A quantitative method for studying platelet adhesion to collagen.

A simple turbidimetric method is described that permits quantitation of both the number and the rate at which human fixed washed platelets adhere to fibrillar collagen in suspension. Fixed washed platelets were mixed with buffer or test sample in an aggregometer cuvette. Collagen was added, and the change in light transmission was recorded at 37 degrees C. Percent adhesion was obtained from the maximum change in light transmission within 5 minutes, and the adhesion rate was calculated from the initial slope of the adhesion curve. In this system, the percent adhesion was optimal at ionic strengths of 0.1 to 0.15 in a pH range of 7.0 to 8.0. Percent adhesion could be increased either by lowering the platelet number or by increasing the collagen concentration. No adherence of fixed washed platelets to heat-denatured collagen or Cytodex 3 beads was observed. Adhesion rate increased with greater stirring speed, but decreased with increasing concentrations of bovine serum albumin or normal human plasma, but the percent adhesion remained relatively constant. The rate of adhesion in 20% normal human plasma was greater than that in 1% to 4% bovine serum albumin buffer. This suggests that normal plasma contains some factor(s) that can overcome the inhibitory effect of protein on the rate of adhesion of fixed washed platelets to fibrillar collagen.