The response of human platelets to hypotonic stress: direct measurement of volume change.

Human platelets stored at 22 degrees C were subjected to standard hypotonic stress at intervals up to five days after collection. Changes in light absorbance were recorded during the reaction, and size distribution was measured directly using a Coulter Model ZBI Counter and Channelyzer. Recovery following osmotic stress was measured by change in absorbance, as well as by change in platelet size distribution. Significant correlation was demonstrated between the two methods. By both measures, fresh platelets demonstrated substantial recovery following hypotonic stress, but platelets stored for five days had lost this ability. The requirements for intact sulphydryl groups and the lack of effect of colchicine were confirmed.