PERTUSSIS AND CHOLERA TOXINS INHIBIT PROSTAGLANDIN SYNTHESIS IN RAT ASTROCYTE CULTURES AT DISTINCT METABOLIC STEPS

The influence of pertussis and cholera toxin-sensitive G-proteins in the prostaglandin synthetic pathway has been investigated. Prostaglandin D2 (PGD2) synthesis was stimulated by the calcium ionophore A23187, the phorbol ester tetradecanoylphorbol acetate (TPA), or by extracellular ATP. Pretreatment of cultures with pertussis toxin (Ptx) resulted in a partial inhibition of PGD2 synthesis in both stimulated and unstimulated cells. A23187-stimulated PGD2 synthesis was affected less than ATP- or TPA-stimulated synthesis. Furthermore, Ptx also inhibited A23187-, ATP-, and TPA-stimulated arachidonic acid release. Basal and stimulated PGD2 synthesis were also inhibited, when cultures were preincubated with cholera toxin (Ctx). Here, ATP-stimulated synthesis was affected the most. Arachidonic acid release, in contrast, was enhanced by cholera toxin, even without addition of stimuli. These data suggest that regulation of prostaglandin synthesis in rat astrocyte cultures involves Ptx- and Ctx-sensitive G-proteins. Ptx substrates affect events at or proximal to phospholipase A2, whereas Ctx substrates influence events proximal or distal to phospholipase A2.