Development and persistence of receptor 'memory' in a unicellular model system.

A single exposure of Tetrahymena to diiodotyrosine stimulated replication of the unicellular organism significantly relative to the control. The stimulatory effect tended to decrease with progressing time, but was still demonstrable after as many as 500 generations. Reexposures to diiodotyrosine also enhanced cell growth, indicating the existence of a receptor 'memory' in respect to the initial exposure, but their effect tended to decline soon after initial stimulation, and did not, in all probability, contribute to the preservation of the 'memory' which itself tends to vanish gradually in due course.