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

• Published in: Journal of biological rhythms 2005-02, Vol.20 (1), p.15-26
• Main Authors: Liu, Hong-Nian, Ohya, Susumu, Furuzono, Shinji, Wang, Jing, Imaizumi, Yuji, Nakayama, Shinsuke
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Biological Transport; Calcium; Calcium - metabolism; Calcium - physiology; Calcium Channels - metabolism; Calcium Channels - physiology; Cellular biology; DNA Primers; In Vitro Techniques; Inositol 1,4,5-Trisphosphate Receptors; Membrane Glycoproteins - metabolism; Membrane Glycoproteins - physiology; Mice; Mice, Inbred BALB C; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Muscle, Smooth - physiology; Receptors, Cytoplasmic and Nuclear - metabolism; Receptors, Cytoplasmic and Nuclear - physiology; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; Stomach; Stomach - drug effects; Stomach - metabolism; Stomach - physiology; Tetrodotoxin - pharmacology
• ISSN: 0748-7304; 1552-4531
• DOI: 10.1177/0748730404269572

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 oscillations in the presence of nifedipine. Low concentrations (40µM) of Ni2+ had little effect on the spontaneous [Ca2+]i oscillation, but SK&F96365 (40µM) and Cd2+ (120µM) terminated it. Applications of either 2-aminoethoxydiphenyl borate (10µM) or xestosponginC(10µM) completely and rather rapidly (~2 min) abolished the spontaneous [Ca2+]i oscillations. The results suggest that pacemaker [Ca2+]i oscillations in ICCs are produced by close interaction of intracellular Ca2+ release channels, especially inositol 1,4,5-trisphosphate receptor (InsP3R) and Ca2+ influx pathways, presumably corresponding to store-operated type channels. Reverse transcription polymerase chain reaction examinations revealed expression of TRPC2, 4, and 6, as well as InsP3R1 and 2 in ICCs.