PGE<SUB>2</SUB> Regulates Pacemaker Currents through EP<SUB>2</SUB>-Receptor in Cultured Interstitial Cells of Cajal from Murine Small Intestine

PGE<SUB>2</SUB> Regulates Pacemaker Currents through EP<SUB>2</SUB>-Receptor in Cultured Interstitial Cells of Cajal from Murine Small Intestine

The interstitial cells of Cajal (ICCs) are the pacemaker cells in gastrointestinal tract and generate electrical rhythmicity in gastrointestinal muscles. Therefore, ICC may be modulated by endogenous agents such as neurotransmitter, hormones, and prostaglandins (PGs). In the present study, we investigated the effects of prostaglandins, especially PGE<SUB>2</SUB>, on pacemaker currents in cultured ICCs from murine small intestine by using whole-cell patch clamp techniques. ICCs generated spontaneous slow waves under voltage-clamp conditions and showed a mean amplitude of &#8291;452&#8273;39 pA and frequency of 18&#8273;2 cycles/min (n=6). Treatments of the cells with PGE<SUB>2</SUB> (1μM) decreased both the frequency and amplitude of the pacemaker currents and increased the resting currents in the outward direction. PGE<SUB>2</SUB> had only inhibitory effects on pacemaker currents and this inhibitory effect was dose-dependent. For characterization of specific membrane EP receptor subtypes, involved in the effects of PGE<SUB>2</SUB> on pacemaker currents in ICCs, EP receptor agonists were used: Butaprost (1μM), EP<SUB>2</SUB> receptor agonist, reduced the spontaneous inward current frequency and amplitude in cultured ICCs (n=5). However sulprostone (1μM), a mixed EP<SUB>1</SUB> and EP<SUB>3</SUB> agonist, had no effects on the frequency, amplitude and resting currents of pacemaker currents (n=5). SQ-22536 (an inhibitor of adenylate cyclase; 100μM) and ODQ (an inhibitor of guanylate cyclase; 100μM) had no effects on PGE<SUB>2</SUB> actions of pacemaker currents. These observations indicate that PGE<SUB>2</SUB> alter directly the pacemaker currents in ICCs, and that the PGE<SUB>2</SUB> receptor subtypes involved are the EP<SUB>2</SUB> receptor, independent of cyclic AMP- and GMP-dependent pathway.