Role of pertussis toxin sensitive G proteins in the alpha 1 adrenergic receptor but not in the thyrotropin receptor mediated activation of membrane phospholipases and iodide fluxes in FRTL-5 thyroid cells

The regulation of thyroid hormone formation by thyrotropin and norepinephrine involves the activation of both phospholipases C and A2. When FRTL-5 cells are incubated with 10(-10)M pertussis toxin for 4 to 20 h, the stimulation of iodide efflux by norepinephrine is inhibited by 50 to 70%. At the same toxin concentration the norepinephrine induced increase in cytosolic Ca2+ is unaffected; however upon 20 h pretreatment with 10(-9)M pertussis toxin a 30% inhibition is observed. By contrast, the pertussis toxin treatment had no effect on the increase in iodide efflux or in cytosolic Ca2+ levels induced by thyrotropin. Our data suggest that two GTP binding proteins sensitive to pertussis toxin are involved in the alpha 1 adrenergic but not in the thyrotropin induced activation of the signal transduction mechanisms leading to iodide efflux in FRTL-5 cells.