Multiple-coupled pacemaker system in renal pelvis of the unicalyceal kidney

The characteristics of spontaneous contractility in the renal pelvis were examined in the unicalyceal kidney of the rabbit. In vitro isometric studies were done on whole as well as renal pelvic segments dissected longitudinally and radially. The results show that the contractile frequency of isolated segments was highest in the proximal region (4.188 +/- 0.162 min-1) and decreased distally to (2.178 +/- 0.330 min-1). There was no significant frequency gradient in the circumferential direction. A modulation of wave form (waxing and waning phenomena) was observed in both the proximal and middle regions of the pelvis. Based on these results, a simulation of the renal pelvic activity was made by using a chain of coupled linear oscillators. At high values of coupling a pacemaker contraction of the renal pelvis was reproduced by the coupled oscillator model. The modulation of wave form was observed when the coupling of the circumferential direction was weak. These results are discussed in the context of the hierarchically organized multiple-coupled pacemaker system, which characterizes an integrative activity of the unicalyceal renal pelvis.