Micropipette aspiration of human platelets after exposure to aggregating agents.

The present study examined the influence of activation on platelet deformability. Aspiration of cells after exposure to thrombin, adenosine 5' -diphosphate, or the calcium ionophore A23187 at concentrations producing shape change and stickiness revealed significant changes from control cells. At the lowest negative pressure, 4 X 10(-2) dynes/cm (-1 cm H2O), there were no differences in lengths of membrane segments aspirated from control and activated platelets. Each subsequent increase in negative pressure up to 35 X 10(-2) dynes/cm (-7.5 cm H2O) resulted in significantly longer aspirated segments on activated cells compared to control cells. Greater negative pressures did not cause further increases in lengths of membrane segments drawn into the pipette. Thus, activation, which results in constriction of the circumferential microtubule, makes more membrane available for aspiration as negative pressure is increased. In both control and activated platelets, the microtubule coils served as a barrier to further lengthening of aspirated membrane segments as negative pressure was increased beyond 35 X 10(-2) dynes (-7.5 cm H2O).