Summary
In this study we investigated human blood platelet vinculin microheterogeneity, the
subcellular localization and phosphorylation of the different isoforrns before and
after platelet stimulation. At least 5 vinculin isoforms could be detected, as well
as metavinculin. These isofonns did not demonstrate a specific subcellular localization,
i. e. their relative content was similar in cytoskeleton, membrane skeleton and cytosol.
Upon platelet stimulation with thrombin a small increase in α’-vinculin was noted
in all platelet subfractions. The cytoskeleton of non-stimulated platelets contained
a minor quantity of vinculin. Upon thrombin stimulation of the platelets the cytoskeletal
vinculin content increased significantly; previously we already reported a maximal
n% incorporation of the total platelet vinculin content into the cytoskeleton upon
stimulation. A phosphorylation of a minor vinculin-isoforrl, i. e. at the α’/α location
was mainly detected in the cytoskeleton. This phosphorylation was observable in the
non-stimulated platelet cytoskeletal vinculin. These findings argue against a regulatory
role for vinculin phosphorylation in the uptake of the main isoforms of this protein
in the platelet cytoskeleton upon thrombin stimulation. The function of the phosphorylated
cytoskeletal vinculin remains to be established.
