AJP - Renal Physiology, Vol 267, Issue 3 479-F488, Copyright © 1994 by American Physiological Society
Adaptive responses to Na(+)-coupled solute transport and osmotic cell swelling in salamander proximal tubule
S. W. Weinstein and C. Clausen
Department of Medicine, Northport Veterans Affairs Medical Center, New York 11768.
Measurements of basolateral membrane potential and relative K+ conductance
were performed in isolated perfused proximal tubules from Ambystoma. To
investigate adaptive increases in basolateral membrane K+ conductance (gK)
associated with Na(+)-solute cotransport, measurements were made comparing
transport of glucose and alanine, with changes caused by hypotonicity- and
solute-induced cell swelling. Luminal perfusion with alanine produced
results consistent with an adaptive increase in gK; perfusion with glucose
failed to show this response. Hypotonic peritubular solutions also produced
results consistent with an adaptive increase in gK, but isosmotic increases
of peritubular glucose sufficient to swell the cells failed to produce
this. No changes in the responses to luminal perfusion with alanine or
glucose were induced by hypotonic peritubular solutions. With a high
concentration of glucose in isosmotic peritubular solutions, perfusion of
the lumen with glucose now produced results consistent with an adaptive
increase in gK. Isosmotic peritubular solutions containing urea produced
adaptive changes similar to those observed using hypotonic peritubular
solutions, but when glucose was subsequently added to the lumen, no further
adaptive response occurred. We conclude that cell swelling alone is
insufficient to explain the mechanisms involved in the adaptive responses
of gK occurring during Na(+)-solute cotransport in the salamander proximal
tubule.
