Role of calcium and cyclic AMP on the activation of lymphocyte glycogen phosphorylase by mitogens

1. Various mitogens such as concanavalin A, phytohaemagglutinin, the pokeweed mitogen and trypsin were found to produce a rapid and transient activation of glycogen phosphorylase activity of lymphocytes incubated in a Krebs-Ringer-bicarbonate-glucose buffer. 2. Activation of the enzyme by these mitogens was always accompanied by an increase in the intracellular cyclic AMP concentration. 3. The presence of calcium ions in the incubation buffer was essential for obtaining the mitogen effects. Addition of ionophore A-23187 also produced an activation of glycogen phosphorylase, similar to that found in mitogen activation but without increase in intracellular cyclic AMP concentration. Dibutyril cyclic AMP also produced lymphocyte phosphorylase activation, even in the absence of extracellular calcium ions. 4. It is proposed that phosphorylase activation by mitogens occurs through a mechanism that involves the participation of both calcium ions and cyclic AMP.