The regulatory role of calmodulin-dependent guanylate cyclase in association with hormonal imprinting in Tetrahymena

The primary interaction with insulin accounted for considerable increases in both the calmodulin content and guanylate cyclase activity of Tetrahymena. Both activities were still elevated after 24 h (6-8 generations), but while the calmodulin level showed a decrease, guanylate cyclase activity showed a further significant increase relative to the immediate response. A second treatment with insulin decreased rather than increased both activities, but to dissimilar degrees, in that the calmodulin content returned to the control level, whereas guanylate cyclase activity still increased over the level measured after the first treatment. It appears that insulin imprinting altered the calmodulin-dependent guanylate cyclase regulation in Tetrahymena, and caused a switch-over to an 'energy-saving' system through decelerating the breakdown of cGMP by phosphodiesterase.