| Research Abstract |
Rat peritoneal mast cells have two activation pathway, an lgE-dependent pathway and an lgE-independent, pertussis toxin-sensitive G-protein (Gi) pathway. GlcNAc-oligomer specific lectin Datura stramonium agglutin (DSA) is one of the agonists of the lgE-independent action sites (putative recepotor) of the Gi-protein pathway. Their initial activation induced by DSA was a transient increase of intracellular calcium concentration followed by assembly of cytoskeleton as was compound 48/80 (48/80) by the method of confocal fluorescence microscopic analysis. Mast cell activation induced by DSA was sugar-specific and inhibited by other GlcNAc-specific lectins, such as WGA, STA and LEA, but not by ConA.Antagonist lectins bound to the corresponding glycoproteins and did not activate the Gi-protein pathway by themselves, but interfered with the interaction between the glycoproteins and DSA.The basic releasers 48/80, PE16 and bradykinin additively enhanced the histamine release induced by DSA, sug
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gesting that they share the same mechanisms of action, in which glycoproteins containing GlcNAc-residues were involved. Cationic benzalkonium chloride, an antagonist of Gi, irreversively inhibited the histamine release induced by DSA, but anionic polymer haparin did not. However, the histamine release induced by 48/80 or PE16 was inhibited by benzalkonium chloride and aniomic polymers (heparin, de-N-sulfated heparin, poly-aspartic acid, and poly-glutamic acid). Sialic acid was also important, since MAM (sialic acid-specific lectin) and neuraminidase inhibited the histamine release induced by DSA, 48/80, PE16, substance P and bradykinin. We stained the glycoproteins of rat peritoneal mast cells. At least four glycoproteins with affinity to DSA, WGA and MAM, and sensitive to neuraminidase-treatment were detected by lectin-blotting. Some of them may be putative receptors coupled to histamine release including the Gi-protein pathway. These studies may have important implications of the development of therapeutically useful inhibitors and antagonists. Less
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