Abstract
Cultured myoblasts derived from limb muscle of newborn rats express thrombin receptor immunoreactivity on their surface. Receptor expression is repressed upon myoblast fusion. This is due at least in part to a decrease in the amount of the thrombin receptor mRNA. Addition of thrombin triggers calcium transients only in mono- but not multinucleated muscle cells. Furthermore, thrombin increases the rate of myoblast proliferation that coincides with an activation of mitogen-activated protein kinase. Northern analysis of thrombin receptor mRNA expression in skeletal muscle showed that the transcript is present at a relatively high level at birth, but is almost undetectable in the adult. By in situ hybridization, the mRNA at birth appeared to be present mostly in mononucleated cells grouped in clusters, but not in muscle fibers. Very few nuclei surrounded by a mRNA signal were present on muscle sections of rats 24 days postnatally. These results suggest that the thrombin receptor plays a role in muscle development.
Highlights
Most of the cellular effects of thrombin are mediated via the thrombin receptor (ThR).1 This receptor is a member of the G protein-coupled receptor family and is activated by cleavage of an Arg–Ser bond within its N-terminal extracellular domain [1, 2]
Such conditions are known to Thrombin Receptor in Muscle induce receptor internalization [36, 37]
Myoblasts appear to fuse as ThR-expressing cells (Fig. 2, lower panel) and thereafter the receptor immunoreactivity is absent in the differentiated state
Summary
Human ␣-thrombin was a generous gift of Dr Stuart Stone, MRC Center, University of Cambridge, Cambridge, UK. Transferrin, lysophosphatidic acid, and phorbol 12-myristate 13-acetate were from Sigma
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