K-channel blocking drugs induce histamine release and 45Ca uptake in isolated mast cells

Histamine secretion and 45Ca uptake processes were studied in mast cells treated with four K+ channel blocking drugs in physiological saline and in media containing different ionic concentrations. Quinine, 4-aminopyridine and sparteine were effective as histamine-releasing agents when mast cells were incubated in physiologic saline solution. The dose-response profile obtained was in the range of 0.1-0.5 mM for quinine, 1-10 for 4-aminopyridine and 0.5-5 mM for sparteine and did not show significant differences between purified and unpurified mast cells. By contrast, tetraethylammonium (1-100 mM) did not induce histamine release. The presence of high K+ or Rb+ concentrations in the medium (Tris-K+ or Tris-Rb+, both at 150 mM) displaced the profile obtained to the right in cells stimulated with 4-aminopyridine or sparteine, but abolished histamine release induced by quinine. Additionally, all three K+ channel blockers increased 45Ca uptake in mast cells. The exact mechanism of the action of K+ channel blockers on mast cells is unknown. However, the fact that the drugs used were effective as histamine-releasing and 45Ca uptake promoters suggests both that mast cells might be endowed with a K+ channel activity and that the blockade of this should open certain calcium channels, leading to elevated intracellular Ca2+ levels which in turn activate mast cell secretion.