Summary
We have previously suggested that the human homologue of theDrosophila transient receptor potential protein, TRPC1, is involved in conducting store-operated
Ca2+ entry (SOCE) in human platelets since an antibody raised against the poreforming
region of TRPC1 inhibited SOCE. Here we have investigated plasma membrane expression
of TRPC1 in human platelets and have probed for the presence of otherTRPC proteins
in these cells. Biotinylation revealed the presence of TRPC1 in the plasma membrane
of resting platelets. Surface expression was not detectibly changed following Ca2+ store depletion or stimulation with thrombin. Western blotting demonstrated the presence
of TRPC1, TRPC3, TRPC4, TRPC5 and TRPC6 in platelet lysates. TRPC1, TRPC4 and TRPC5
coimmunoprecipitated, as did TRPC3 and TRPC6. TRPC1, TRPC4 and TRPC5 were associated
with detergent-resistant platelet membranes, from which they were partially released
when the cells were cholesterol-depleted using methyl-β-cyclodextrin. The distributions
of TRPC3 and TRPC6 between soluble and membrane fractions were not affected by methyl-β-cyclodextrin
treatment. These results suggest that TRPC1,TRPC4 and TRPC5 form a heteromultimer
associated with platelet lipid raft domains, whereas TRPC3 and TRPC6 associate independently
of lipid rafts.
Keywords
Platelet physiology - signal transduction - thrombin