Kinetic modeling of blood platelet shape changes.

A prior analysis of turbidimetric data3 in terms of the specific physical and kinetic laws that describe this model led to the conclusion that the rate constants were identical. Such behavior is characteristic of a stochastic (Poisson) process, and if true, may imply the existence of a rate-limiting step common to both “sphering” (formally the A -‘ B reaction) and to the extension of long, filiform pseudopods at the expense of a concomitant decrease in body volume (formally the B -‘ C reaction). Supposedly applying the same ABC model to ADP-induced changes in right-angle light scattering by platelet suspensions, Hantgan, on the other hand, concluded that the two rate constants were different and therefore that the mechanism was not the same as previously suggested. This conclusion and others that follow from it appear to be based on a misconception as to what constitutes the ABC model, as follows. According to the model, the intensity 1(0,1) scattered at angle 0 and time I by a mixture of three morphobogically distinct platelet forms A, B, and C is given by the sum of the products of their individual scattered intensities a(0), b(0), and c(0), and their respective time-dependent concentrations A(t), B(t) and C(t) (Equation 1):