CALCIUM DEPENDENT SEROTONIN RELEASE FROM BLOOD-PLATELETS - MODEL SYSTEM FOR NEUROSECRETION

In contrast to most neurosecretory systems, blood platelets are capable of serotonin secretion in the absence of extracellular Ca. The agents which trigger Ca2+-independent release are also strong aggregating agents. Under conditions where platelet aggregation is minimized, a strong dependence of the release of serotonin on extracellular Ca was observed. Aggregation was controlled through the use of creatine phosphokinase, which reduces the level of extracellular ADP, and concanavalin [Con]A as secretogogue, a treatment which has minimal aggregating activity. Optimal conditions for release were 100 .mu.g/ml Con A and 1.0-5.0 mM Ca2+. Titration studies and experiments using radiolabeled Con A implied that the interaction between Ca2+ and Con A on release does not reflect altered binding of the lectin to the [rat] platelets. Ionic species which affect other Ca2+-dependent release systems had similar effects on the system described. In the absence of aggregation, blood platelets possess a release system analogous to other secretory cells. This, combined with the structural simplicity of the platelet and the homogeneity of platelet preparations, suggests that platelets warrant consideration as a model system for biochemical studies of the release process.