INHIBITION BY CROMOGLYCATE AND SOME FLAVONOIDS OF NUCLEOSIDE DIPHOSPHATE KINASE AND OF EXOCYTOSIS FROM PERMEABILIZED MAST-CELLS

1 The anti-allergic compound, cromoglycate, is reported to possess aff inity for, and to suppress the autophosphorylation of a 72kDa protein having the sequence of nucleoside diphosphate kinase (NDPK). 2 We have tested the ability of cromoglycate, and a panel of ten structurally r elated flavonoids of plant origin, to inhibit the NDPK reaction and th e exocytotic process of permeabilized mast cells. The conditions of pe rmeabilization (use of an isotonic medium based on sodium glutamate) w ere selected to ensure that NDPK activity would be an essential compon ent in the induction of Ca2+-induced exocytosis in which ATP is requir ed for generation of GTP. For comparison, we also measured the inhibit ion of exocytosis induced by GTP-gamma-S; this proceeds in the absence of ATP and bypasses the need for NDPK activity. 3 We found that cromo glycate does not discriminate between Ca2+ and GTP-gamma-S-induced exo cytosis and is a poor inhibitor of NDPK activity. Concentrations in th e millimolar range are required for inhibition of all these functions. By comparison, many of the flavonoids are effective at concentrations in the micromolar range. 4 While we were unable to discern any system atic relationships between their ability to inhibit the three function s, two compounds, quercetin and genistein, inhibit Ca2+-induced, but n ot GTP-gamma-S-induced exocytosis. Inhibition of the late stages of th e stimulus-response pathway in mast cells by these compounds is theref ore likely to be due to inhibition of NDPK and the consequent failure to generate GTP.