Mode of insulin action.

A unifying hypothesis is proposed for the mechanism of insulin action in adipose tissue. Insulin both induces displacement of Ca++ from a membrane-bound pool and inhibits efflux of the ion, thereby facilitating a rise in intracellular free Ca++ concentration. The former effect could enhance the transport of substrates and ions into the cell, while the latter modulates the activity of some intracellular enzymes to stimulate glycogenesis, lipogenesis, and decrease lipolysis and glycogenolysis. The calcium ion might act as the missing second messenger for insulin action.