Although many studies show that thromboxane A(2) (TXA(2)) has the action of gastrointestinal (GI) motility using GI muscle cells and tissue, there are no reports on the effects of TXA(2) on interstitial cells of Cajal (ICC) that function as pacemaker cells in GI tract. So, we studied the modulation of pacemaker activities by TXA(2) in ICC with whole cell patch-clamp technique. Externally applied TXA(2) (5microM) produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The tonic inward currents by TXA(2) were inhibited by intracellular application of GDP-beta-S. The pretreatment of ICC with Ca(2+) free solution and thapsigargin, a Ca(2+)-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the TXA(2)-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the TXA(2)-induced effects on pacemaker currents. These results suggest that TXA(2) can regulate intestinal motility through the modulation of ICC pacemaker activities. This modulation of pacemaker activities by TXA(2) may occur by the activation of G protein and PKC independent pathway via extra and intracellular Ca(2+) modulation.
Keywords: Interstitial cells of Cajal (ICC); Intestinal motility; Pacemaker currents; Thromboxane A2 (TXA2).