Mast cells taken from the peritoneum of the rat can be induced to secrete their histamine by a variety of stimuli: antigen-antibody reactions, dextran or concanavaiin A. The secretion is accompanied by an uptake of 45calcium . The two processes are closely coupled: (1) They are linearly related; 10% histamine secretion corresponds to a calcium uptake of about 0.08 fmol/cell. (2) They have similar time courses; both are complete within 1 rain. (3) They are both similarly dependent upon pH; with a maximum at 7.5. (4) They are both similarly dependent upon antigen concentration over the range 10 -s to 10 -3. (5) Phosphatidyl serine increases both processes whereas dibutyryl cAMP and theophylline inhibit them.
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