PH REGULATION OF THE GLOBULAR SUBSTANCE IN THE OTOCONIAL MEMBRANE OF THE GUINEA-PIG INNER-EAR

Physiological and pharmacological characteristics of the globular subs tance, a precursor of otoconia, are not well understood. In the presen t study, we investigated the variations and regulation of internal pH (pH(i)) of the globular substance of the guinea-pig inner ear. The oto conial membrane was dissected out from the utricular macula and loaded with the pH-sensitive fluorophore, carboxyseminaphthorhodafluor-1. Dy namic changes of fluorescence were directly observed under a confocal laser scanning microscope, and pH(i) was calculated from dual emission ratio. In the NaCl standard solution buffered with 5 mM HEPES/Tris at pH 7.4, the pH(i) of the globular substance varied from 6.26 to 8.55 with an average of 7.21 (n = 270). Exposure to 25 mM NH4+ induced a ra pid increase of the pH(i) followed by a slow relaxation. Then, wash-ou t of NH4+ caused a prompt and pronounced acidification followed by a g radual pH(i) recovery to the initial level. This gradual pH(i) recover y was significantly inhibited by the absence of external Na+, indicati ng the presence of an external Na+-dependent H+ extrusion mechanism. T his pH(i) recovery was also inhibited by 1 mM amiloride and 10 mu M l) -6-[ethyl(2-propyl)amino]pyrazine-2-carboxamide. These results suggest the presence of an Na+-H+ exchanger in the globular substance of the guinea pig. However, HCO3--transporting mechanisms were not determined . The working hypothesis for the otoconial formation is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.