Pertussis toxin distinguishes between muscarinic receptor‐mediated inhibition of adenylate cyclase and stimulation of phosphoinositide hydrolysis in Flow 9000 cells

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Abstract
Pretreatment of human embryonic pituitary tumour cells (Flow 9000) with pertussis toxin significantly reduced carbachol‐mediated inhibition of isoprenaline and prostaglandin E2 stimulation of cyclic AMP formation. This is in accord with an action on the inhibitory Gi‐protein by pertussis toxin. In contrast, pertussis toxin‐pretreatment had no effect on either muscarinic agonist or GTP[S] (a non‐hydrolysable GTP analogue) stimulation of [3H]inositol phosphate production in intact and permeabilized [3H]inositol‐prelabelled Flow 9000 cells, respectively. These results suggest that muscarinic receptors are linked to the inhibition of adenylate cyclase and the stimulation of phosphoinositidase C via two different G‐proteins in Flow 9000 cells.