Calmodulin in mast cells and its role in histamine secretion

Calmodulin content and distribution in rat peritoneal mast cells was determined by radioimmunoassay. Isolated pure mast cells were disrupted by sonication and the total calmodulin content and its distribution were determined. Calmodulin bound to the membranes was released by heating with 0.1% Lubrol PX to 95 degrees C for 5 min. The total calmodulin content of mast cells was found to be 160 +/- 14 ng/10(6) cells (9.4 +/- 0.82 pmoles/10(6) cells). The highest amount (68%) was present in the supernatant representing the cytosol. The next highest amount (26%) was found in the composite fraction consisting of mitochondria, endoplasmic reticulum, Golgi vesicles and plasma membrane (100,000 g pellet). The mast cell granules contained 4% of the total calmodulin. Trifluoperazine (TFP) was used as an antagonist to explore the role of calmodulin in histamine secretion. At 10 microM concentration, TFP caused a negligible spontaneous histamine release by its membrane effect. TFP (10 microM) inhibited histamine release by all the three secretagogues used, but the degree of inhibition varied: 60% with antigen, 40% with compound 48/80 and 20% with ionophore A23187. It is suggested that the TFP effect is due to calmodulin-antagonism and interference with the activation of enzymes, essential to the secretory process.