Potentiation of Dextran‐Induced Histamine Release from Rat Mast Cells by Phosphatidyl Serine

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Abstract
Phosphatidyl serine in 1–50 μg/ml concentrations markedly potentiates histamine release in‐duced by dextranin vitrofrom the mixed peritoneal cells of rats. The release occurs within one‐half minute, thus resembling the anaphylactic histamine release. The histamine release from isolated pure populations of mast cells, which generally respond poorly to dextran, was largely restored by phosphatidyl serine. The media, employed for the isolation of mast cells, viz. serum albumin, Ficol and acacia, were found to inhibit histamine release. The albumin inhibition could be overcome by phopshatidyl serine, which enhanced the release in spite of the presence of albumin. Serum albumin was found to bind phospholipids, an effect which may be related to the inhibition of histamine release caused by albumin. The effect of some inhibitors of the ATPase system was studied. Ouabain in 1–10 mM concentration neither affected the dextran‐induced histamine release nor its potentiation by phopshatidyl serine. Ethacrynic acid (1 mM) had some inhibitory effect on histamine release by dextran alone and dextran + phosphatidyl serine. Oligomycin (1 μg/ml) had very little effect on histamine release induced by dextran alone, but completely blocked the potentiation of histamine release caused by phosphatidyl serine.