Calcium Uptake and Collagen‐Induced Platelet Release Reaction

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Abstract
Platelet aggregation induced by collagen is Ca dependent and involves a release of adenine nucleotides, 5‐hydroxytryptamine, and other compounds stored in granules within the platelets. In purely secretory systems such as the adrenal medulla, uptake of Ca is a necessary step in the release reaction. The purpose of the present investigation was therefore to establish to what extent an uptake of Ca also plays an important role in the platelet release reaction. It was found that guanethidine, which is reported to inhibit Ca‐uptake in concentrations from 10‐6 to 10‐4 M, and BaCl2 (10‐3 M) did not significantly influence the aggregation response. In a second series of experiments the uptake of 45Ca during aggregation was determined. No difference in uptake was observed between these experiments and experiments in which no aggregation was induced. The results do not indicate that uptake of Ca is a necessary step in the collagen induced platelet release reaction.