Dexamethasone Increases Adrenalectomy‐Depressed Na⁺,K⁺‐ATPase mRNA and Ouabain Binding in Spinal Cord Ventral Horn

Abstract

The Na+,K'-ATPase plays a key role in the regulation of ion fluxes and membrane repolarization in the CNS . We have studied glucocorticoid effects on biosynthesis of the Na+,K+-ATPase and on ouabain binding in the ventral horn of the spinal cord using intact rats, adrenalectomized (ADX) rats, and ADX rats receiving dexamethasone (ADX + DEX) during 4 days . Cryostat sections from spinal cords were incubated with a 35Soligonucleotide coding for the a3-subunit or a 3H-cDNA coding for the 01-subunit of the Na+,K+-ATPase using in situ hybridization techniques . In ventral horn motoneurons, grain density per cell and grain density per area of soma for both probes were slightly reduced in ADX rats but significantly increased in the ADX + DEX group, using ANOVA and the Bonferroni's test . Statistical analysis of frequency histograms of neuronal densities further indicated a significant shift to the right for intact rats compared with ADX rats for both probes . Concomitantly, [3 H]ouabain binding to membrane preparations from ventral horns was reduced in ADX rats and restored to normal by DEX administration . No effect of adrenalectomy or DEX treatment was obtained in the dorsal horn . In conclusion, glucocorticoids positively modulate the mRNA for the a3-subunit and the Q1 -subunit of the Na+,K+-ATPase and recover ouabain binding to normal values . The increments of the synthesis and activity of an enzyme affecting membrane repolarization and synaptic neurotransmission are consistent with the alleged stimulatory effect of glucocorticoids on spinal cord function .

Transcriptional regulators of Na,K-ATPase subunits

“…Hormones are major regulators of Na,K-ATPase expression. Mineralocorticoids (Verrey et al, 1987 , 1988 , 1989 ; Ikeda et al, 1991 ; Oguchi et al, 1993 ; Farman et al, 1994 ; Muto et al, 1996 ; Tsuchiya et al, 1996 ; Grillo et al, 1997 ; Seok et al, 1999 ; Olivera et al, 2000 ; Blot-Chabaud et al, 2001 ; Phakdeekitcharoen et al, 2011 ), glucocorticoids (Orlowski and Lingrel, 1990 ; Bhutada et al, 1991 ; Celsi et al, 1991 ; González et al, 1994 , 1996 ; Muto et al, 1996 ; Barquin et al, 1997 ; Ingbar et al, 1997 ; Chalaka et al, 1999 ; Dagenais et al, 2001 ; Hao et al, 2003a , b ), thyroid hormone (McDonough et al, 1988 ; Gick and Ismail-Beigi, 1990 ; Orlowski and Lingrel, 1990 ; Melikian and Ismail-Beigi, 1991 ; Hensley et al, 1992 ; Kamitani et al, 1992 ; Azuma et al, 1993 ; Giannella et al, 1993 ; Ohara et al, 1993 ; Huang et al, 1994 ; Lin and Tang, 1997 ; Bajpai and Chaudhury, 1999 ; Shao et al, 2000 ; Phakdeekitcharoen et al, 2007 ), insulin (Russo and Sweadner, 1993 ; Tirupattur et al, 1993 ; Sweeney and Klip, 1998 ), progesterone (Cochrane et al, 2012 ; Deng et al, 2013 ), androgen (Blok et al, 1999 ), and vitamin D3 (Billecocq et al, 1997 ) have been reported to activate or repress Na,K-ATPase transcription. These hormones bind to and activate their receptors, which belong to the family of nuclear receptors with C4 zinc-fingers that then translocate into the nucleus to bind to the promoter regions of the target genes to regulate gene expression.…”

“…Glucocorticoids regulate the transcription of Na,K-ATPase in a variety of tissues including lung, kidney, liver, heart, spinal cord, cardiac muscle and smooth muscle (Orlowski and Lingrel, 1990 ; Bhutada et al, 1991 ; Celsi et al, 1991 ; Wang and Celsi, 1993 ; González et al, 1994 , 1996 ; Wang et al, 1994 ; Muto et al, 1996 ; Barquin et al, 1997 ; Ingbar et al, 1997 ; Chalaka et al, 1999 ; Dagenais et al, 2001 ; Hao et al, 2003b ). This regulation is specific to the cell type and the developmental stage.…”