[Impact of shear stress on expression of platelet membrane glycoproteins]

To investigate the mechanism of activation of platelet by shear stress.

Specimens of whole blood were exposed to shear stress of different intensity (100, 150, 1,000, and 3,000 s(-1)) by modified cone-and-plate rotational viscometer. Then the platelets were stained with fluorescent antibody technique by flow cytometry to examine the levels of four kinds of platelet membrane glycoproteins: PAC-1, CD62P, GPIb/IX, and GPIIb/IIIa.

The expression of PAC-1 and CD62P on the surface of unactivated platelets was very low, with the rates of 1.7% +/- 1.1% (n = 5) and 0.9% +/- 0.5% (n = 5) respectively. When the platelets were exposed to high shear stress, the expression of these two kinds of glycoproteins increased. The level of PAC-1 increased quickly and obviously in a short time, reached the peak value, 73.6% +/- 7.4%, in half a minute after exposure to the shear stress of 3,000 s(-1) and decreased soon. The expression rate of CD62P was low when the platelets were exposed to low shear stress, and then increased slowly along with the increase of shear stress. After exposure to the shear stress of 3,000 s(-1) for 7 minutes, the expression rate of CD62P reached 26.4% +/- 3.5%. GPIb/IX and GPIIb/IIIa were found to exist on the surface of more than 96.5% - 99.4% of unactivated platelets. No significant change of GPIb/IX expression was found at relatively low shear stress. When the shear stress increased, the expression rate of GPIb/IX increased to an extent in 1 minute, then decreased continually. The fluorescent intensity of GPIb/IX was 72.4 +/- 6.7 while unactivated, and decreased to 44.9 +/- 4.9 (n = 5) after exposure to the shear stress of 3,000 s(-1) for 7 minutes. The expression of GPIIb/IIIa on surface of unactivated platelets, with fluorescent intensity of 98.5 +/- 12.1, began to increase under low intensity of shear stress. When the stress increased, GPIIb/IIIa expression increased quickly in a short time, and began to decrease in 7 minutes with the fluorescent intensity of 159.5 +/- 23.6 (n = 5) by then.

High shear stress causes change of expression of platelet membrane glycoproteins. Platelets are activated by high shear stress directly and independently, and the activation may be mediated by these glycoproteins.