ULTRASTRUCTURAL ALTERATIONS IN THROMBOCYTES OF THE SNAKE WAGLEROPHIS-MERREMII AFTER ACTIVATION BY ADP

The ultrastructure of the resting thrombocytes of the snake Waglerophi s merremii and the process of ADP aggregation are studied. These throm bocytes are nucleate, ellipsoidal, and contain a marginal band. Endopl asmic reticulum and ribosomes are few. An open canalicular system, Gol gi complex, granules resembling the alpha-granules in human platelets, and structures similar to secondary lysosomes are also present. The a ctivation response of W. merremii thrombocytes to ADP is examined and compared to the morphological alterations in human platelets. The thro mbocytes, normally ellipitical in shape, become spheroid with cytoplas mic protrusions, and adhere to one another. The open canalicular syste m undergoes dilation and the granules cluster at the centre of the thr ombocytes. The release reaction of these granules occurs after stimula tion by ADP, similar to what happens in human platelets. This similari ty may suggest a process of evolutional specialization since thrombocy tes in the majority of non-mammal vertebrates are not aggregated by AD P.