Role of PI3‐kinase in the development of interstitial cells and pacemaking in murine gastrointestinal smooth muscle

Abstract

Development of the pacemaker system in the small intestine depends upon signalling via tyrosine kinase (Kit) receptors. The downstream pathways initiated by Kit in interstitial cells of Cajal (ICC) have not been investigated. Wortmannin and 2‐(4‐morpholinyl)‐8‐phenyl‐4H‐1‐benzopyran‐4‐one (LY 294002), 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. ICC and electrical slow waves were present in the murine jejunum at birth. ICC and electrical rhythmicity continued to develop in neonates such that adult activity was recorded after 1 week. Development of ICC and rhythmicity were maintained in organ culture. Wortmannin or LY 294002 inhibited the development of slow waves and blocked rhythmicity within 2‐4 days. Loss of slow waves was preceded by disappearance of Kit‐positive cells from the myenteric (IC‐MY) and deep muscular plexus (IC‐DMP) regions. Wortmannin or LY 294002 had no acute effect on slow waves. Muscles from older animals (day 10‐day 30) developed resistance to wortmannin treatment, but when the exposure to wortmannin was increased to 35 days, damage to ICC networks and electrical dysrhythmias were observed. PI3‐kinase appears to be a critical downstream signalling element linking Kit receptors to ICC development and maintenance of phenotype. ICC are more 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 could result in disruption of ICC and gastrointestinal dysrhythmias.

Kit signaling is essential for development and maintenance of interstitial cells of Cajal and electrical rhythmicity in the embryonic gastrointestinal tract

“…These data demonstrate the extensive plasticity of ICC in the gastrointestinal tract. We have previously shown that Kit neutralization can inhibit pacemaker activity in jejunal tissues from P10 animals, but the time required to block slow waves (35 days) was much longer than that required to block activity in P0 muscles (the present study), suggesting the sensitivity of ICC to signaling via the Kit receptor varies as a function of the developmental period of the animal (Ward et al,1999).…”

Vagal inhibition in the antral region of guinea pig stomach

“…Intestinal preparations taken from mutant mice that lack myenteric ICC failed to generate slow waves, although they can generate action potentials (20,35). Similar findings were obtained from preparations in which the development of ICC was impaired with an antibody to c-kit, a component of ICC (25,34,37).…”

Plasticity of Interstitial Cells of Cajal: A Study in the Small Intestine of Adult Guinea Pigs

“…Similar results were reported previously that the signal pathway was essential for development of the ICCs during the fetal and neonatal periods (Maeda et al,1992; Kluppel et al,1998). In vitro study also showed that blockade of Kit or its downstream, PI3‐kinase, led to a reduction of ICCs in the bowel organ cultures from the adult mice (Ward et al,1999).…”