Inhibition of IMCD 11 beta-hydroxysteroid dehydrogenase type 2 by low pH and acute acid loading.
Mineralocorticoid receptors in the inner medullary collecting duct (IMCD) are protected from glucocorticoid binding by an enzyme, 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2). To study the role of 11 beta-HSD2 in acid-base homeostasis, 11 beta-HSD2 activity was measured in rat IMCD-enriched cell suspensions. Homogenates of cell suspensions were incubated in buffers ranging in pH from 6.00 to 8.15 in the presence of 1 microCi of 3H-corticosterone (CS) and 400 microM NAD+. Enzyme activity was expressed as the amount of 3H-CS converted to 3H-11-dehydrocorticosterone (DHCS). IMCD 11 beta-HSD2 activity at pH 6.5 was 49% of activity at pH 7.5; 22.5 versus 11.0 fmol/microgram of protein per h. Experiments also were performed on intact cell suspensions at pH 7.5 and 6.5. There was a 42% inhibition in the IMCD cell suspension conversion rate of 3H-CS to 3H-11-DHCS at pH 6.5; 13.1 versus 7.6 fmol/microgram per h (P < 0.005). In cell suspensions at pH 7.5, 1-day acid loading caused a 26% inhibition in conversion rate, 13.2 versus 9.9 fmol/microgram per h (P < 0.05), when compared with controls. These results suggest that during acute metabolic acidosis, IMCD 11 beta-HSD2 is inhibited and may allow access to the mineralocorticoid receptors by glucocorticoids.
Nolan
P J
PJ
Department of Biological Sciences, George Washington University, Washington, DC 20052, USA.
Knepper
M A
MA
Packer
R K
RK
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D003345:Corticosterone / Q000378:metabolism*; D005938:Glucocorticoids / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D066298:In Vitro Techniques; D007685:Kidney Tubules, Collecting / Q000201:enzymology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D018161:Receptors, Mineralocorticoid / Q000378:metabolism
D005938:Glucocorticoids; D018161:Receptors, Mineralocorticoid; D006913:Hydroxysteroid Dehydrogenases; D042842:11-beta-Hydroxysteroid Dehydrogenases; D003345:Corticosterone