Gradient of total [Ca++] in the renal pelvis.

The [Ca++] gradient within the rabbit renal pelvis was compared to its inherent pacemaker frequency. The pelvis was removed from the rabbit, sectioned, and [Ca++] ions assayed using wet ash techniques and atomic absorption spectrophotometry. Contraction frequency was measured isometrically in vitro. In the bisected pelvis it was found that both [Cu++] levels and contraction frequency were highest in the proximal section, 9.02 +/- 4.62 mEq/kg, and lower in the distal section, 6.59 +/- 2.43 mEq/kg wet weight. The mean frequency of contraction decreased from 3.69 +/- 0.81 to 2.41 +/- 0.49 min-1 in the proximal and distal regions, respectively.