All of the following are second messengers, EXCEPT:

The ligands in the ECF bind to receptors on the surface of cells and trigger the release of intracellular mediators such as cAMP, IP3, and DAG that initiate changes in cell function. These intracellular mediators are called "second messengers." Second messengers bring about many sho-term changes in cell function by altering enzyme function, triggering exocytosis, and so on, but they also can lead to the alteration of transcription of various genes. Guanylyl cyclases are a family of enzymes that catalyze the formation of cGMP. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 2. Overview of Cellular Physiology in Medical Physiology. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.