Mechanism of damnacanthal-induced [Ca²⁺](i) elevation in human dermal fibroblasts

Damnacanthal is a potent and selective inhibitor of p56(lck) tyrosine kinase in a variety of tissues. We have found, however, using the Ca²⁺ microfluorimetry technique, that damnacanthal releases intracellular Ca²⁺ stores and promotes Ca²⁺ entry in human dermal fibroblasts. The effect of damnacanthal on the peak [Ca²⁺](i) values and the latent time to the peak was concentration-dependent. Damnacanthal releases Ca²⁺ from thapsigargin- sensitive Ca²⁺ stores, and the Ca²⁺ stores responding to damnacanthal were overlapped with those of bradykinin. Damnacanthal-induced Ca²⁺ entry was mediated by voltage-dependent and voltage-independent Ca²⁺ channels. This effect of damnacanthal on intracellular Ca²⁺ mobilization was also observed in cultured bovine coronary endothelial cells but not demonstrated in freshly isolated rat basilar smooth muscle cells. Our study suggests that damnacanthal increases intracellular Ca²⁺ by releasing Ca²⁺ from internal stores and promoting Ca²⁺ entry. The relationship between the actions of damnacanthal on tyrosine kinase and intracellular Ca²⁺ requires further investigation. (C) 2000 Elsevier Science B.V.