Stimulation Of Vasopressin Receptors Research Articles

Acidosis-induced activation of distal nephron principal cells triggers Gdf15 secretion and adaptive proliferation of intercalated cells.

Type A intercalated cells of the renal collecting duct participate in the maintenance of the acid/base balance through their capacity to adapt proton secretion to homeostatic requirements. We previously showed that increased proton secretion stems in part from the enlargement of the population of proton secreting cells in the outer medullary collecting duct through division of fully differentiated cells, and that this response is triggered by growth/differentiation factor 15. This study aimed at deciphering the mechanism of acid load-induced secretion of Gdf15 and its mechanism of action. We developed an original method to evaluate the proliferation of intercalated cells and applied it to genetically modified or pharmacologically treated mice under basal and acid-loaded conditions. Gdf15 is secreted by principal cells of the collecting duct in response to the stimulation of vasopressin receptors. Vasopressin-induced production of cAMP triggers activation of AMP-stimulated kinases and of Na,K-ATPase, and induction of p53 and Gdf15. Gdf15 action on intercalated cells is mediated by ErbB2 receptors, the activation of which triggers the expression of cyclin d1, of p53 and anti-proliferative genes, and of Egr1. Acidosis-induced proliferation of intercalated cells results from a cross talk with principal cells which secrete Gdf15 in response to their stimulation by vasopressin. Thus, vasopressin is a major determinant of the collecting duct cellular homeostasis as it promotes proliferation of intercalated cells under acidosis conditions and of principal cells under normal acid-base status.

Hyponatremia and V2 vasopressin receptor upregulation: a result of HSP90 inhibition

PurposeSmall-molecule inhibitors of heat-shock protein 90 (HSP90) have been under development as chemotherapeutic agents. The adverse events reported from early clinical trials included hyponatremia. Given the limited number of patients enrolled, the number of hyponatremia incidents was remarkable and repeatedly, the event was judged as severe. Inappropriate V2 vasopressin receptor stimulation is an established cause of hyponatremia. We explored the hypothesis that HSP90 inhibition produces hypersensitivity to vasopressin by upregulating V2-receptors.MethodsExperiments were carried out in cell culture using HEK293 cells with heterologous expression of the human V2-receptor and HELA cells with an endogenous V2-receptor complement. We tested the effect of HSP90 inhibition by three structurally unrelated compounds (alvespimycin, luminespib, radicicol) and asserted its specificity in cells depleted of cytosolic HSP90 (by RNA interference). Assays encompassed surface V2-receptor density and vasopressin-stimulated formation of cyclic AMP (cAMP).ResultsThe results demonstrate a twofold increase in cell-surface receptor density following pre-incubation with each of the HSP90 inhibitors. The effect had a concentration-dependence consistent with the individual potencies to inhibit HSP90. Similarly, depletion of cytosolic HSP90 increased surface-receptor density and at the same time, reduced the inhibitor effect. Upregulated V2-receptors were fully functional; hence, in culture treated with an HSP90 inhibitor, addition of vasopressin resulted in higher levels of cAMP than in controls.ConclusionSince formation of cAMP is the first signalling step in raising water permeability of the collecting duct epithelia, we suggest that V2-receptor upregulation generates hypersensitivity to vasopressin linking HSP90 inhibition to the development of hyponatremia.

PIP2 Dynamics underlying Muscarinic or Vasopressin Receptor-Activated TRPC3 C6 And C7 Currents

Subfamily of human expressed TRPC channels (TRPC3/6/7) are activated by ‘diacylglycerol' (DAG), a phospholipase C (PLC) hydrolyzed product of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] (Hofmann et al., 1999, Nature). In contrary, we have recently reported that the depletion of PI(4,5)P2 by-itself act as a potent negative regulator to all these channels even in the presence of DAG (Imai et al., 2012, J. of Physiol.). Stimulation upon the vasoconstrictile receptors coupled with PLC theoretically causes inseparable bimodal effect to these TRPC channels, i.e. activation and inhibition by DAG production and coincident PI(4,5)P2 reduction or depletion which is corresponding to the strength of PLC activities. Here, to elucidate such self-limiting regulatory function coupled to PI(4,5)P2-DAG signal, we simultaneously measure TRPC6/7 currents in the whole-cell configuration and PI(4,5)P2 dynamics by FRET using PI(4,5)P2 binding PH-domain sensor proteins in the various strength of muscarinic- or vasopressin-receptor stimulation. Our simultaneous detection approach reveals good kinetics correlation between TRPC activation/fast-inactivation and PI(4,5)P2 depletion. Furthermore, a simple self-limiting regulation model wherein experimentally determined PI(4,5)P2 binding constants incorporated aware an emergence of fast recovery of PI(4,5)P2 to produce slow inactivation (plateau phase) of TRPC currents. We find that such model implicated PI(4,5)P2 enhancement can be reproduced after the fast PI(4,5)P2 depletion under the robust agonist stimulation by the local FRET measurement near the channels. Hence, these data indicates that self-limiting regulation coupled to PI(4,5)P2-DAG signal is the pivotal mechanism to understand the receptor-PLC mediated TRPC3/6/7 channels activity.

Vasopressin beyond water: implications for renal diseases

This review aims to analyze the relationships between arginine vasopressin (AVP) and chronic kidney disease (CKD) and to define the potential of vasopressin receptor antagonists beyond the treatment of water metabolism disorders. Experimental studies in rat and observational studies in humans suggest that AVP may play a role in the genesis and exacerbation of renal damage and chronic renal insufficiency. A sustained stimulation of vasopressin receptors induces intrarenal renin-angiotensin system activation, podocyte alterations, glomerular hyperfiltration and hypertrophy eventuating in proteinuria and kidney damage. Furthermore, AVP directly stimulates contraction and proliferation of mesangial cells and accumulation of extracellular matrix and glomerulosclerosis. Whether a chronic increase in water intake (determining a reduction in endogenous AVP levels) and/or the administration of vasopressin receptor antagonists are useful for the prevention and treatment of CKD remains to be tested in clinical trials.

Pressor responsiveness to intravenous quinpirole is blunted in malnourished, conscious rats: central vs. peripheral and spinal mechanisms.

In conscious rats, intravenous treatment with the dopamine D2-like receptor agonist quinpirole, elicited a pressor effect, which is attributed to central dopamine D2 receptor-mediated activation of sympathetic outflow associated with arginine vasopressin release. This prominent central effect is opposed to peripheral sympathoinhibitory and spinal depressor effects. The present study investigated the effects of pre- and postnatal undernutrition on the central pressor responsiveness to quinpirole. Malnourished (MalN) rats were obtained by feeding dams a multideficient diet (providing 8% protein) during pregnancy and nursing. At 90 days of age, MalN rats weighed significantly less than control (CNT) rats born to dams fed standard commercially diet (23% protein) during pregnancy and nursing. Baseline mean arterial pressure and heart rate in MalN rats were comparable to those of CNT. Intravenous treatment with quinpirole (0.3 mg/kg) in MalN conscious rats induced a pressor effect, which was significantly reduced in both magnitude and duration, when compared with CNT rats. In both groups studied, pressor response to quinpirole was fully abolished by the peripheral and central dopamine D2 receptor antagonist, metoclopramide (5 mg/kg, i.v.) whereas was significantly enhanced after pretreatment with either intravenous (0.5 mg/kg) or intrathecal (40 microg per rat at T9-T10 level) domperidone, a dopamine D2 receptor antagonist that does not cross the blood-brain barrier. However, even under peripheral and spinal dopamine D2 receptor blockade, maximum pressor effect of quinpirole remained significantly reduced in MalN when compared with CNT rats. Neither the maximum pressor nor the bradycardiac responses to intravenous phenylephrine or arginine vasopressin differed between CNT and MalN rats. This study shows that undernutrition imposed during fetal life and suckling blunted the pressor response to quinpirole in conscious rats. This blunted response appears mainly related to desensitization of brain dopamine D2 receptors rather than enhanced peripheral and/or spinal dopamine D2 receptor-mediated depressor effect or vascular hyporesponsiveness to alpha1-adrenoceptor and vasopressin receptor stimulation.

Effects of long-term vasopressin receptor stimulation on medullary blood flow and arterial pressure.

Studies were carried out using instrumented unanesthetized rats to determine the long-term effects of arginine vasopressin (AVP) and a specific vasopressin V1 receptor agonist (V1AG; [Phe2, Ile3, Orn8]- vasopressin) on the renal medullary blood flow and arterial blood pressure. It was hypothesized that the hypertension observed with chronic medullary infusion of a V1 receptor agonist may be associated with a sustained reduction of blood flow, whereas infusion of AVP may fail to produce a sustained reduction of blood flow and thereby be unable to produce hypertension. Uninephrectomized Sprague-Dawley rats were prepared with implanted renal cortical and medullary optical fibers for daily measurements of cortical and medullary blood flow using laser-Doppler flowmetry techniques. An implanted renal medullary interstitial infusion catheter delivered either AVP or a specific V1AG at a dose of 2 ng . kg-1 . min-1 over a period of 5 days. The V1AG produced no change of cortical blood flow but a chronic 35% reduction of medullary blood flow (P < 0.05) and mild hypertension (11 +/- 4 mmHg, P < 0.05). AVP produced only an initial, nonsignificant 1- to 2-day reduction of medullary blood flow (-13%) and failed to raise arterial pressure significantly. We conclude that a sustained V1AG response is necessary to achieve a chronic reduction of medullary blood flow and hypertension. The present data are consistent with the idea that chronic stimulation of V2 receptors by AVP offsets the vasoconstrictor and hypertension actions of AVP-induced stimulation of medullary V1 receptors.

Multiple pathways for entry of calcium and other divalent cations in a vasculr smooth muscle cell line (A7r5)

The influx of calcium in response to vasopressin receptor stimulation is an important component of excitation-contraction coupling. We have examined the routes by which Ca 2+ and other divalent cations enter vascular smooth muscle cells using a cultured vascular smooth muscle cell line (A7r5). Confluent A7r5 cells were loaded with Fura-2 to permit measurement of intracellular divalent cation concentration (Ca 2+, Ba 2+, Mn 2+). Combinations of excitation wavelengths ( 340 380 , 340 356 , 356 380 and 340 370 ) were used depending on the divalent cation being studied. Emission was measured at 510 nm for all studies. Ca 2+, Ba 2+ and Mn 2+ permeated unstimulated A7r5 cells. Vasopressin increased intracellular Ca 2+ in cells both in the presence and absence of extracellular Ca 2+, although responses in the absence of extracellular Ca 2+ were smaller and had no sustained component. Amlodipine, a voltage-dependent calcium channel blocker, had no effect on Ca 2+ entry, but Ni 2+ did block Ca 2+ influx. Vasopressin-induced elevations of intracellular Ca 2+ in Ca 2+-free physiological saline were abolished by ionomycin and thapsigargin. In the presence of extracellular Ba 2+ vasopressin increased intracellular Ca 2+ transiently and caused a small sustained increase in intracellular Ba 2+ concentration. Ionomycin and thapsigargin increased intracellular Ca 2+ but had no effect on Ba 2+ influx. In contrast vasopressin, ionomycin and thapsigargin had no effect on Mn 2+ influx. Econazole and SKF 96365, imidazoles reported to be blockers of receptor-induced cation entry, increased intracellular Ca 2+ by releasing intracellular Ca 2+ from a different site to that mobilized by vasopressin or thapsigargin in A7r5 cells. Econazole and SKF 96365 partially inhibited passive influx of Ca 2+ and Ba 2+ but did not inhibit passive influx of Mn 2+, or vasopressin-induced influx of Ba 2+. U73122, a putative inhibitor of phospholipase C partially inhibited passive entry of Ca 2+ but not passive entry of Mn 2+ and Ba 2+. U73122 also inhibited vasopressin-induced release of intracellular Ca 2+ and agonist-induced Ca 2+ influx but did not block vasopressin-induced Ba 2+ influx. Divalent cations enter A7r5 cells by a number of routes — ‘passive’ pathway(s) that admit Ca 2+, Ba 2+ and Mn 2+ and receptor-operated pathway(s) that are permeable to Ca 2+, Ba 2+ but not Mn 2+. On the basis of ionic permeabilities and the effect of various blocking agents, there appear to be two distinct passive influx routes. One is permeable to Ca 2+ and Ba 2+ and is blocked by econazole or SKF 96365. The other is permeable to Mn 2+ and is blocked by Ni 2+. There also appear to be two different routes of divalent cation entry involved in responses to receptor activation. One allows both Ba 2+ and Ca 2+ to enter and is blocked by Ni 2+. The other allows only Ca 2+ to enter and is blocked by U73122 and may therefore involve the activation of phospholipase C.

A 16 kDa protein substrate for protein kinase C and its phosphorylation upon stimulation of vasopressin receptors in rat aortic myocytes

Phosphorylation induced by protein kinase C was examined in a plasma membrane fraction from rat aortic myocytes. Labelled phosphate incorporation produced by addition of kinase C to the membrane preparation allowed to identify a 16 kDa protein as the major substrate of the enzyme. This protein electrophoretically migrated with a protein phosphorylated by cAMP dependent protein kinase, but the two kinases produced phosphorylation of different sites since their effects were additive. Pretreatment of the myocytes with a kinase C activating phorbol ester or with vasopressin decreased further phosphate incorporation into the 16 kDa protein under the influence of exogenous kinase C. The results provide evidence that vasopressin produced in situ phosphorylation of the 16 kDa protein in rat aortic myocytes, with a time course and at concentrations consistent with a role of kinase C activation in the response of aortic myocytes to stimulation of V 1 receptors.