Figure 6.

A model depicting initiation of erection by nNOS and its maintenance by eNOS. Initial stimuli from higher neural centers elicit a relatively short-lived burst of NO from nerve fibers throughout the penile tissue that relaxes smooth muscle, enhancing blood flow. PI3-kinase/Akt activation by the resulting shear stress phosphorylates eNOS (indicated with P) in endothelial cells and provides a sustained increase in NO leading to maximal relaxation that does not require continuous neuronal depolarization. CaM, calmodulin.