Differential responses to prostaglandins in the circular and longitudinal muscle layers of the murine ileum

Prostaglandin E₂ (PGE₂) actions on intestinal motility are complex due to the differential expression of the PGE₂ receptors EP₁-EP₄. We sought to determine the actions of PGE₂ on electrical pacemaker and contractile activity of the circular and longitudinal muscle layers of the murine small intestine. Intracellular microelectrode and isometric force measurements were performed to examine the effects of PGE₂ receptor activation on circular and longitudinal muscle layers. In the two muscle layers, PGE₂ produced differential responses. In the circular muscle layer, PGE₂ caused dose-dependent membrane hyperpolarization and a reduction in slow-wave amplitude, accompanied by a decrease in the amplitude of phasic contractions. Membrane hyperpolarization and the reduction in slow-wave amplitude and phasic contractions were insensitive to tetrodotoxin (TTX) and <i>N</i>^ω-nitro-l-arginine (l-NNA) but inhibited by the K_ATP channel antagonist glibenclamide. The actions of PGE₂ on the circular muscle layer were mimicked by the selective EP₂ and EP₄ agonists ONO AE1-259 and ONO AE1-329, respectively. The actions of PGE₂ were partially inhibited by the EP₄ antagonist ONO AE3-208. The EP₁ agonist ONO-DI-004 produced little effect, whereas the EP3 agonist ONO-AE-248 caused dose-dependent membrane depolarization. In comparison, PGE₂ produced increased tone and phasic contractions in the longitudinal muscle layer that was mimicked by ONO-DI-004 and ONO-AE-248, whereas EP₂ and EP₄ agonists had little effect on contractile activity. These data suggest that differential expression of PGE₂ receptors on intestinal muscle layers can produce antagonistic actions on intestinal motility.<b>NEW & NOTEWORTHY</b> Prostaglandins are lipid mediators that have complex actions on gastrointestinal motility that are highly dependent on the expression of the receptor subtypes where they exert their actions. PGE₂ has inhibitory or excitatory effects on circular or longitudinal muscle layers of the small intestine. Despite many studies of the effects of prostaglandins on tissue contractility, little is known about the specific receptors eliciting these effects. The present study examines functional receptor expression in the small intestine.