Platelet membrane-actin interaction

In order to investigate how human platelet membranes associate with cytoskeletal proteins, purified membranes were extracted with 0.6 M KI (potassium iodide) followed by extraction with 1% octyl glucoside. The depleted membranes contain a significant amount of actin (5% of the actin that was originally present in the purified membranes) which is resistant to extraction by 0.6 M KI. We have examined how this actin interacts with the membrane skeletal fraction and find that the actin is not associated with the membrane directly or indirectly through any of the major transmembrane glycoproteins (GpIb, GpIIb, and GpIIIa), or any known specific linker proteins such as actin binding protein (ABP), alpha-actinin, or spectrin. The results of an analysis of the membrane skeletal preparation using nonreducing sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) does indicate, however, that the actin, along with other proteins, exists in the form of two high molecular weight complexes. We have examined the effect of potassium iodide-octyl glucoside (KI-OG) extracted membranes upon (1) the polymerization of rabbit muscle G-actin, and (2) the actin activated Mg(2+)-dependent ATPase activity of rat skeletal muscle myosin. Based on the results of these experiments we have concluded that the actin is available for interaction with exogenously added proteins and that it might possibly be in a filamentous form. These results are compelling considering the role that the cytoskeleton is thought to play in the physiological functioning of the platelet.