[Investigation into gastrointestinal pacemaker mechanism using cultured cell cluster preparation]

Gastrointestinal tract motility is driven by pacemaker depolarization referred to slow waves. In order to investigate mechanisms underlying the spontaneous rhythmicity, we have developed a cell cluster preparation. Cell clusters were enzymatically isolated from the muscle layers of mouse small intestine and cultured for several days. They include smooth muscle, enteric neurons and c-Kit-immunopositive cells (interstitial cells of Cajal: ICC), and preserve spontaneous mechanical and electrical activities. A characteristic feature of the pacemaker potential is resistance to dihydropyridine (DHP) Ca(2+) antagonist. In the presence of nifedipine, a DHP Ca(2+) antagonist, spontaneous intracellular Ca(2+) ([Ca(2+)](i)) oscillation was recorded from c-Kit-immunopositive cells in the cell cluster preparation. The [Ca(2+)](i) oscillation seen in ICC was terminated by applications of drugs affecting ryanodine receptors as well as those for InsP(3) receptors and TRP family channels. It is considered that these intracellular Ca(2+) release channels and the Ca(2+) influx pathway from the extracellular space cooperate to produce pacemaker activity in the gastrointestinal tract.