Subcellular localization of 1-alkyl-Sn-glycero-3-phosphocholine (LPAF) metabolites in human neutrophils (HPMN)

Cellular catabolism of platelet activating factor proceeds by hydrolysis and the subsequent highly selective incorporation of arachidonic acid. To determine the subcellular site(s) of LPAF acylation 107 HPMN were incubated with 20 nM [3H]LPAF complexed to albumin in phosphate buffered saline for 2 hrs at 370. TLC demonstrated that over 85% of incorporated radioactivity was present in choline glycerophospholipids and RPHPLC demonstrated that over 80% of radio-labeled lipids migrated as a single molecular species. Quantitative electron microscopic autoradiography was performed after tissue processing spatially fixed 86% of incorporated radioactivity. The nuclear membrane and the endoplasmic reticulum were highly labeled (70% of incorporated radioactivity). In contrast the specific activity of the HPMN granule membranes and plasma membrane were 10 and 100 fold lower, respectively. Furthermore, treatment of HPMN with 20 nM LPAF resulted in marked alterations in nuclear membrane ultrastructure including fusion, folding, and aggregation of nuclear pore complexes although the morphology of other cellular membranes was unchanged. These results demonstrate that LPAF metabolites are highly compartmentalized and suggest that internal membranes but not the plasma membrane are the critical sites of intracellular metabolism