Light scattering changes of edetic acid-treated, washed rat platelets: effect of adenosine diphosphate and calcium...

The effe-ts of adenosine diphosphate (ADP) and Ca2+ on platelet morphology were studied in edetic acid (EDTA)-treated, washed platelets of rat by means of light scattering measurement at right angles. ADP caused a transient change of light scattering, which was independent of concentration above 5 muM and of pH between 4 and 10. When the platelets were pretreated with ADP or chilled persistently, Ca2+ also caused another transient change of light scattering. The effect of Ca2+ was abolsihed at pH below 6.5. The velocity of both ADP- and Ca2+-induced response was dependnet on temperature, and the magnitude was reduced by metabolic inhibitors and SH-blocking agents. Adenosine triphosphate (ATP) competitively inhibited the ADP-induced response, but not the Ca2+-induced one. The response to Ca2+ of the control and chilled platelets was compared by scanning electron microgram. Apparent similarity of the effect of chilling on membrane structure to that of ADP was suggested.