2--7--bis(carboxyethyl)-5(6)-carboxyfluorescein and Pituitary-Neoplasms

The effect of mild hyperosmotic stress on cytosolic pH (pHi) alone, and in combination with thyrotropin-releasing hormone (TRH) or the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was investigated in GH4C1 cells at resting pHi. Hyperosmotic stress induced by addition of 50 mM choline was without an effect on pHi. In cells stimulated with either TRH or TPA after choline, pHi increased 0.15 +/- 0.05 and 0.14 +/- 0.03 pH units, respectively (mean +/- SD). A similar response was obtained if TRH or TPA was added prior to choline. The effect was abolished by replacing extracellular Na+ with choline+, and by pretreatment of the cells with amiloride, indicating that the change in pHi probably was dependent on activation of Na+/H+ exchange. The results thus indicate that, in GH4C1 cells, hyperosmotic stress in combination with TRH or TPA can activate Na+/H+ exchange at resting pHi levels.

Topics: Animals; Carrier Proteins; Cell Line; Fluoresceins; Fluorescent Dyes; Hydrogen-Ion Concentration; Kinetics; Osmolar Concentration; Pituitary Neoplasms; Rats; Sodium; Sodium-Hydrogen Exchangers; Tetradecanoylphorbol Acetate; Thyrotropin-Releasing Hormone