Involvement of ryanodine receptors in pacemaker Ca2+ oscillation in murine gastric ICC

Using a cell cluster preparation from the stomach smooth muscle tissue of mice, we measured intracellular Ca2+ oscillations in interstitial cells of Cajal (ICCs) in the presence of nifedipine. Pacemaker [Ca2+]i activity in ICCs was significantly suppressed by caffeine application and restored after washout. Application of either ryanodine or FK-506 terminated the pacemaker [Ca2+]i activity irreversibly. Immunostaining of smooth muscle tissue showed that c-Kit-immunopositive cells (that form network-like structure cells in the myenteric plexus, equivalent to ICCs) clearly express ryanodine receptors (RyR). RT-PCR revealed that ICCs (identified with c-Kit-immunoreactivity) predominantly express type 3 RyR (RyR3). Furthermore, the FK-binding proteins 12 and 12.6, both of which would interact with RyR3, were detected. In conclusion, we provide first evidence for the essential contribution of RyR to generating pacemaker activity in gastric motility. Similar mechanisms might account for spontaneous rhythmicity seen in smooth muscle tissues distributed in the autonomic nervous system.