REGULATION MECHANISMS OF INTRACELLULAR PH OF XENOPUS-LAEVIS OOCYTE

Intracellular pH values (pH(i)) of Xenopus oocytes were optically measured using a fluorescent dye, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The oocytes were loaded with dye by incubation with a membrane-permeable form (BCECF-AM). Mean pH(i) of the oocytes in pH 7.6 solution was 7.69. Increasing ambient pCO2 rapidly decreased pH(i) and estimated buffering power was 23.8 mM/pH unit. Changing ambient HCO3- from 5 to 30 mM did not alter pH(i). After incubation in a Na+-free solution, Na+ addition to the bath rapidly increased pH(i) and this response was blocked by amiloride (ED50 2 muM). The addition of NH4Cl to the bath caused an initial transient increase in PH(i) followed by a secondary decrease. The secondary decrease was greatly inhibited by a histidine specific reagent, diethylpyrocarbonate. It was also slightly inhibited by ouabain, Ba2+ and furosemide, but not by amiloride. These data suggest that (1), fluorescence technique is applicable to PH(i) measurements of Xenopus oocytes; (2), Xenopus oocytes have an amiloride sensitive Na+/H+-exchange, and permeabilities to CO2, NH3, and NH4+. These observation may be useful in studying the relationship between pH(i) and oocytes development, and the expression of acid/base transporters in Xenopus oocytes.