Akt phosphorylation of neuronal nitric oxide synthase regulates gastrointestinal motility in mouse ileum

Significance Neuronal nitric oxide synthase (nNOS) is believed to be activated primarily by Ca 2+ /calmodulin. Activation of nNOS by phosphorylation similar to endothelial NOS has been suggested but is technically difficult to confirm in vivo. We developed a knock-in mouse with nNOS serine1412 mutated to alanine and show using mouse ileum that nNOS phosphoserine1412 regulates gastrointestinal smooth muscle relaxation and functional motility. nNOS is phosphorylated by the protein kinase Akt during submaximal neuronal depolarization to augment NO-cGMP signaling in a manner tuned toward resting intracellular Ca 2+ levels. Phosphorylation at nNOS serine1412 represents a previously unrecognized physiologic mechanism of nNOS regulation linking neuronal depolarization to gastrointestinal motility and clarifies characteristics of neuronal NO production.