A study of the kinetics of ADP-triggered platelet shape change
RR Hantgan
The rapid transformation of human blood platelets from inert discoid cells
to spheroechinocytes that is induced by adenosine diphosphate (ADP) has
been followed by right-angle light scattering intensity measurements using
a laser light source and a sensitive photomultiplier. Two steps have been
observed, and their rate constants have been determined as a function of pH
and [ADP] and in the presence and absence of calcium for both platelet-rich
plasma and gel-filtered platelets. Both steps are significantly faster in
the presence of physiologic levels of calcium. Platelets were fixed prior
to and during activation, then examined by phase-contrast and scanning
electron microscopy. The light scattering and morphological changes support
a model in which, under physiologic conditions of pH, temperature, ionic
strength, and calcium concentration, the initial rapid event in platelet
shape change is the loss of discoid shape, with a decay time of two to
three seconds, leading to an intermediate with short pseudopods. The slower
extension of long pseudopods occurs next, with a time constant of
approximately seven to eight seconds. These results may help to resolve the
contradictory descriptions of the mechanism of platelet shape change that
have recently appeared in the literature.
Volume 64,
Issue 4,
pp. 896-906,
10/01/1984
Copyright © 1984 by The American Society of Hematology
