The effect of thrombin on the organization of human platelet membrane glycosphingolipids. The sphingosine composition of platelet glycolipids and ceramides.

Abstract

Surface-exposed glycolipids in human platelets were investigated with nonpenetrating membrane probes, NaB3H4/galactose oxidase and NaB3H4/periodate. Trihexosylceramide, globoside, and hematoside were exposed in resting platelets. The incubation of platelets with thrombin resulted in a 50% reduction in the labeling of both trihexosylceramide and globoside and a 100% increase in labeling of hematoside on the platelet surface. The quantitation of glycolipids in platelets incubated with thrombin revealed no changes in the amounts of trihexosylceramide and globoside but there was an increase in hematoside. These experiments indicate that there is a specific rearrangement of glycolipids on the surface of thrombin-treated platelets. The study also showed that both ceramide A and B are present in platelets. The former contained 3.36 nmol of sphingosine and the latter 0.12 nmol of sphingosine/10(9) platelets. The sphingosine composition of ceramide B, glucosylceramide, and the minor platelet gangliosides was similar and they were composed of two-thirds erythrosphingosine (18:1) and one-third threosphingosine (18:1). The composition of lactosylceramide, trihexosylceramide, globoside, and hematoside was related to ceramide B and they contained about 60% erythrosphingosine (18:1), 25% threosphingosine (18:1), and 10% dihydrosphingosine (18:0). Ceramide A differed in that it was composed of 56% erythrosphingosine (18:1), 34.7% dihydrosphingosine (18:0), 4.3% threosphingosine (18:1), 2.7% erythrosphingosine (16:1), and 2.3% erythrosphingosine (17:1). The sphingosine composition of sphingomyelin resembled that of ceramide A but did not contain threosphingosine (18:1). The possibility that platelet ceramide B is involved n glycolipid metabolism and ceramide A in sphingomyelin metabolism is considered.