The influence of hypertonicity on histamine release from isolated rat mast cells

Increasing the tonicity of the incubation medium gradually inhibited histamine release from isolated rat mast cells when induced A-23187, ATP, Thapsigargin, sodium fluoride and compound 48/80 in the presence of extracellular calcium, as well as by the latter in the presence of calcium. In contrast, hypertonicity had but negligible effect on the release caused by the monovalent cation inophore X-537A. The swelling action induced by both ATP and X-537A on rat mast cells was markedly depressed by hypertonicity. Thus, the swelling action seemed to be inherent to the mechanism by which ATP stimulates mast cells to a calcium-dependent histamine secretion, whereas this was not the case with X-537A. For Thapsigargin and sodium fluoride it was demonstrated that only the secretory step, induced by calcium, was inhibited by hypertonicity, and this could be reversed by adjusting the incubation medium to isotonicity. Therefore, the results suggest that the uptake of calcium in the rat mast cells after stimulation is a passive process.