Polyethylenimine with a molecular weight of 600 (PEI6) was the simplest and the most useful to investigate mast cell-activating mechanisms via pertussis toxin (IAP)-sensitive G protein pathway. 2. IAP, lidocaine, or dibutyryl cyclic AMP were inhibitors of the histamine release induced by PEI6, but anti-allergic drug DSCG, the calcium antagonist, D-600, kinase inhibitors, H-7 and K252a, or the calmodulin inhibitor, W-7 were not. 3. The additive effects of compound 48/80 and PEI6 suggested that the action sites for PEI6 overlapped the binding sites of compound 48/80. 4. Mast cell activation induced by PEI6 was sugar-specifically inhibited by N-acetylglucosamine(Glc-NAc)-specific lectins and/or by sialic acid (Sia)-specific lectins, suggesting that the action sites for PEI6 were glycoproteins having GlcNAc and/or Sia residues. 5. Four glycoproteins seemed to be involved in histamine release, including the IAP-sensitive G-protein pathway.
