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The existence and importance of the Na⁺/H⁺ exchanger in intracellular pH (pH_i) regulation in ovarian cells was studied in acid-loaded avian granulosa cells by monitoring the recovery of normal pH_i using a trapped fluorescein derivative as an indicator. The resting pH_i of freshly isolated granulosa cells from preovulatory follicles was 680 ± 0·08 when the extracellular pH (pH_o) and sodium concentration (Na_o⁺) were 7·3 and 144 mmol/l respectively. While exposure of granulosa cells to high pH_o (pH_o > 745) medium shifted the pH_i upward with time, incubation of the cells in low pH_o (pH < 6·80) buffer resulted in a significant decrease in pH_i. In contrast, pH_i remained constant when pH_o was varied between the broad range of 6·8–7·4. When the cytoplasm was acidified by treatment with nigericin in choline⁺ buffer, both the magnitude and rate of recovery of normal pH_i was suppressed significantly with decreasing pH_o, but increased in high pH_o medium. The recovery of pH_i was dependent upon the concentration of extracellular sodium, in that the recovery rate and magnitude increased concomitantly with increases in Na_o⁺ concentrations, while the recovery was abolished when Na_o⁺ was completely replaced with choline⁺. In addition, the sodium ionophore monensin enhanced the recovery rate of normal pH_i in a concentration-dependent manner. This action of monensin was observed only when sodium was present in the incubation medium, indicating that Na_o⁺ entry is important for the recovery of normal pH_i. Monensin also evoked further cytoplasmic alkalinization in fully recovered cells, with a relative net effect dependent upon the level of Na_o⁺ present. The recovery of pH_i by acid-loaded cells was attenuated in a concentration-dependent manner by the Na⁺/H⁺ exchange inhibitor amiloride. These results clearly demonstrate in granulosa cells the presence of a pH_i-regulating system that requires extracellular Na⁺ and is sensitive to amiloride.

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				G. FitzHarris and J. M. Baltz Granulosa cells regulate intracellular pH of the murine growing oocyte via gap junctions: development of independent homeostasis during oocyte growth Development, February 15, 2006; 133(4): 591 - 599. [Abstract] [Full Text] [PDF]