Activating of ATP-Dependent K+ Channels Comprised of Kir 6.2 and SUR 2B by PGE2 Through EP2 Receptor in Cultured Interstitial Cells of Cajal from Murine Small Intestine

Abstract

The interstitial cells of Cajal (ICC) are pacemaker cells in gastrointestinal tract and generate an electrical rhythm in gastrointestinal muscles. We investigated the possibility that PGE₂ might affect the electrical properties of cultured ICC by activating ATPdependent K⁺ channels and, the EP receptor subtypes and the subunits of ATP-dependent K⁺ channels involved in these activities were identified. In addition, the regulation of intracellular Ca²⁺ ([Ca²⁺]i) mobilization may be involved the action of PGE₂ on ICC. Treatments of ICC with PGE₂ inhibited electrical pacemaker activities in the same manner as pinacidil, an ATPdependent K⁺ channel opener and PGE₂ had only a dose-dependent effect. Using RT-PCR technique, we found that ATP-dependent K⁺ channels exist in ICC and that these are composed of K_ir 6.2 and SUR 2B subunits. To characterize the specific membrane EP receptor subtypes in ICC, EP receptor agonists and RT-PCR were used: Butaprost (an EP₂ receptor agonist) showed the actions on pacemaker currents in the same manner as PGE₂. However sulprostone (a mixed EP₁ and EP₃ agonist) had no effects. In addition, RT-PCR results indicated the presence of the EP₂ receptor in ICC. To investigate cAMP involvement in the effects of PGE₂ on ICCs, SQ-22536 (an inhibitor of adenylate cyclase) and cAMP assays were used. SQ-22536 did not affect the effect of PGE₂ on pacemaker currents, and PGE₂ did not stimulate cAMP production. Also, we found PGE₂ inhibited the spontaneous [Ca²⁺]i oscillations in cultured ICC. These observations indicate that PGE₂ alters pacemaker currents by activating the ATP-dependent K⁺ channels comprised of K_ir 6.2-SUR 2B in ICC and this action of PGE₂ are through EP₂ receptor subtype and also the activation of ATP-dependent K⁺ channels involves intracellular Ca²⁺ mobilization.