Thrombin-induced degranulation of cultured bone marrow-derived mast cells: Effect on calcium uptake

The role of calcium in the mechanism of thrombin activation of bone marrow-derived mast cells (BMMC) was explored by measuring the changes in the uptake of ⁴⁵Ca²⁺ into quiescent BMMC and into cells stimulated by thrombin or by IgE-antigen. The results indicate that activation of BMMC by either thrombin or IgE-antigen is Ca²⁺-dependent. One million BMMC, activated by 0.05-5 U thrombin, accumulated ⁴⁵Ca²⁺ in a concentration-dependent manner, which levelled off at around 1 U thrombin. Extracellular ⁴⁵Ca²⁺ uptake of thrombin-stimulated cells is saturable within 90 seconds and corresponds to the kinetics of histamine release, whereas that of IgE-antigen exposed cells continues unabated for over 5 min. The pattern of ⁴⁵Ca²⁺ uptake of IgE-sensitized BMMC exposed to thrombin suggests that the prostimulatory locus of thrombin action on the surface membrane is distinct from that of IgE.