Visualization of origins and propagation of excitation in canine gastric smooth muscle

Visualization of origins and propagation of excitation in canine gastric sm ooth muscle. Am. J. Physiol. 277 (Cell Physiol. 46): C448-C460, 1999.-The o rigin and spread of excitation were visualized with fluo 3 fluorescence in tissues isolated from canine gastric antrum. Sheets of circular muscle (5 x 6 mm) had at least 1 (30%) and up to 3 discrete slow-wave pacing sites loc ated near the longitudinal-circular muscle boundary, whereas similarly size d longitudinal sheets had an average of 5 sites (range 3-12 sites) that ini tiated Ca2+ waves. Superimposed fluorescent oscillations (circular muscle) and spikes (longitudinal muscle) were seen to initiate and propagate as dis tinct events, separate from their underlying activities. Average propagatio n velocities transverse (6-7 mm/s) and parallel (39-45 mm/s) to the long ax is of muscle fibers were similar for each type of event in circular and lon gitudinal tissues; however, distinct regions where velocities of some (but not all) events decreased by up to an order of magnitude were present. The distance propagated by individual events was limited by collisions with con current excitable events or recently activated regions. Complex patterns of excitation in gastrointestinal smooth muscle arise as a result of interact ions between multiple pacing sites, heterogeneous conduction velocities, an d the interplay of adjacent pacemaker domains.