Cytochemical investigation into the Ca-dependence of positive and negative hormonal imprinting in Tetrahymena

Summary Insulin gives rise to positive imprinting in Tetrahymena pyriformis, but to negative imprinting in T. thermophila, as revealed by the respective increases and decreases in the insulin-binding capacity of these organisms observed during later interactions with this hormone. We found that changes in insulin-binding capacity exhibited parallelism with fluctuations of the levels of free, intracellular Ca²⁺ detectable by Quin-2 labeling. An exception was the second interaction of T. thermophila with insulin, which although showing a positive trend, produced a relatively small increase in the level of intracellular Ca²⁺. These observations suggest an interrelationship between hormone-binding capacity and the fluctuation of intracellular Ca²⁺ levels. Either hormone binding depends on the availability of Ca²⁺, or, alternatively, the latter depends on the binding capacity. Further studies are required to elucidate the true nature of this interdependence.