IIb Group Metal Ions (Zn2+, Cd2+, Hg2+) Stimulate Glucose Transport Activity by Post-insulin Receptor Kinase Mechanism in Rat Adipocytes

Zn2+ (1 mM), Cd2+ (1 mM), and Hg2+ (0.1 mM) belonging to the IIb group in the periodic table stimulated glucose transport activity and cAMP phosphodiesterase in rat adipocytes. The stimulation of glucose transport was due to the translocation of glucose transporters from the intracellular site to the plasma membrane. However, in intact adipocytes none of these ions stimulated insulin receptor kinase activity or phosphorylation of the 95-kDa subunit of insulin receptor or 170- or 60-kDa proteins at the tyrosyl residues. These proteins were markedly phosphorylated by addition of 0.3 nM insulin which stimulated glucose transport activity as effectively as these metal ions. These results indicate that Zn2+, Cd2+, and Hg2+ mimic insulin action by a post-receptor/kinase mechanism.