HISTAMINE-RELEASE BY EXOCYTOSIS FROM RAT MAST-CELLS ON REDUCTION OF EXTRACELLULAR SODIUM - SECRETORY RESPONSE INHIBITED BY CALCIUM, STRONTIUM, BARIUM, OR MAGNESIUM

Histamine release from peritoneal mast cells of the rat was stimulated when the cells were exposed for 10 min to Na deficient media where all NaCl was replaced by KCl, RbCl, glucose, sucrose, mannitol, or Tris, provided Ca was less than about 0.5 mM. Light and EM showed the response to be exocytosis. The chelating agents, EDTA and EGTA [ethylene glycol bis(.beta.-aminoethyl)ether N,N, N'',N''-tetraacetic acid], abolished the response to Na lack and their inhibitory effects were reversed by re-incubating cells with Ca but not Mg. The response was inhibited by dinitrophenol combined with glucose-deprivation. The response was inversely related to the concentrations of Na and Ca below 137.5 and 0.5 mM, respectively. The related alkaline earth metals, Ba, Sr and Mg, resembled Ca in inhibiting the response to Na lack. No secretory response was seen when the cells were exposed for 10 min to Ca-free medium in which Li replaced Na. Exposure to this medium for 60 min elicited secretion. When extracellular Ca is low, a reduction in extracellular Na apparently induces a conventional exocytotic secretory response dependent on energy and cellular Ca. Na lack may mobilize Ca from a cellular site, possibly the inner aspect of the plasma membrane.