guanosine-5--o-(3-thiotriphosphate) and Adenoma

The role of GTP on somatostatin-induced K+ current increase was examined in dissociated human pituitary tumor cells obtained from three acromegalic patients. Pituitary cells in culture were voltage-clamped by using the patch clamp technique in the whole-cell configuration. Somatostatin (100 nM) increased the membrane permeability to K+ ions and inhibited hormone secretion. A current-voltage relation of the somatostatin-induced K+ current showed an inward rectification when the concentration of extracellular K+ ions was increased. The amplitude of the somatostatin-induced K+ current decreased during recording when the patch pipette solution did not contain GTP; addition of 100 microM GTP to the patch pipette solution prevented this reduction. Intracellular application of 100 microM guanosine 5'-[gamma-thio]triphosphate (GTP[gamma S] evoked an inward rectifying K+ conductance in the absence of somatostatin. After the GTP[gamma S]-induced K+ conductance reached a steady level, application of somatostatin did not further increase the K+ conductance. In pertussis toxin-treated cells GTP[gamma S] did not evoke K+ conductance. It was concluded that somatostatin-induced K+ channels were regulated by a GTP-binding protein.

Topics: Acromegaly; Adenoma; Drug Interactions; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Humans; Membrane Potentials; Pertussis Toxin; Pituitary Neoplasms; Potassium; Somatostatin; Thionucleotides; Tumor Cells, Cultured; Virulence Factors, Bordetella

Topics: Adenoma; Adenylyl Cyclases; Adolescent; Adult; Aged; Alprostadil; Child; Enzyme Activation; Female; Goiter, Nodular; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Humans; Male; Middle Aged; Prostaglandins E; Receptors, Cell Surface; Receptors, Thyrotropin; Sodium Fluoride; Stimulation, Chemical; Thionucleotides; Thyroid Diseases; Thyroid Neoplasms