Transient Receptor Potential Canonical 4 and 5 Channel Antagonist ML204 Depolarized Pacemaker Potentials of Interstitial Cells of Cajal

BACKGROUND/AIMS: To investigate an effect of ML204 (an inhibitor of transient receptor potential canonical 4 and 5 [TRPC4/5] channels) on interstitial cells of Cajal (ICCs) and therefore determine whether TRPC4/5 channels act on ICC-generated pacemaker activity. METHODS: We enforced whole cell patch clamp analysis, measurements of the intracellular Ca2+ concentration, and reverse transcription polymerase chain reaction to determine the effect of ML204 (10 μM) or englerin A (a selective activator of TRPC4/5 channeles, 10 μM) and the existence of TRPC4/5 in mouse small intestinal ICC. RESULTS: Treatment of ICCs with ML204 or englerin A caused the membrane potentials to depolarize. This depolarization effect of membrane potentials by ML204 in ICCs was observed to be concentration-dependent. After treating Ca(2+)- and Na(+)-free solutions or flufenamic acid (a non-selective cation channel blocker), the pacemaker potentials in the ICCs were abolished. A specific anoctamin 1 channel blocker did not have any effect on the pacemaker activity in ML204-untreated control cells; however, they blocked ML204-induced pacemaker activity in ICCs. Specific primers designed against TRPC4 and TRPC5 detected the presence of TRPC4/5 in small intestinal ICCs, and the application of ML204 increased raise the frequency of Ca(2+) oscillations in ICCs, as assessed using Fluo-4 AM. Conclusion The results implied that ML204 could not inhibit the pacemaker activity but depolarized the membrane potential of ICCs by regulating intracellular Ca(2+) oscillations and anoctamin 1 channels.