Role of Intracellular Buffering Power on the Mitochondria-Cytosol pH Gradient in the Rat Liver Perfused at 4°C

详细信息    查看全文

• 作者：Durand ; Thierry ; Delmas-Beauvieux ; Marie-Christine ; Canioni ; Paul ; Gallis ; Jean-Louis
• 刊名：Cryobiology
• 出版年：1999
• 出版时间：February, 1999
• 年：1999
• 卷：38
• 期：1
• 页码：68-80
• 全文大小：121 K

文摘

The factors regulating the amplitude and the pH gradient between cytosol and mitochondria (ΔpH_mito-cyt) were investigated in the isolated rat liver perfused at 4°C. Liver ATP content, pH, and buffering power of cytosolic and mitochondrial compartments were evaluatedin situusing phosphorus-31 nuclear magnetic resonance spectroscopy. No ΔpH_mito-cytwas detected in the liver perfused without bicarbonate. Permeant weak acid in the perfusate (H₂CO₃, 25 mM, or isobutyric acid, 25, 50, or 100 mM) acidified both cytosol and mitochondria and revealed a ΔpH_mito-cytfrom 0.06 to 0.31 pH unit. Nevertheless, the manipulations of the ΔpH_mito-cytwere more effective under bicarbonate-free conditions, due to the absence of buffering by H₂CO₃/HCO⁻₃. In the absence of bicarbonate, the intracellular buffering power was threefold higher in the mitochondria (110 mmol/pH unit at pH_mito7.16) than in the cytosol (44 mmol/pH unit at pH_cyt7.30) and dependent on the matrix and cytosol pH, respectively. These buffering powers were almost double in the presence of bicarbonate. In the bicarbonate-free perfused liver, the respiratory activity was 0.08 ± 0.02 μmol O₂/min · g liver wet weight and the ATP turnover was only 40 ± 7 nmol/min · g liver wet weight, indicating the weak activity of liver mitochondria when ΔpH_mito-cytwas <0.05 pH unit. The ATP turnover during a 50 mM isobutyric acid load was 35 ± 4 nmol/min · g liver wet weight whereas ΔpH_mito-cytrose to 0.26 ± 0.02 pH unit and pH_mitoremained alkaline. Hence, although ΔpH_mito-cytwas increased the ATP turnover remained unchanged. This work is the first evaluation of the mitochondrial buffering power in the isolated liver. The ΔpH_mito-cytobserved within various acid loads reflected the differential titration of cytosol and mitochondria containing proteins and H₂CO₃/HCO⁻₃buffering systems. Moreover, no direct relationship between ΔpH_mito-cytand ATP turnover could be shown.