Lateral mobility of integrin alpha IIb beta 3 (glycoprotein IIb/IIIa) in the plasma membrane of a human megakaryocyte.
The migration of integrins to sites of cell-cell and cell-matrix contact is thought to be important for adhesion strengthening. We studied the lateral diffusion of integrin alpha IIb beta 3 (glycoprotein IIb/IIIa) in the plasma membrane of a cultured human megakaryocyte by fluorescence recovery after photobleaching of FITC-labelled monovalent Fab fragments directed against the beta 3 subunit. The diffusion of beta 3 on the unstimulated megakaryocyte showed a lateral diffusion coefficient (D) of 0.37 x 10(-9) cm2/s and a mobile fraction of about 50%. Stimulation with ADP (20 microM) or alpha-thrombin (10 U/ml) at 22 degrees C induced transient decreases in both parameters reducing D to 0.21 x 10(-9) cm2/s and the mobile fraction to about 25%. The fall in D was observed within 1 min after stimulation but the fall in mobile fraction showed a lag phase of 5 min. The lag phase was absent in the presence of Calpain I inhibitor, where-as cytochalasin D completely abolished the decreased in mobile fraction. The data are compatible with the concept that cell activation induces anchorage of 50% of the mobile alpha IIb beta 3 (25% of the whole population of receptor) to the cytoplasmic actin filaments, although, as discussed, other rationals are not ruled out.
Schootemeijer
A
A
Department of Haematology, University Hospital Utrecht, The Netherlands.
van Willigen
G
G
van der Vuurst
H
H
Tertoolen
L G
LG
De Laat
S W
SW
Akkerman
J W
JW
D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D005453:Fluorescence; D005456:Fluorescent Dyes; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism* / Q000648:ultrastructure; D010775:Photic Stimulation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*
D005456:Fluorescent Dyes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex