Calcium oscillation linked to pacemaking of interstitial cells of Cajal - Requirement of calcium influx and localization of TRP4 in caveolae

Interstitial cells of Cajal (ICC) are considered to be pacemaker cells in gastrointestinal tracts. ICC generate electrical rhythmicity (dihydropyridine-insensitive) as slow waves and drive spontaneous contraction of smooth muscles. Although cytosolic Ca2+ has been assumed to play a key role in pacemaking, Ca2+ movements in ICC have not yet been examined in detail. In the present study, using cultured cell clusters isolated from mouse small intestine, we demonstrated Ca2+ oscillations in ICC. Fluo-4 was loaded to the cell cluster, the relative amount of cytosolic Ca2+ was recorded, and ICC were identified by e-Kit immunoreactivity. We specifically detected Ca2+ oscillation in ICC in the presence of dihydropyridine, which abolishes Ca2+ oscillation in smooth muscles. The oscillation was coupled to the electrical activity corresponding to slow waves, and it depended on Ca2+ influx through a non-selective cation channel, which was SK&F 96365-sensitive and store-operated. We further demonstrated the presence of transient receptor potential-like channel 4 (TRP4) in caveolae of ICC. Taken together, the results infer that the Ca2+ oscillation in ICC is intimately linked to the pacemaker function and depends on Ca2+ influx mediated by TRP4.