Effects of postnatal steroids on Na+/K+-ATPase activity and α1- and β1-subunit protein expression in the cerebral cortex and renal cortex of newborn lambs
Chang-Ryul Kim A B , Grazyna B. Sadowska A , Katherine H. Petersson A , Maricruz Merino A , Gregory D. Sysyn A , James F. Padbury A and Barbara S. Stonestreet A C
+ Author Affiliations
- Author Affiliations
A Pediatrics, Women & Infants’ Hospital of Rhode Island and Brown Medical School, Providence, RI 02905-2499, USA.
B Current address: Pediatrics, Hanyang University College of Medicine, Seoul, Korea.
C Corresponding author. Email: bstonestreet@wihri.org
Reproduction, Fertility and Development 18(4) 413-423 https://doi.org/10.1071/RD05114
Submitted: 22 September 2005 Accepted: 2 January 2006 Published: 22 March 2006
Abstract
Na+/K+-ATPase is a membrane-bound enzyme responsible for Na+/K+ translocation across cell membranes. It is essential for the generation of electrochemical gradients, which control the ionic environment necessary for electrical activity and water and electrolyte balance. Newborn infants who are at risk of developing bronchopulmonary dysplasia (BPD) are frequently treated with corticosteroids. Although these infants are at risk for neurological, water and electrolyte abnormalities, there is little information regarding the effects of clinically relevant doses of corticosteroids on Na+/K+-ATPase activity and protein isoform expression in the brain and kidney of newborns. In the present study, we examined the effects of dexamethasone on cerebral cortical and renal cortical Na+/K+-ATPase activity and α1- and β1-protein isoform expression in newborn lambs. Lambs were given four injections of a placebo (n = 11) or one of three different doses of dexamethasone (0.01 mg kg−1, n = 9; 0.25 mg kg−1, n = 11; or 0.50 mg kg−1, n = 9) 12 h apart on Postnatal Days 3 and 4 up to 18 h before harvest of the cerebral cortex and renal cortex. We selected doses in a range to approximate those used to treat infants with BPD. Na+/K+-ATPase activity was measured in membrane preparations as ouabain-sensitive inorganic phosphate liberation from ATP and α1- and β1-subunit abundance by Western immunoblot. Postnatal treatment of lambs with dexamethasone resulted in a 21.4% increase in Na+/K+-ATPase activity and a 30.4% increase in catalytic α1-protein expression in the cerebral cortex at a dose of 0.50 mg kg−1 dexamethasone, but not at the lower doses. Dexamethasone treatment was not associated with changes in β1-isoform expression in the cerebral cortex. In the kidney, dexamethasone treatment was not associated with significant changes in Na+/K+-ATPase activity or α1- or β1-isoform expression for the doses we examined. Therefore, clinically relevant corticosteroid treatment exerts dose-related, differential organ-specific effects on Na+/K+-ATPase activity and protein isoform expression in newborn lambs.
Extra keywords: brain, corticosteroids, kidney, sheep.
Acknowledgments
The authors are grateful to Dr Alicia M. McDonough (Physiology and Biophysics, University of Southern California, Los Angeles, CA, USA) for her assistance and guidance in setting up the Na+/K+-ATPase activity and Western blot subunit assays in their laboratory, as well as for her general expert guidance during the development of this project. This work was supported by the National Institute of Child Health and Human Development Grant R01-HD-34618.
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