Comparison of the major membrane glycoproteins and proteins of human, rabbit and rat blood platelets

Rabbit and rat blood platelets behave differently from human platelets in response to a number of aggregating agents. The aim of this work was to compare platelet membrane glycoproteins (GP) and proteins of these 3 species and relate these results to physiological functions. Washed platelets were surface labelled by techniques specific for their oligosaccharide (sialic acid, galactose /N-acetyl galactosamine) or protein moieties, and separated on a high resolution Laemmli SDS polyacrylamide gel. Higher labelling of terminal galactose / N-acetyl galactosamine residues was obtained for rat and rabbit platelets as compared to human. Glycoproteins of rabbit and rat platelets migrating at the same position as the most sialylated human platelet GP (Ib), were insignificantly labelled. However, in rabbit and rat platelets, the most sialylated GP were located at an apparent molecular weight (Mr) similar to and above human Ia, and part of this GP was lost in the supernatant in the presence of 0.002 M Ca ++. Rat membrane proteins having a similar Mr to iodinated human platelet membrane proteins (IIb, IIIa) were weakly labelled in contrast to rabbit membrane proteins. These studies demonstrate differences between the platelet membrane protein and GP composition of rabbit, rat and human platelets, which may explain some of the differences observed in vitro with aggregation responses in these species.