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 Ca(2+) has been assumed to play a key role in pacemaking, Ca(2+) 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 Ca(2+) oscillations in ICC. Fluo-4 was loaded to the cell cluster, the relative amount of cytosolic Ca(2+) was recorded, and ICC were identified by c-Kit immunoreactivity. We specifically detected Ca(2+) oscillation in ICC in the presence of dihydropyridine, which abolishes Ca(2+) oscillation in smooth muscles. The oscillation was coupled to the electrical activity corresponding to slow waves, and it depended on Ca(2+) 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 Ca(2+) oscillation in ICC is intimately linked to the pacemaker function and depends on Ca(2+) influx mediated by TRP4.