Dopamine ₁ Receptor, G _sα , and Na ⁺ -H ⁺ Exchanger Interactions in the Kidney in Hypertension

Abstract

Abstract-The ability of dopamine 1 (D 1 ) receptors to inhibit luminal Na ϩ -H ϩ exchanger (NHE) activity in renal proximal tubules and induce a natriuresis is impaired in spontaneously hypertensive rats (SHR). However, it is not clear whether the defect is at the level of the D 1 receptor, G s␣ , or effector proteins. The coupling of the D 1 receptor to G s␣ and NHE3 was studied in renal brush border membranes (BBM), devoid of cytoplasmic second messengers. D 1 receptor, G s␣ , and NHE3 expressions were similar in SHR and their normotensive controls, Wistar-Kyoto rats (WKY). Guanosine-5Ј-O-(3-thiotriphosphate) (GTP␥S) decreased NHE activity and increased NHE3 linked with G s␣ similarly in WKY and SHR, indicating normal G s␣ and NHE3 regulation in SHR. However, D 1 agonists increased NHE3 linked with G s␣ in WKY but not in SHR, and the inhibitory effects of D 1 agonists on NHE activity were less in SHR than in WKY. Moreover, GTP␥S enhanced the inhibitory effect of D 1 agonist on NHE activity in WKY but not in SHR, suggesting an uncoupling of the D 1 receptor from G s␣ /NHE3 in SHR. Similar results were obtained with the use of immortalized renal proximal tubule cells from WKY and SHR. We conclude that the defective D 1 receptor function in renal proximal tubules in SHR is proximal to G s␣ /effectors and presumably at the receptor level. The mechanism(s) responsible for the uncoupling of the D 1 receptor from G proteins remains to be determined. Because the primary structure of the D 1 receptor is not different between normotensive and hypertensive rats, differences in D 1 receptor posttranslational modification are possible. Key Words: dopamine Ⅲ receptors, dopamine Ⅲ G protein Ⅲ rats, inbred SHR R enal dopamine production, dopamine receptors, and dopamine receptor regulation are important in the pathogenesis of hypertension. 1 Dopamine, produced by renal proximal tubules, is an important paracrine/autocrine inhibitor of renal sodium transport under conditions of sodium loading. 1 The inhibition of sodium transport in renal proximal tubules by dopamine is exerted via the Na ϩ -H ϩ exchanger (NHE) at the luminal or brush border membrane (BBM) and via Na ϩ ,K ϩ -ATPase at the basolateral membrane. 1 The major transport of sodium across the luminal membrane of renal proximal tubules is caused by NHE activity. 2 Five of the 6 isoforms of NHE are expressed in the kidney. 3,4 However, the NHE3 isoform predominates in the BBM of rat renal proximal tubules. 2,5 There is an impaired ability of dopamine 1 (D 1) -like receptors to inhibit NHE activity in BBM of the spontaneously hypertensive rat (SHR). 1 The decreased inhibitory effect of D 1 -like receptors on NHE activity in renal proximal tubules and failure to induce a natriuresis cosegregate with hypertension in SHR and normotensive WistarKyoto rat (WKY) crossbreeds. 6 However, it is not clear whether the impaired inhibitory action of D 1 -like receptors on NHE activity is at the receptors, G proteins, signal transducers, or effectors. G proteins can regulate NHE acti...

Dopamine, hypertension and obesity

“…16 In spontaneously hypertensive rats (SHR)-a model of genetic hypertension-a decrease in DA capability to inhibit this type of hypertension has been demonstrated; this has been attributed to a lower expression and activity of G s protein and a higher expression and activity of G protein. 34 This is the result of a failure in the post-transductional mechanism of the recep-tors, since there is no decrease in the number of D 1 receptors or demonstrable alterations in its structure. 34 Na + /K + /ATPase pump The Na + /K + /ATPase pump, after using ATP, introduces two K + molecules and expels three Na + molecules; this electric gradient is further used for water and Na + resorption.…”

“…34 This is the result of a failure in the post-transductional mechanism of the recep-tors, since there is no decrease in the number of D 1 receptors or demonstrable alterations in its structure. 34 Na + /K + /ATPase pump The Na + /K + /ATPase pump, after using ATP, introduces two K + molecules and expels three Na + molecules; this electric gradient is further used for water and Na + resorption. DA reversibly inhibits this pump, mainly through type 1 receptors, which results in an increase in natriuresis.…”

Inhibition of D 4 Dopamine Receptors on Insulin Receptor Expression and Effect in Renal Proximal Tubule Cells

“…In order to test the above hypotheses, we studied D 4 and insulin receptor interaction in immortalized RPT cells from Wistar‐Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). These RPT cells behave similarly to freshly obtained RPT cells, at least with regard to dopamine receptors and responses to G‐protein stimulation 14, 15…”

D3 dopamine receptor regulation of D5 receptor expression and function in renal proximal tubule cells

“…[16][17][18][19][20] Those RPT cells were from Ulrich Hopfer's laboratory in Case Western Reserve School of Medicine (Cleveland, OH, USA). HEK293 cells were transfected with the human D 5 receptor complementary DNA (cDNA) fused to a V5-His tag at the C-terminus or the empty vector (pcDNA6/V5-His) (36), which served as a control.…”

“…These RPT cells behave similarly to freshly obtained RPT cells, at least with regard to dopamine receptors and responses to G protein stimulation. [17][18][19][20] …”