Organ specificity of the dopamine1 receptor/adenylyl cyclase coupling defect in spontaneously hypertensive rats

Abstract

The coupling between the dopamine1 (DA1) receptor and the G protein/adenylyl cyclase (AC) enzyme complex is defective in the proximal convoluted tubule (PCT) of 20-wk-old spontaneously hypertensive rats (SHRs). Because this coupling defect could have been due to desensitization secondary to elevated renal dopamine levels in the adult animal, we studied the interaction between DA1 receptors and AC in PCT of rats as early as 3 wk of age, a time when renal dopamine levels are similar in SHRs and their normotensive controls (Wistar-Kyoto rats, WKYs). Maximum receptor density did not change with age and was similar in WKYs and SHRs in all the age groups studied (3, 8, and 20 wk). Basal-, forskolin-, and guanyl nucleotide-stimulated AC activities were also similar in WKYs and SHRs and did not change with age. However, the DA1 agonist-stimulated AC activity was greater in WKYs than in SHRs and increased with age in WKYs but not in SHRs. Moreover, the ability of a nonhydrolyzable analogue of GTP, Gpp(NH)p, to enhance DA1 agonist (SND-919-C12, 1 microM)-stimulated AC activity increased with age in WKY but not in SHRs. To determine if the defect noted in the PCT of SHRs is due to a defective D1A receptor gene, parallel studies were performed in the striatum, since this receptor is expressed predominantly in the latter tissue. In contrast to the results in PCT, radioligand binding and AC studies in striatum revealed no differences between WKYs and SHRs.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat Strain Effects of AT 1 Receptor Activation on D 1 Dopamine Receptors in Immortalized Renal Proximal Tubule Cells

“…However, in SHR cells, this upregulation of D 1 receptors by stimulation of AT 1 receptors is lost because of decreased responsiveness of the hyperphosphorylated D 1 receptor. 46,52,53 We have reported that the renal D 1 receptor is hyperphosphorylated in SHRs as a consequence of increased activity of GRK4 54 and decreased protein phosphatase 2A activity. 49 Long-term incubation with angiotensin II decreases D 1 /AT 1 receptor coimmunoprecipitation to the same degree in cells from SHR and WKY rats.…”

“…We found that cell surface membrane expression of D 1 receptors is lower and D 1 receptor phosphorylation is higher in SHR cells than in WKY cells, although total and D 1 receptor expression are not different in the 2 cell lines. 46,54 Renal D 1 receptor phosphorylation and GRK4 activity impact on the regulation of blood pressure. Inhibition of renal GRK4 activity by antisense oligonucleotides attenuates the increase in blood pressure with age in SHRs without affecting blood pressure in WKY rats.…”

Role of the D1A dopamine receptor in the pathogenesis of genetic hypertension.

“…This phenomenon is not due to differences in D l receptor density, D l antagonist affinity, G-proteins, effector enzyme activity per se, renal brush border Na ϩ /H ϩ exchanger or Na in the renal proximal tubules of SHR occurs as early as 3 wk of age and is receptor, organ, and nephron segment specific (18,23,24). Thus, dopamine and D l agonists stimulate adenylyl cyclase activity in the striatum and the cortical collecting duct to a similar extent in the SHR and in its normotensive control, the Wistar-Kyoto rat (WKY) (18,23,24); parathyroid hormone stimulates adenylyl cyclase activity in renal proximal tubules to a similar extent in SHR and WKY (18). Impaired transduction of the renal D 1 receptor has also been reported in another model of genetic hypertension, the Dahl salt sensitive rat (14,22).…”

“…Prior to radioligand binding the pellet was thawed on ice and washed in Dulbecco's PBS (pH 7.4) containing glucose (1 grams/liter). Radioligand binding was performed using 125 I-SCH 23982, a D 1 antagonist; non-specific binding was defined by 1 M SCH 23390 as described previously (18,20,(22)(23)(24)(25).…”

“…In the SHR, the diminished ability of dopamine and D l agonists to inhibit Na ϩ /H ϩ exchange and Na ϩ /K ϩ ATPase activity in the kidney is due, at least in part, to their impaired ability to stimulate production of second messenger effector enzymes (adenylyl cyclase, phospholipase C) (14,(18)(19)(20)(21)(22). This phenomenon is not due to differences in D l receptor density, D l antagonist affinity, G-proteins, effector enzyme activity per se, renal brush border Na ϩ /H ϩ exchanger or Na in the renal proximal tubules of SHR occurs as early as 3 wk of age and is receptor, organ, and nephron segment specific (18,23,24). Thus, dopamine and D l agonists stimulate adenylyl cyclase activity in the striatum and the cortical collecting duct to a similar extent in the SHR and in its normotensive control, the Wistar-Kyoto rat (WKY) (18,23,24); parathyroid hormone stimulates adenylyl cyclase activity in renal proximal tubules to a similar extent in SHR and WKY (18).…”