Distribution of IRAG and cGKI-isoforms in murine tissues.

cGMP kinase I (cGKI) signaling modulates multiple physiological processes including smooth muscle relaxation. The expression of cGKI and its substrate IRAG (Inositol 1,4,5-trisphosphate receptor associated cGMP kinase substrate) was studied. IRAG and cGKI were colocalized in the smooth muscle of aorta and colon. IRAG was present in the thalamus and in most of the myenteric plexus in the absence of cGKI. Coexpression of IRAG and cGKIbeta or cGKIalpha in COS-7 cells revealed that IRAG recruits cGKIbeta but not cGKIalpha to the endoplasmic reticulum. These results suggest that IRAG may be involved in cGKI-dependent and -independent pathways

IRAG is essential for relaxation of receptor-triggered smooth muscle contraction by cGMP kinase.

Signalling by cGMP-dependent protein kinase type I (cGKI) relaxes various smooth muscles modulating thereby vascular tone and gastrointestinal motility. cGKI-dependent relaxation is possibly mediated by phosphorylation of the inositol 1,4,5-trisphosphate receptor I (IP(3)RI)-associated protein (IRAG), which decreases hormone-induced IP(3)-dependent Ca(2+) release. We show now that the targeted deletion of exon 12 of IRAG coding for the N-terminus of the coiled-coil domain disrupted in vivo the IRAG-IP(3)RI interaction and resulted in hypomorphic IRAG(Delta12/Delta12) mice. These mice had a dilated gastrointestinal tract and a disturbed gastrointestinal motility. Carbachol- and phenylephrine-contracted smooth muscle strips from colon and aorta, respectively, of IRAG(Delta12/Delta12) mice were not relaxed by cGMP, while cAMP-mediated relaxation was unperturbed. Norepinephrine-induced increases in [Ca(2+)](i) were not decreased by cGMP in aortic smooth muscle cells from IRAG(Delta12/Delta12) mice. In contrast, cGMP-induced relaxation of potassium-induced smooth muscle contraction was not abolished in IRAG(Delta12/Delta12) mice. We conclude that cGMP-dependent relaxation of hormone receptor-triggered smooth muscle contraction essentially depends on the interaction of cGKI-IRAG with IP(3)RI

Interstitial cells of Cajal integrate excitatory and inhibitory neurotransmission with intestinal slow-wave activity.

The enteric nervous system contains excitatory and inhibitory neurons, which control contraction and relaxation of smooth muscle cells as well as gastrointestinal motor activity. Little is known about the exact cellular mechanisms of neuronal signal transduction to smooth muscle cells in the gut. Here we generate a c-Kit(CreERT2) knock-in allele to target a distinct population of pacemaker cells called interstitial cells of Cajal. By genetic loss-of-function studies, we show that interstitial cells of Cajal, which generate spontaneous electrical slow waves and thus rhythmic contractions of the smooth musculature, are essential for transmission of signals from enteric neurons to gastrointestinal smooth muscle cells. Interstitial cells of Cajal, therefore, integrate excitatory and inhibitory neurotransmission with slow-wave activity to orchestrate peristaltic motor activity of the gut. Impairment of the function of interstitial cells of Cajal causes severe gastrointestinal motor disorders. The results of our study show at the genetic level that these disorders are not only due to loss of slow-wave activity but also due to disturbed neurotransmission.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe