A biochemical study of hydroxyapatite crystal induced enzyme release from neutrophils.

Addition of hydroxyapatite (HyAp) microcrystals to human neutrophils results in exocytosis of specific granules, measured as lysozyme release, and plasma membrane damage, evident from lactate dehydrogenase (LDH) release. The strong hydrogen acceptor polyvinylpyridine-N-oxide has no effect on enzyme release, but polyanions and negatively charged proteins such as albumin strongly inhibit HyAp induced enzyme release. HyAp crystals cause only slightly less membrane damage in neutrophil cytoplasts than in intact neutrophils. Removal of sialic acid from the cells did not affect HyAp induced enzyme release. Glucose, trapped in negatively charged liposomes, is released by HyAp crystals, whereas the crystals do not release glucose from positively charged liposomes. The results indicate that positive charges located on the HyAp crystals are of predominant importance for the effect of the crystals, and that the lipid part of the membrane might play an important part in the interaction.