Role of PI3-kinase in the development of interstitial cells and pacemakingin murine gastrointestinal smooth muscle

1. Development of the pacemaker system in the small intestine depends upon signalling via tyrosine kinase (Kit) receptors. The downstream pathways ini tiated by Kit in interstitial cells of Cajal (ICC) have not been investigat ed. Wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294 002), inhibitors of phosphatidylinositol 3'-kinase (PI3-kinase), were used to test the involvement of this pathway in the development and maintenance of ICC and electrical rhythmicity in the murine small intestine. 2. ICC and electrical slow waves were present in the murine jejunum at birt h. ICC and electrical rhythmicity continued to develop in neonates such tha t adult activity was recorded after 1 week. Development of ICC and rhythmic ity were maintained in organ culture. 3. Wortmannin or LY294002 inhibited the development of slow waves and block ed rhythmicity within 2-4 days. Loss of slow waves was preceded by disappea rance of Kit-positive cells from the myenteric (IC-MY) and deep muscular pl exus (IC-DMP) regions. Wortmannin or LY 294002 had no acute effect on slow waves. 4. Muscles from older animals (day 10-day 30) developed resistance to wortm annin treatment, but when the exposure to wortmannin was increased to 35 da ys, damage to ICC networks and electrical dysrhythmias were observed. 5. PIS-kinase appears to be a critical downstream signalling element linkin g Kit receptors to ICC development and maintenance of phenotype. ICC are mo re sensitive to Kit or PI3-kinase blockade at birth, but the importance of the PI3-kinase signalling in the maintenance of ICC persists into adulthood . Interference with PI3-kinase signalling in immature or adult animals coul d result in disruption of ICC and gastrointestinal dysrhythmias.