BINDING AND METABOLISM OF PLATELET-ACTIVATING-FACTOR (PAF) BY ISOLATED RAT TYPE-II PNEUMONOCYTES

The specific binding of platelet-activating factor (PAF) to isolated t ype II pneumonocytes from rat lung has been investigated employing an intact cell preparation. The dissociation constant (K-d) for the autac oid has been determined to be 0.46 X 10(-9) M and approximately 3000 r eceptor sites per cell are present. In studies conducted on the metabo lism of PAF in these cells, it was demonstrated that PAF is rapidly co nverted into 1-alkyl-2-acylglycerophosphocholine (alkyl-acyl GPC). Aft er longer time intervals there was a substantial conversion of alkyl-a cyl GPC into alkyl-acylglycerophosphoethanolamine (allkyl-acyl GPE). B oth the alkyl-acyl GPC and alkyl-acyl GPE fractions were devoid of pla smalogens. The alkyl-acyl GPC fraction was further characterized and a distinct double peak could be visualized following thin-layer chromat ography and the same lyso-compound was produced from both peaks follow ing mild. alkaline hydrolysis. By using appropriate standards it was c oncluded that the dual alkyl-acyl GPC peaks represent differences in t he fatty acid present in the sn-2 position. One peak corresponds to th e presence of saturated fatty acid in the sn-2 position and is probabl y due to the characteristic high capacity of the type II cells to prod uce disaturated glycerophospholipids. (C) 1994 Academic Press, Inc.