AJP - Renal Physiology, Vol 260, Issue 2 204-F209, Copyright © 1991 by American Physiological Society
Rat kidney band 3 mRNA modulation in chronic respiratory acidosis
J. C. Da Silva Junior, R. D. Perrone, C. A. Johns and N. E. Madias
Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts.
Recent evidence indicates the existence of a protein related to the
erythroid chloride-bicarbonate exchanger (band 3 protein) in the
basolateral aspect of type A intercalated cells of the distal nephron. To
probe the possible participation of this transporter in the renal
adaptation to chronic hypercapnia, we examined the steady-state abundance
of band 3 mRNA in the kidney during respiratory acidosis of variable
duration. Total RNA was isolated from renal cortex and medulla of rats
maintained in a 10% CO2 atmosphere for 2 or 5 days and from contemporaneous
controls. The RNA was analyzed by Northern blot assay using cDNA probes for
band 3 and beta-actin genes. Using a 3' cDNA probe encoding the
membrane-associated domain of band 3 protein that is involved in anion
exchange, we found a two- to threefold increase in steady-state mRNA levels
(whether or not correction for the beta-actin signals was applied) in renal
cortex and medulla at 5 days of hypercapnia. Similar, but less definitive,
increases were observed at the 2-day time point. Using a 5' cDNA probe
encoding an erythroid-protein segment absent from the kidney band 3 major
transcript, we detected meager hybridization in renal tissue and no
measurable variation during hypercapnia. Use of splenic RNA as a positive
control for the 5' probe disclosed marked reduction of band 3 mRNA levels
in hypercapnia, indicating organ specificity of band 3 gene expression. We
conclude that steady-state levels of kidney band 3 mRNA increase in chronic
respiratory acidosis as a result of transcriptional or posttranscriptional
regulatory mechanisms. This adaptation might be involved in the
augmentation of renal acidification characteristic of chronic hypercapnia.
