Possible mechanisms of the concentration-dependent action of substance P to induce histamine release from rat peritoneal mast cells and the effect of extracellular calcium on mast-cell activation.

Rat peritoneal mast cells purified on a Percoll gradient were loaded with the fluorescent Ca2+ indicator fura-2 and were challenged with different concentrations of substance P (SP), and intracellular calcium concentrations ([Ca2+]i) were measured by a spectrofluorometric assay. SP at 5 x 10(-6) mol/l and 10(-5) mol/l caused a significant histamine release with a significant increase in [Ca2+]i in a dose-dependent manner. However, SP at 10(-8)-10(-6) mol/l did not induce either histamine release or increase in [Ca2+]i. Extracellular calcium at 0.9 mM inhibited the histamine release with a significant reduction of [Ca2+]i compared with that of the cells in a nominally calcium-free condition. These results indicate that the action of SP on rat mast cells relies upon [Ca2+]i to induce histamine release.