the stria vascularis.

Key Words:

• Na⁺-H⁺ exchange
• intracellular pH
• intracellular Na⁺
• BCECF
• SBFI
• fluorescence microscopy
• stria vascularis
• amiloride