Inositol polyphosphates regulate the membrane interactions of the endosomal p100, G-protein-related protein.

The protein, p100, was previously identified as a G-protein related protein that cycles on and off the cytoplasmic face of the endosome membrane (Traub et al., Biochem. J.

Antigen and carbachol mobilize calcium by similar mechanisms in a transfected mast cell line (RBL-2H3 cells) that expresses ml muscarinic receptors.

Because of unresolved questions about the mechanism of Ag-stimulated Ca2+ influx, Ca2+ mobilization in response to carbachol and Ag was compared in transfected rat basophilic RBL-2H3(ml) cells that expressed both Fc epsilon and ml muscarinic receptors. Although the stimulants activated phospholipase C via different coupling mechanisms, a G protein for carbachol or a tyrosine kinase for Ag, they released Ca2+ from the same intracellular pool and used the same or very similar mechanisms for influx of Ca2+ as indicated by the similar patterns of inhibition of uptake of 45Ca2+ by various cations. With both stimulants, influx and sustained increases in free cytosolic Ca2+ ([Ca2+]i) were associated with relatively small increases in inositol 1,4,5-trisphosphate (IP3).

Effects of sodium cromoglycate and nedocromil sodium on histamine secretion from mast cells from various locations.

Nedocromil sodium and sodium cromoglycate inhibited histamine release from rat peritoneal mast cells. Tachyphylaxis was observed with both drugs. The 2 compounds were extremely selective in their action, being less active against peritoneal mast cells from the hamster and completely ineffective against mast cells from the mouse.

Characteristics of histamine secretion induced by neuropeptides: implications for the relevance of peptide-mast cell interactions in allergy and inflammation.

A variety of basic, sensory neuropeptides induced the release of histamine from rat peritoneal mast cells. However, a wide range of other polycationic agents, such as compound 48/80, the mast-cell-degranulating peptide from bee venom and polylysine also activated this cell type. Histamine release induced by all of these agents had characteristic features in common.

Histamine secretion from mast cells stimulated with somatostatin.

Histamine release from isolated mast cells stimulated with somatostatin resembled that induced by other basic agents. The process was rapid, independent of added calcium or phospholipids, non-cytotoxic, species and tissue specific, not mediated through cell-fixed antibodies or glucoreceptors, and inhibited by antagonists of the polyamine receptor. Somatostatin and other polycations may then act through a common receptor or binding site on the mast cell membrane.