Heterogeneity of uridine incorporation along the rabbit nephron. I. Autoradiographic study

We present here an autoradiographic study of uridine labeling in tubular segments micro-dissected from the rabbit kidney. Kidney pyramids were incubated for 60 min with low (66 nM) and high (66 microM) [3H]-uridine concentration. At the two concentrations studied the labeling was almost exclusively nuclear in all segments studied. At the low concentration, labeling predominated in the macula densa (MD = 63.88 +/- 6.15 silver grains/100 micron2, n = 11), cortical ascending limb (CAL = 19.65 +/- 1.65, n = 15), and initial distal tubule (DCTa = 24.31 +/- 2.70, n = 6). It was minimal in the proximal tubule (PCT2 = 9.14 +/- 1.61, n = 16) and in the cortical (CCT = 5.23 +/- 0.75, n = 18) and medullary (MCT = 5.52 +/- 1.10, n = 12) collecting ducts. At a high concentration, the profile of labeling was roughly similar except for a relative increase in labeling much more pronounced in collecting ducts (CCT = +373, MCT = +323%) than in the other structures (MD = -14, CAL = +66, DCTa = +49, PCT = +9%). Pulse-chase experiments do not show evidence for differences in turnover or degradation rates of RNA between segments, at least in the PCT and the connecting part of the CCT. Analysis of the results at low and high concentration suggests that the observed heterogeneity in uridine labeling depends on both variable endogenous nucleoside pools and different rates of uridine incorporation into RNA from one segment to another.