Initiation and propagation of stimulus from the renal pelvic pacemaker in pig kidney.

A new in vitro method was used to examine the initiation and the propagation of the peristaltic contraction in the renal pelvis and ureter of the pig. The method enabled the direct observation of peristalsis, both microscopically and electrophysiologically. A microscopic ripplelike contraction of a constant frequency was generated spontaneously at the border between the upper, middle, and lower major calyces and their minor calyces. At the same time, electromyograms were recorded in the same regions, with a constant discharge interval that suggested to us that these might be pacemaker potentials. The waves originating from the upper calyx, middle calyx, and lower calyx propagated at different times toward the ureter. Pressure changes of an almost constant interval were recorded in each calyx and corresponded in a 1:1 ratio to the action potentials at the same calyx. Pelvic pressure changes reflected the electrical activity of the renal pelvis, but did not reflect the pacemaker activity of the renal calyx.U