Regulation mechanisms of intracellular pH of Xenopus laevis oocyte.
Intracellular pH values (pHi) 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 pHi of the oocytes in pH 7.6 solution was 7.69. Increasing ambient pCO2 rapidly decreased pHi and estimated buffering power was 23.8 mM/pH unit. Changing ambient HCO3- from 5 to 30 mM did not alter pHi. After incubation in a Na(+)-free solution, Na+ addition to the bath rapidly increased pHi and this response was blocked by amiloride (ED50 2 microM). The addition of NH4Cl to the bath caused an initial transient increase in PHi 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 PHi measurements of Xenopus oocytes; (2), Xenopus oocytes have an amiloride sensitive Na+/H(+)-exchange, and permeabilities to CO2, NH3, and NH+4. These observation may be useful in studying the relationship between pHi and oocytes development, and the expression of acid/base transporters in Xenopus oocytes.
Sasaki
S
S
Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan.
Ishibashi
K
K
Nagai
T
T
Marumo
F
F
D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002463:Cell Membrane Permeability; D005452:Fluoresceins; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009865:Oocytes / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014982:Xenopus laevis
D001639:Bicarbonates; D005452:Fluoresceins; D002245:Carbon Dioxide; D000641:Ammonia; D006859:Hydrogen; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium