Effects of Na and Ca on the generation and conduction of excitation in the ureter

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Abstract
Effects of Na+ and Ca++ on the generation and the conduction of excitation were studied by using a pelvis ureter specimen of cat. Action potentials were recorded simultaneously from the renal pelvis and the various regions of the ureter, and they were used to indicate the arrival of excitation. In Na+-deficient solutions, both the frequency of excitation and the conduction velocity decreased gradually, and finally a conduction block occurred at the border between the renal pelvis and ureter. In Na+-free solution spontaneous excitation was not observed in most cases. When excess Ca++ was added to Na+-free solution, spontaneous excitation was restored, but the concentration of Ca++ necessary for the restoration had to be at least twice that in normal Ringer-Krebs solution. The difference between the ureter and taenia coli was considered with regard to the role that Na+ and Ca++ play in the generation of spontaneous excitation.