PT - JOURNAL ARTICLE AU - STEPHEN A. RUDOLPH AU - LINDA R. HEGSTRAND AU - PAUL GREENGARD AU - STEPHEN E. MALAWISTA TI - The Interaction of Colchicine With Hormone-Sensitive Adenylate Cyclase in Human Leukocytes DP - 1979 Nov 01 TA - Molecular Pharmacology PG - 805--812 VI - 16 IP - 3 4099 - http://molpharm.aspetjournals.org/content/16/3/805.short 4100 - http://molpharm.aspetjournals.org/content/16/3/805.full SO - Mol Pharmacol1979 Nov 01; 16 AB - A histamine-sensitive adenylate cyclase was found in human leukocytes and appears to interact with the microtubule system of these cells. Colchicine markedly potentiated the effects of IBMX, histamine, or both on increasing cyclic AMP levels in intact leukocytes. Preincubation with vinblastine or podophyllotoxin caused effects similar to those of colchicine, while lumicolchicine and cytochalasin B were ineffective. Preincubation with colchicine did not significantly affect the concentration of histamine at which half-maximal increases in cyclic AMP levels were attained (5 µM). Membranes prepared from leukocyte homogenates had a basal adenylate cyclase activity of about 10 pmole/min/mg protein; histamine (10-4 M) caused a more than three-fold increase in this activity. The effects of colchicine that were observed with intact cells were not found in the membrane preparation, whether the membranes were prepared from colchicine-treated cells or whether colchicine was added directly to the adenylate cyclase assay mixture. The effects of histamine in both intact cells and cell membranes were blocked by the H2 antagonist metiamide, but not by the H1, antagonist mepyramine. The interaction of histamine with two other hormones that activate leukocyte adenylate cyclase via different receptors, isoproterenol and prostaglandin E1, (PGE1), was also investigated. The effects of all three agonists were not additive with respect to cyclic AMP levels in intact cells, whether in the absence or presence of colchicine, or with respect to adenylate cyclase activity in membrane preparations. Cells enriched for polymorphonuclear or mononuclear leukocytes exhibited responses to histamine, isoproterenol or PGE1, and to colchicine, similar to those seen in the unfractionated leukocyte preparations. The results suggest that interference by colchicine with the organization of cytoplasmic microtubules increases leukocyte adenylate cyclase activity and renders the cells more sensitive to histamine stimulation, without markedly altering the affinity of the histamine receptor. Effects of colchicine were not observed in cell-free preparations, presumably because the interaction between cytoplasmic microtubules and membranes depends upon the integrity of the cell. The non-additivity of the hormone effects suggests that histamine, isoproterenol, and PGE1, may all compete for activation of the same molecules of adenylate cyclase.