Effect of starvation on insulin production and insulin binding in Tetrahymena

Tetrahymena pyriformis GL was starved for 24 h and then the immunologically demonstrable insulin content and FITC-insulin binding were measured by flow cytometry and localization was studied by confocal microscopy. The amount of endogeneous insulin as well as FITC insulin binding, was highly significantly elevated. Glucose feeding for 30 min abolished the elevation of FITC-insulin binding. In starved cells, insulin-binding sites disappeared from the surface and FITC-insulin was bound inside the cells, within large food vacuoles. Endogeneous insulin was dispersed in the cytoplasm both in the control and starved cells and food vacuoles did not contain it. The results call attention to the stimulatory effect of starvation on insulin production in Tetrahymena, in parallel with the internal storage of insulin receptors, which points to an autocrine mechanism.