ATP-Mn2+ stimulates the generation of a putative mediator of insulin action

Substantial evidence suggests that insulin receptor-associated protein kinase may play a pivotal role in the expression of the intracellular effects of insulin. This study was undertaken to determine whether insulin receptor kinase contributes to the generation of putative insulin mediators. The effect of ATP and divalent cation addition on the production of insulin mediators from liver plasma membranes was investigated. ATP (1 mM) added to liver plasma membranes in the absence of divalent cations enhanced insulin-stimulated release/generation of mediator slightly (approximately 3-fold). ATP in the presence of Mn2+ further increased release/generation of mediator markedly (approximately 100-fold). In contrast, ATP in the presence of Mg2+ had no stimulatory effect. Mn2+ and Mg2+ alone were ineffective. Addition of EDTA completely diminished the stimulatory effects of insulin, ATP, and Mn2+. The stimulation was ATP-specific since other nucleotides and nonhydrolyzable analogues of ATP had no or very weak activity. ATP-Mn2+ stimulated insulin-dependent mediator release/generation in a dose-dependent manner. These results suggest that insulin mediator release/generation is markedly stimulated by an ATP-Mn2+-dependent phosphorylation reaction, similar to insulin-stimulated receptor tyrosine kinase phosphorylation.