AJP - Endocrinology and Metabolism, Vol 264, Issue 1 E45-E53, Copyright © 1993 by American Physiological Society
Stepwise degradation of NT in pars convoluta and recta of rabbit proximal tubules: evidence of axial heterogeneity
T. Bjerke, S. Nielsen, M. I. Sheikh and E. I. Christensen
Department of Cell Biology, University of Aarhus, Denmark.
Reabsorption and degradation of the neuropeptide neurotensin (NT) in rabbit
proximal pars convoluta (PC) and pars recta (PR) nephron segments were
characterized. Brush-border membrane vesicle fractions (PC or PR) were
incubated with [3H]NT, and the extent and pattern of peptide hydrolysis
were determined by reversed-phase high-pressure liquid chromatography
(rHPLC). Furthermore, isolated rabbit PC and PR segments were perfused with
[3H]NT, reabsorption of [3H]NT was quantified, and the collected perfusate
was analyzed by HPLC. Metabolites were characterized. Finally, rabbit
proximal tubules were microinfused in vivo with [3H]NT to follow the
tubular uptake by electron microscope autoradiography. Degradation
increased with time in both vesicle fractions. The main difference was an
extensive cleavage of NT in PR, as revealed by a higher proportion of end
metabolites. This was also visualized as a higher proportion of the large
degradation product in rHPLC fraction 39 [NT-(1-11)] in PC as compared with
PR after 30 min of incubation. The isolated perfused proximal tubular
segments processed NT with large efficiency. PC segments processed 90% of
the perfused amount, and PR processed 88%. Only 13% in PC and 10% in PR of
the processed NT were found in the bath and the tubule. The main part of
processed NT was in the collected perfusate, and rHLPC profiles revealed
that NT-(1-11) was the only metabolite in both PC and PR. Electron
microscope autoradiography demonstrated autoradiographic grains over
invaginations and over the apical part of the proximal tubule cell in
endocytic vesicles and vacuoles 10 min after microinfusion of
[3H]NT.(ABSTRACT TRUNCATED AT 250 WORDS)
