alpha-granule secretion from alpha-toxin permeabilized, MgATP-exposed platelets is induced independently by H+ and Ca2+

In order to better understand granule release from platelets, we developed an alpha-toxin permeabilized platelet model to study alpha-granule secretio n. Secretion of alpha-granules was analyzed by flow cytometry using P-selec tin as a marker for alpha-granule release. P-selectin surface expression oc curred when platelets were permeabilized in the presence of Ca2+. Responsiv eness to Ca2+ was lost 30 min after permeabilization but could be reconstit uted with MgATP. alpha-toxin-permeabilized, MgATP-exposed platelets also de granulated within a pH range of 5.4-5.9 without exposure to and independent of Ca2+. ATP, CTP, CTP, UTP, and ITP supported Ca2+-induced alpha-granule secretion, while H+-induced alpha-granule secretion occurred only with ATP and CTP. Both Ca2+- and H+-induced alpha-granule secretion required ATP hyd rolysis. Kinase inhibitors blocked both Ca2+- and H+-induced secretion. The se data suggest that alpha-granule secretion in this permeabilized platelet system shares many characteristics with granule secretion studied in other permeabilized cell models. Furthermore, these results show that H+ can tri gger alpha-granule release independent of Ca2+. J. Cell. Physiol. 179:1-10, 1999. (C) 1999 Wiley-Liss, Inc.