Mechanism of the pacemaker activity in the upper urinary tract, especially how single pacemaker cells form a pace maker region, has not been fully documented. To approach this problem, we developed in situ Ca2+ imaging technique of the rat utero-pelvic preparation using a macro zoom microscope (Olympus MVX 10). The bright clear view and smooth zooming operation with this technique enabled us to search upstream of Ca2+ transient and to identify the pacemaker region easily. Using the same technique we could also successfully record image of di-4-ANEPPS, a voltage-sensitive dye. The initial depolarization occurred at the exactly same place as the Ca2+ transient began. With higher magnification , we could observe that not only one cell but several cells increased their intracellular Ca2+ concentration simultaneously. Their propagating pathway were slightly different every time. Interestingly spontaneous Ca2+ rises in single cells were observed in the other part of renal pelvis and even in the ureter. They are not synchronous to the pristaltic movement and rarely propagated to neighboring cells. In the presence of low concentration of heptanol, a gap junction blocker, the cells forming the pacemaker region lost their synchronism and their function as the pacemaker. These results might suggest that summation of electric activity via gap junctions played an important role in the formation of the pacemaker region. [J Physiol Sci. 2007;57 Suppl:S16]
