Further experiments in unicellular model system to substantiate receptor amplification.

In a previous experiment histamine, a phagocytosis promoting hormone of vertebrates, was employed to enhance the phagocytosis of Tetrahymena to demonstrate the possibility of receptor amplification by a short treatment. A long-term treatment with histamine also stimulated the phagocytotic activity of the Tetrahymena, and the stimulatory effect persisted for some time after return to plain medium. In this experiment the function was observed and the hormone binding of cells was not taken into consideration. In the present study evidence was obtained that a lasting first exposure to histamine durably enhanced the histamine binding capacity of the unicellular. This indicates a parallelism of alterations in the histamine binding capacity and phagocytotic function of Tetrahymena. It was also shown that lasting re-exposure to histamine depressed rather than enhanced the histamine binding.