Co-contribution of IP₃R and Ca²⁺ Influx Pathways to Pacemaker Ca²⁺ Activity in Stomach ICC:

Intracellular Ca2+ oscillations in interstitial cells of Cajal (ICCs) are thought to be the primary pacemaker activity in the gut. In the present study, the authors prepared small tissues of 100-to 300-µm diameter (cell cluster preparation) from the stomach smooth muscle (including the myenteric plexus) of mice by enzymatic and mechanical treatments. After 2 to 4 days of culture, the intracellular Ca2+ concentration ([Ca2+]i) was measured. In the presence of nifedipine, a dihydropyridine Ca2+ channel antagonist, spontaneous [Ca2+]i oscillations were observed within limited regions showing positive c-Kitimmunoreactivity, a maker for ICCs. In the majority of cell cluster preparations with multiple regions of [Ca2+]i oscillations, [Ca2+]i oscillated synchronously in the same phase. Asmall number of cell clusters (8 of 53) showed multiple regions of [Ca2+]i oscillations synchronized but with a considerable phase shift. Neither tetrodotoxin (250 nM) nor atropine (10µM) significantly affected [Ca2+]i oscillatio...