Mechanism of bradykinin-induced histamine release from rat peritoneal mast cells

Bradykinin at concentrations higher than 2 μM caused a significant histamine release from rat peritoneal mast cells when extracellular Ca²⁺ was removed from the medium. Under the same experimental conditions, bradykinin increased Ca²⁺ release from the intracellular Ca store of the rat peritoneal mast cells, and a clear relationship was observed between the magnitude of histamine release and an increase in fluorescence intensity. Addition of Ca²⁺ to the medium resulted in an inhibition of the response to bradykinin in a concentration-dependent manner. Almost the same results were obtained when Mg²⁺, Ba²⁺ and La³⁺ were added to the medium. Neither B₁ nor B₂ antagonists caused significant antagonistic effects on histamine release induced by bradykinin. However, B₂ antagonists caused a histamine release of the same potency as bradykinin when applied alone. These results indicate that bradykinin-induced histamine release is not attributable to a bradykinin receptor.