AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1470-R1477, Copyright © 1991 by American Physiological Society
Indirect coupling of organic anion secretion to sodium in teleost (Paralichthys lethostigma) renal tubules
D. S. Miller and J. B. Pritchard
Section of Intracellular Regulation, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709.
Recent findings in both rat and crab indicate that renal accumulation of
p-aminohippurate (PAH) across the basolateral membrane can be coupled
indirectly to the Na gradient through PAH-glutarate exchange and
Na/glutarate cotransport. However, the role of this mechanism in net
transepithelial PAH secretion was not examined. Therefore, proximal tubules
from Southern flounder kidney were used to assess both the presence of
indirect coupling in the fish and its relationship to net secretion.
[14C]glutarate uptake by proximal tubular masses was concentrative, Na
dependent, and Li inhibitable. Glutarate efflux from preloaded masses was
stimulated by addition of PAH to the medium. Thus flounder tubules
exhibited both Na/glutarate uptake and glutarate-PAH exchange. Furthermore,
steady-state [3H]PAH accumulation was increased 50% by 10-50 microM
glutarate, and this increase was abolished by Li, indicating indirect
coupling of PAH entry to Na. To determine whether indirect coupling
affected net secretion as well as tissue accumulation, the steady-state
accumulation of an anionic dye, fluorescein (FL), was measured in
individual renal tubules by use of epifluorescence microscopy and
video-image analysis. FL accumulated in tubules to levels that were 20-40
times higher than the medium. In most fish, luminal fluorescence was
measurably higher than cellular, and uptake in both compartments was
markedly reduced by PAH and Li. Moreover, FL accumulation in cells and
lumina was increased by 70-100% when 50 microM glutarate was added to the
bathing medium. Thus glutarate not only stimulated uphill FL entry into the
cells, but also stimulated active secretion into the tubular
lumen.(ABSTRACT TRUNCATED AT 250 WORDS)
