Comparison of the insulin binding, uptake and endogenous insulin content in long- and short-term starvation in Tetrahymena.

FITC-insulin binding and endogenous insulin content of Tetrahymena pyriformis, that had been 24 h or 30 min starved, continuously fed or re-fed after starvation was studied by flow cytometry and confocal microscopy. Long starvation elevated both insulin binding and endogenous insulin content of the cells. Short re-feeding after long starvation or short starvation after continuous feeding does not change the situation. Fixed cells also bind FITC-insulin, however, in this case long starvation reduces, and re-feeding after long starvation elevates, the binding, which means that hormone binding by receptors only differs from receptor binding and engulfment (in living cells). The increase of FITC-insulin content in living cells seems to be due to engulfment, rather than by receptor binding. The results point to the unicellular organism's requirement for insulin production and binding in a life-threatening stress situation.