title: Dopamine-mediated inhibition of renal Na,K-ATPase is reduced by insulin.
abstract: Recently we have reported that rosiglitazone treatment of obese Zucker rats reduced plasma insulin and restored the ability of dopamine to inhibit Na,K-ATPase (NKA) in renal proximal tubules. The present study was performed to test the hypothesis that a chronic increase in levels of insulin causes a decrease in expression of the D1 receptor and its uncoupling from G proteins, which may account for the diminished inhibitory effect of dopamine on NKA in obese Zucker rats. We conducted experiments in primary proximal tubule epithelial cells obtained from Sprague-Dawley rat kidneys. These cells at 80% to 90% confluence were pretreated with insulin (100 nmol/L for 24 hours) in growth factor-/serum-free medium. SKF-38393, a D1 receptor agonist, inhibited NKA activity in untreated cells, but the agonist failed to inhibit enzyme activity in insulin-pretreated cells. Basal NKA activity was similar in untreated and insulin-pretreated cells. Measurement of D1 receptors in the plasma membranes revealed that [3H]SCH-23390 binding, a D1 receptor ligand, as well as D1 receptor protein abundance, was significantly reduced in insulin-pretreated cells compared with untreated cells. SKF-38393 (10 micromol/L) elicited significant stimulation of [35S]GTPgammaS binding in the membranes from control cells, suggesting that the D1 receptor-G protein coupling was intact. However, the stimulatory effect of SKF-38393 was absent in membranes from insulin-pretreated cells. We suggest that chronic exposure of cells to insulin causes both the reduction in D1 receptor abundance and its uncoupling from G proteins. These phenomena might account for the diminished inhibitory effect of dopamine on NKA activity in hyperinsulinemic rats.
authors.affiliation: Heart and Kidney Institute, University of Houston, Houston, Tex 77204, USA.
authors.forename: Anees Ahmad
authors.initials: AA
authors.lastname: Banday
authors.forename: Mohammad
authors.initials: M
authors.lastname: Asghar
authors.forename: Tahir
authors.initials: T
authors.lastname: Hussain
authors.forename: Mustafa F
authors.initials: MF
authors.lastname: Lokhandwala
mesh_terms: D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000037:antagonists & inhibitors*; D000818:Animals; D001552:Benzazepines / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D018491:Dopamine Agonists / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
chemical_list: D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D007328:Insulin; D017447:Receptors, Dopamine D1; C098593:dopamine D1A receptor; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D000254:Sodium-Potassium-Exchanging ATPase