Influence of CGS 9343B, an inhibitor of calmodulin activity, on histamine release from isolated rat mast cells.

Investigations of calmodulin involvement in cell responses has been complicated by the lack of selective calmodulin antagonists. A novel inhibitor, CGS 9343B, reportedly without influence on protein kinase C, is used in the present study of mast cell responses. The histamine release induced by antigen and compound 48/80 in the presence of calcium was enhanced by 10-20 microM CGS 9343B and inhibited by higher concentrations. Only inhibitory effects on the response to compound 48/80 in the absence of calcium and to the ionophore A23187 were observed, the latter being inhibited by 20 microM CGS 9343B. The influence on responses to combinations of the phorbol ester TPA and the ionophore A23187 was more complex, giving rise to enhancement at lower and inhibition at higher concentrations of CGS 9343B in a manner which depended on the experimental conditions. Unlike previously used calmodulin antagonists, CGS 9343B is devoid of detergent effects and without serious metabolic interference. The inhibitor seems useful to reveal differences in the mechanisms involved in responses to various histamine liberators. Our results conform with an inhibition of calmodulin by CGS 9343B but are at present inconclusive.