Micropipette aspiration of human platelets: influence of rewarming on deformability of chilled cells.

Recent studies using micropipette elastimetry have shown that the circumferential microtubule supporting the discoid form of resting platelets has a direct influence on the resistance of the cell to deformation. However, the findings did not resolve whether the mere presence of microtubules, their organization into coils, or location under the cell wall was responsible for resistance to aspiration into micropipettes. In the present study platelets were cooled to 2 degrees to 4 degrees C to remove microtubules completely. The chilled cells were then rewarmed to 37 degrees C, and the influence of microtubule reassembly on resistance to deformation in micropipettes measured at intervals up to 1 hour. Chilled platelets without microtubules were aspirated more than twice as far as control platelets at all negative pressures from 1 to 10 cm H2O (tensions 4 to 41 X 10(-2) dynes/cm). At negative tensions beyond 32.5 X 10(-2) dynes/cm (8 cm H2O), the aspirated lengths of control platelets plateaued until the cells finally fragmented. Aspirated segments of chilled platelets continued to increase in length on exposure to greater negative pressure. Twenty minutes after rewarming at 37 degrees C, chilled cells began to return toward normal resistance to aspiration when only 6% had recovered discoid shape. The range of deformability at this time was narrow, indicating that partial recovery was not caused by development of two cell populations, one with and one without microtubules. The return toward normal resistance continued at 30 minutes when 75% of platelets were discoid, and was identical to that in control platelets after 1 hour at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)