Angiotensin II inhibits native bTREK-1 K+ channels through a PLC-, kinase C-, and PIP2-independent pathway requiring ATP hydrolysis

2007 ◽  
Vol 293 (2) ◽  
pp. C682-C695 ◽  
Author(s):  
Haiyan Liu ◽  
Judith A. Enyeart ◽  
John J. Enyeart
Keyword(s):  
Angiotensin Ii ◽  
Atp Hydrolysis ◽  
Water Soluble ◽  
Zona Fasciculata ◽  
Ang Ii ◽  
Patch Clamp Recording ◽  
Adrenocortical Cells ◽  
Signaling Mechanism ◽  
Pipette Solution ◽  
Dependent Inhibition

Angiotensin II (ANG II) inhibits bTREK-1 (bovine KCNK2) K+ channels in bovine adrenocortical cells through a Gq-coupled AT1 receptor by activation of separate Ca2+- and ATP hydrolysis-dependent signaling pathways. Whole cell patch-clamp recording from bovine adrenal zona fasciculata (AZF) cells was used to characterize the ATP-dependent signaling mechanism for inhibition of bTREK-1 by ANG II. We discovered that ATP-dependent inhibition of bTREK-1 by ANG II occurred through a novel mechanism that was independent of PLC and its established downstream effectors. The ATP-dependent inhibition of bTREK-1 by ANG II was not reduced by the PLC antagonists edelfosine and U73122, or by the PKC antagonists bisindolylmaleimide I (BIM) or calphostin C. bTREK-1 was partially inhibited (∼25%) by the PKC activator phorbol 12,13 dibutyrate (PDBu) through an ATP-dependent mechanism that was blocked by BIM. Addition of Phosphatidylinositol( 4 , 5 ) bisphosphate diC8 [DiC8PI( 4 , 5 )P2], a water-soluble derivative of phosphotidyl inositol 4,5 bisphosphate (PIP2) to the pipette solution failed to alter inhibition by ANG II. bTREK-1 inhibition by ANG II was also insensitive to antagonists of other protein kinases activated by ANG II in adrenocortical cells but was completely blocked by inorganic polytriphosphate PPPi. DiC8PI( 4 , 5 )P2 was a weak activator of bTREK-1 channels, compared with the high-affinity ATP analog N6-(2-phenylethyl)adenosine-5′-O-triphosphate (6-PhEt-ATP). These results demonstrate that the modulation of bTREK-1 channels in bovine AZF cells is distinctive with respect to activation by phosphoinositides and nucleotides and inhibition by Gq-coupled receptors. Importantly, ANG II inhibits bTREK-1 channels through a novel pathway that is different from that described for inhibition of native TREK-1 channels in neurons, or cloned channels expressed in cell lines. They also indicate that, under physiological conditions, ANG II inhibits bTREK-1 and depolarizes AZF cells by two, novel, independent pathways that diverge proximal to the activation of PLC.

scholarly journals Calcium-dependent inhibition of adrenal TREK-1 channels by angiotensin II and ionomycin

2011 ◽  
Vol 301 (3) ◽  
pp. C619-C629 ◽  
Author(s):  
John J. Enyeart ◽  
Haiyan Liu ◽  
Judith A. Enyeart
Keyword(s):  
Atp Hydrolysis ◽  
Water Soluble ◽  
Zona Fasciculata ◽  
Dependent Manner ◽  
Ang Ii ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
Concentration Dependent Manner ◽  
Whole Cell ◽  
Dependent Inhibition

Bovine adrenocortical cells express bTREK-1 K+ (bovine KCNK2) channels that are inhibited by ANG II through a Gq-coupled receptor by separate Ca2+ and ATP hydrolysis-dependent signaling pathways. Whole cell and single patch clamp recording from adrenal zona fasciculata (AZF) cells were used to characterize Ca2+-dependent inhibition of bTREK-1. In whole cell recordings with pipette solutions containing 0.5 mM EGTA and no ATP, the Ca2+ ionophore ionomycin (1 μM) produced a transient inhibition of bTREK-1 that reversed spontaneously within minutes. At higher concentrations, ionomycin (5–10 μM) produced a sustained inhibition of bTREK-1 that was reversible upon washing, even in the absence of hydrolyzable [ATP]i. BAPTA was much more effective than EGTA at suppressing bTREK-1 inhibition by ANG II. When intracellular Ca2+ concentration ([Ca2+]i) was buffered to 20 nM with either 11 mM BAPTA or EGTA, ANG II (10 nM) inhibited bTREK-1 by 12.0 ± 4.5% ( n=11) and 59.3 ± 8.4% ( n=4), respectively. Inclusion of the water-soluble phosphatidylinositol 4,5-bisphosphate (PIP2) analog DiC8PI(4,5)P2 in the pipette failed to increase bTREK-1 expression or reduce its inhibition by ANG II. The open probability ( Po) of unitary bTREK-1 channels recorded from inside-out patches was reduced by Ca2+ (10–35 μM) in a concentration-dependent manner. These results are consistent with a model in which ANG II inhibits bTREK-1 K+ channels by a Ca2+-dependent mechanism that does not require the depletion of membrane-associated PIP2. They further indicate that the Ca2+ source is located in close proximity within a “Ca2+ nanodomain” of bTREK-1 channels, where [Ca2+]i may reach concentrations of >10 μM. bTREK-1 is the first two-pore K+ channel shown to be inhibited by Ca2+ through activation of a G protein-coupled receptor.

scholarly journals Sodium Tanshinone IIA Sulfonate Prevents Angiotensin II-Induced Differentiation of Human Atrial Fibroblasts into Myofibroblasts

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Tangting Chen ◽  
Miaoling Li ◽  
Xuehui Fan ◽  
Jun Cheng ◽  
Liqun Wang
Keyword(s):  
Angiotensin Ii ◽  
Critical Role ◽  
Water Soluble ◽  
Collagen I ◽  
Tanshinone Iia ◽  
Ang Ii ◽  
Induced Differentiation ◽  
Fibroblast Migration ◽  
Collagen Iii ◽  
Sodium Tanshinone Iia Sulfonate

Differentiation of atrial fibroblasts into myofibroblasts plays a critical role in atrial fibrosis. Sodium tanshinone IIA sulfonate (DS-201), a water-soluble derivative of tanshinone IIA, has been shown to have potent antifibrotic properties. However, the protective effects of DS-201 on angiotensin II- (Ang II-) induced differentiation of atrial fibroblasts into myofibroblasts remain to be elucidated. In this study, human atrial fibroblasts were stimulated with Ang II in the presence or absence of DS-201. Then, α-smooth muscle actin (α-SMA), collagen I, and collagen III expression and reactive oxygen species (ROS) generation were measured. The expression of transforming growth factor-β1 (TGF-β1) and the downstream signaling of TGF-β1, such as phosphorylation of Smad2/3, were also determined. The results demonstrated that DS-201 significantly prevented Ang II-induced human atrial fibroblast migration and decreased Ang II-induced α-SMA, collagen I, and collagen III expression. Furthermore, increased production of ROS and expression of TGF-β1 stimulated by Ang II were also significantly inhibited by DS-201. Consistent with these results, DS-201 significantly inhibited Ang II-evoked Smad2/3 phosphorylation and periostin expression. These results and the experiments involving N-acetyl cysteine (antioxidant) and an anti-TGF-β1 antibody suggest that DS-201 prevent Ang II-induced differentiation of atrial fibroblasts to myofibroblasts, at least in part, through suppressing oxidative stress and inhibiting the activation of TGF-β1 signaling pathway. All of these data indicate the potential utility of DS-201 for the treatment of cardiac fibrosis.

scholarly journals Salvianolic Acid B Attenuates Rat Hepatic Fibrosis via Downregulating Angiotensin II Signaling

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Shu Li ◽  
Lina Wang ◽  
Xiuchuan Yan ◽  
Qinglan Wang ◽  
Yanyan Tao ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Hepatic Fibrosis ◽  
Water Soluble ◽  
Salvianolic Acid B ◽  
Type I ◽  
Ang Ii ◽  
Radix Salviae Miltiorrhizae ◽  
Fibrotic Liver ◽  
Salvianolic Acid

The renin-angiotensin system (RAS) plays an important role in hepatic fibrosis. Salvianolic acid B (Sal B), one of the water-soluble components from Radix Salviae miltiorrhizae, has been used to treat hepatic fibrosis, but it is still not clear whether the effect of Sal B is related to angiotensin II (Ang II) signaling pathway. In the present study, we studied Sal B effect on rat liver fibrosis and Ang-II related signaling mediators in dimethylnitrosamine-(DMN-) induced rat fibrotic modelin vivoand Ang-II stimulated hepatic stellate cells (HSCs)in vitro, with perindopril or losartan as control drug, respectively. The results showed that Sal B and perindopril inhibited rat hepatic fibrosis and reduced expression of Ang II receptor type 1 (AT1R) and ERK activation in fibrotic liver. Sal B and losartan also inhibited Ang II-stimulated HSC activation including cell proliferation and expression of type I collagen I (Col-I) andα-smooth muscle actin (α-SMA) productionin vitro, reduced the gene expression of transforming growth factor beta (TGF-β), and downregulated AT1R expression and ERK and c-Jun phosphorylation. In conclusion, our results indicate that Sal B may exert an antihepatic fibrosis effect via downregulating Ang II signaling in HSC activation.

Effects of angiotensin II and ACTH on normal and tumourous human adrenocortical cells

1983 ◽  
Vol 104 (1) ◽  
pp. 103-109 ◽  
Author(s):  
Wolfgang Belmega ◽  
Wolfgang Oelkers ◽  
Lutz Belkien ◽  
Monika Shirpai ◽  
Ulrich Fiedler ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Renin Angiotensin System ◽  
Zona Glomerulosa ◽  
Zona Fasciculata ◽  
Adrenocortical Adenoma ◽  
Response Curves ◽  
Adrenocortical Cells ◽  
Normal Cells ◽  
Fold Stimulation

Abstract. Isolated adrenocortical cells from 6 patients with a 'normal' zona fasciculata, 4 patients with a 'normal' zona glomerulosa, and tumour cells from 1 adrenocortical adenoma and 1 carcinoma were incubated with and without increasing concentrations of ACTH 1–24 (10−13 m to 10−9 m) or Asp1-Ile5-angiotensin II (10−11 m to 10−7 m). In 4/5 'normal' cases, cortisol was clearly stimulated by 10−13 m ACTH. The maximum of the dose-response curve (5-fold stimulation) was reached at 10−10 m ACTH. Angiotensin II (All) started to stimulate 'normal' cells at 10−11 m with a maximum (2-fold stimulation) at 10−9 m. Aldosterone production by 'normal' cells was less markedly stimulated by ACTH and All, although the threshold doses for both peptides were similar to those of the cortisol response curves. The cells of the adrenocortical adenoma from a patient with Cushing's syndrome produced large amounts of cortisol and small amounts of aldosterone, both steroids being clearly stimulated by ACTH and AII. The adrenocortical carcinoma cells produced small amounts of cortisol and no aldosterone. Cortisol production responded to ACTH, but not to AII. The results suggest that an activated renin-angiotensin system may stimulate the zona fasciculata, since 10−11 m All (= 10 pg AII/ml) is a normal plasma All concentration on an unrestricted diet. Clinical evidence supporting this thesis is reviewed. However, cortisol production itself will rarely be increased by All in vivo, since a downregulation of ACTH would occur.

Effects of angiotensin II on proximal tubular cells stably transfected with the c-mas oncogene

1992 ◽  
Vol 263 (5) ◽  
pp. F931-F938 ◽  
Author(s):  
G. Wolf ◽  
E. G. Neilson
Keyword(s):  
Angiotensin Ii ◽  
De Novo ◽  
Cell Phenotype ◽  
Scatchard Analysis ◽  
Tubular Epithelium ◽  
Ang Ii ◽  
Protein Signaling ◽  
Signaling Mechanism ◽  
Cellular Hypertrophy ◽  
Proximal Tubular

Angiotensin II (ANG II) normally induces cellular hypertrophy in proximal tubular epithelium by engaging receptor systems that use a G-protein-signaling mechanism. The c-mas oncogene also encodes part of a superfamily of vasoactive peptide receptor-like moieties that couple to G proteins. To determine whether the stable expression of the c-mas gene might alter or modify the induction of cellular hypertrophy by ANG II in tubular epithelium, a rat c-mas cDNA was cloned into the pSV2 expression vector for use in cell transfection. Scatchard analysis of ANG II binding revealed no significant differences in ANG II receptor number or in the dissociation constant between pSV2mas-transfected or wild-type MCT cells, but rather an increase in the number of receptors not replaceable by known inhibitors. ANG II also induced proliferation in pSV2mas-transfected MCT cells that was not blocked by conventional inhibitors and increased intracellular levels of inositol trisphosphate. ANG II, furthermore, did not increase de novo protein synthesis in pSV2-transfected MCT cells and failed to lower their intracellular concentration of adenosine 3',5'-cyclic monophosphate, both expected parameters of cellular hypertrophy. Our findings demonstrate that expression of c-mas in tubular epithelium can modulate tubular cell phenotype toward proliferation rather than hypertrophy. This effect is likely mediated by a reshuffling of the heterogeneity of ANG II receptors on the cell surface, or perhaps by the emergence of a new ANG II receptor, followed by alterations in the process of signal transduction.

scholarly journals B-Type Natriuretic Peptide Inhibited Angiotensin II-Stimulated Cholesterol Biosynthesis, Cholesterol Transfer, and Steroidogenesis in Primary Human Adrenocortical Cells

Endocrinology ◽  
2007 ◽  
Vol 148 (8) ◽  
pp. 3722-3729 ◽  
Author(s):  
Faquan Liang ◽  
Ann M. Kapoun ◽  
Andrew Lam ◽  
Debby L. Damm ◽  
Diana Quan ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Mitochondrial Membrane ◽  
Coenzyme A ◽  
Cholesterol Biosynthesis ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Ang Ii ◽  
Inner Mitochondrial Membrane ◽  
Adrenocortical Cells

In this study, we demonstrate that B-type natriuretic peptide (BNP) opposed angiotensin II (Ang II)-stimulated de novo cholesterol biosynthesis, cellular cholesterol uptake, cholesterol transfer to the inner mitochondrial membrane, and steroidogenesis, which are required for biosynthesis of steroid hormones such as aldosterone and cortisol in primary human adrenocortical cells. BNP dose-dependently stimulated intracellular cGMP production with an EC50 of 11 nm, implying that human adrenocortical cells express the guanylyl cyclase A receptor. cDNA microarray and real-time RT-PCR analyses revealed that BNP inhibited Ang II-stimulated genes related to cholesterol biosynthesis (acetoacetyl coenzyme A thiolase, HMG coenzyme A synthase 1, HMG coenzyme A reductase, isopentenyl-diphosphate Δ-isomerase, lanosterol synthase, sterol-4C-methyl oxidase, and emopamil binding protein/sterol isomerase), cholesterol uptake from circulating lipoproteins (scavenger receptor class B type I and low-density lipoprotein receptor), cholesterol transfer to the inner mitochondrial membrane (steroidogenic acute regulatory protein), and steroidogenesis (ferredoxin 1,3β-hydroxysteroid dehydrogenase, glutathione transferase A3, CYP19A1, CYP11B1, and CYP11B2). Consistent with the microarray and real-time PCR results, BNP also blocked Ang II-induced binding of 125I-labeled low-density lipoprotein and 125I-labeled high-density lipoprotein to human adrenocortical cells. Furthermore, BNP markedly inhibited Ang II-stimulated release of estradiol, aldosterone, and cortisol from cultured primary human adrenocortical cells. These findings demonstrate that BNP opposes Ang II-induced steroidogenesis via multiple steps from cholesterol supply and transfer to the final formation of steroid hormones. This study provides new insights into the cellular mechanisms by which BNP modulates Ang II-induced steroidogenesis in the adrenal gland.

scholarly journals Angiotensin II stimulates epithelial sodium channels in the cortical collecting duct of the rat kidney

2012 ◽  
Vol 302 (6) ◽  
pp. F679-F687 ◽  
Author(s):  
Peng Sun ◽  
Peng Yue ◽  
Wen-Hui Wang
Keyword(s):  
Angiotensin Ii ◽  
Single Channel ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Ang Ii ◽  
Cortical Collecting Duct ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
Whole Cell ◽  
Na Currents

We examined the effect of angiotensin II (ANG II) on epithelial Na+channel (ENaC) in the rat cortical collecting duct (CCD) with single-channel and the perforated whole cell patch-clamp recording. Application of 50 nM ANG II increased ENaC activity, defined by NPo(a product of channel numbers and open probability), and the amiloride-sensitive whole cell Na currents by twofold. The stimulatory effect of ANG II on ENaC was absent in the presence of losartan, suggesting that the effect of ANG II on ENaC was mediated by ANG II type 1 receptor. Moreover, depletion of intracellular Ca2+with 1,2-bis(2-aminophenoxy)ethane- N, N, N′, N′-tetraacetic acid (BAPTA)-AM failed to abolish the stimulatory effect of ANG II on ENaC but inhibiting protein kinase C (PKC) abolished the effect of ANG II, suggesting that the effect of ANG II was the result of stimulating Ca2+-independent PKC. This notion was also suggested by the experiments in which stimulation of PKC with phorbol ester derivative mimicked the effect of ANG II and increased amiloride-sensitive Na currents in the principal cell, an effect that was not abolished by treatment of the CCD with BAPTA-AM. Also, inhibition of NADPH oxidase (NOX) with diphenyleneiodonium chloride abolished the stimulatory effect of ANG II on ENaC and application of superoxide donors, pyrogallol or xanthine and xanthine oxidase, significantly increased ENaC activity. Moreover, addition of ANG II or H2O2diminished the arachidonic acid (AA)-induced inhibition of ENaC in the CCD. We conclude that ANG II stimulates ENaC in the CCD through a Ca2+-independent PKC pathway that activates NOX thereby increasing superoxide generation. The stimulatory effect of ANG II on ENaC may be partially the result of blocking AA-induced inhibition of ENaC.

scholarly journals Aldosterone Breakthrough Caused by Chronic Blockage of Angiotensin II Type 1 Receptors in Human Adrenocortical Cells: Possible Involvement of Bone Morphogenetic Protein-6 Actions

Endocrinology ◽  
2008 ◽  
Vol 149 (6) ◽  
pp. 2816-2825 ◽  
Author(s):  
Hiroyuki Otani ◽  
Fumio Otsuka ◽  
Kenichi Inagaki ◽  
Jiro Suzuki ◽  
Tomoko Miyoshi ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Bone Morphogenetic Protein ◽  
Ang Ii ◽  
Adrenocortical Cells ◽  
Activin Receptor ◽  
Morphogenetic Protein ◽  
Receptor Like Kinase ◽  
Aldosterone Production ◽  
Aldosterone Breakthrough

Circulating aldosterone concentrations occasionally increase after initial suppression with angiotensin II (Ang II) converting enzyme inhibitors or Ang II type 1 receptor blockers (ARBs), a phenomenon referred to as aldosterone breakthrough. However, the underlying mechanism causing the aldosterone breakthrough remains unknown. Here we investigated whether aldosterone breakthrough occurs in human adrenocortical H295R cells in vitro. We recently reported that bone morphogenetic protein (BMP)-6, which is expressed in adrenocortical cells, enhances Ang II- but not potassium-induced aldosterone production in human adrenocortical cells. Accordingly, we examined the roles of BMP-6 in aldosterone breakthrough induced by long-term treatment with ARB. Ang II stimulated aldosterone production by adrenocortical cells. This Ang II stimulation was blocked by an ARB, candesartan. Interestingly, the candesartan effects on Ang II-induced aldosterone synthesis and CYP11B2 expression were attenuated in a course of candesartan treatment for 15 d. The impairment of candesartan effects on Ang II-induced aldosterone production was also observed in Ang II- or candesartan-pretreated cells. Levels of Ang II type 1 receptor mRNA were not changed by chronic candesartan treatment. However, BMP-6 enhancement of Ang II-induced ERK1/2 signaling was resistant to candesartan. The BMP-6-induced Smad1, -5, and -8 phosphorylation, and BRE-Luc activity was augmented in the presence of Ang II and candesartan in the chronic phase. Chronic Ang II exposure decreased cellular expression levels of BMP-6 and its receptors activin receptor-like kinase-2 and activin type II receptor mRNAs. Cotreatment with candesartan reversed the inhibitory effects of Ang II on the expression levels of these mRNAs. The breakthrough phenomenon was attenuated by neutralization of endogenous BMP-6 and activin receptor-like kinase-2. Collectively, these data suggest that changes in BMP-6 availability and response may be involved in the occurrence of cellular escape from aldosterone suppression under chronic treatment with ARB.

scholarly journals Angiotensin-II modulates GABAergic neurotransmission in the mouse substantia nigra

2021 ◽  
Author(s):  
Maibam R. Singh ◽  
Jozsef Vigh ◽  
Gregory C. Amberg
Keyword(s):  
Angiotensin Ii ◽  
Basal Ganglia ◽  
Substantia Nigra ◽  
Neuronal Activity ◽  
Dopaminergic Neurons ◽  
Gabaergic Neurons ◽  
Inhibitory Input ◽  
Ang Ii ◽  
Signaling Mechanism ◽  
Gabaergic Neurotransmission

ABSTRACTGABAergic projections neurons of the substantia nigra reticulata (SNr), through an extensive network of dendritic arbors and axon collaterals, provide robust inhibitory input to neighboring dopaminergic neurons in the substantia nigra compacta (SNc). Angiotensin-II (Ang-II) receptor signaling increases SNc dopaminergic neuronal sensitivity to insult, thus rendering these cells susceptible to dysfunction and destruction. However, the mechanisms by which Ang-II regulates SNc dopaminergic neuronal activity are unclear. Given the complex relationship between SN dopaminergic and GABAergic neurons, we hypothesized that Ang-II could regulate SNc dopaminergic neuronal activity directly and indirectly by modulating SNr GABAergic neurotransmission. Herein, using transgenic mice, slice electrophysiology, and optogenetics, we provide evidence of an AT1 receptor-mediated signaling mechanism in SNr GABAergic neurons where Ang-II suppresses electrically-evoked neuronal output by facilitating postsynaptic GABAA receptors and prolonging the action potential duration. Unexpectedly, Ang-II had no discernable effects on the electrical properties of SNc dopaminergic neurons. Also, and indicating a nonlinear relationship between electrical activity and neuronal output, following phasic photoactivation of SNr GABAergic neurons, Ang-II paradoxically enhanced the feedforward inhibitory input to SNc dopaminergic neurons. In sum, our observations describe an increasingly complex and heterogeneous response of the SN to Ang-II by revealing cell-specific responses and nonlinear effects on intranigral GABAergic neurotransmission. Our data further implicate the renin-angiotensin-system as a functionally relevant neuromodulator in the basal ganglia, thus underscoring a need for additional inquiry.SIGNIFICANCE STATEMENTAngiotensin II (Ang-II) promotes dopamine release in the striatum and, in the substantia nigra compacta (SNc), exacerbates dopaminergic cell loss in animal models of Parkinson’s disease. Despite a potential association with Parkinson’s disease, the effects of Ang-II on neuronal activity in the basal ganglia is unknown. Here we describe a novel AT1 receptor-dependent signaling mechanism in GABAergic projection neurons of the SN reticulata (SNr), a major inhibitory regulator of SNc dopaminergic neurons. Specifically, Ang-II suppresses SNr GABAergic neuronal activity, subsequently altering GABAergic modulation of SNc dopaminergic neurons in a nonlinear fashion. Altogether, our data provide the first indication of Ang-II-dependent modulation of GABAergic neurotransmission in the SN, which could impact output from the basal ganglia in health and disease.

TREK-1 K+ channels couple angiotensin II receptors to membrane depolarization and aldosterone secretion in bovine adrenal glomerulosa cells

2004 ◽  
Vol 287 (6) ◽  
pp. E1154-E1165 ◽  
Author(s):  
Judith A. Enyeart ◽  
Sanjay J. Danthi ◽  
John J. Enyeart
Keyword(s):  
Membrane Potential ◽  
Angiotensin Ii ◽  
Adrenal Cortex ◽  
Receptor Activation ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Zona Fasciculata ◽  
Ang Ii ◽  
Aldosterone Secretion ◽  
Wide Range

Bovine adrenal glomerulosa (AZG) cells were shown to express bTREK-1 background K+ channels that set the resting membrane potential and couple angiotensin II (ANG II) receptor activation to membrane depolarization and aldosterone secretion. Northern blot and in situ hybridization studies demonstrated that bTREK-1 mRNA is uniformly distributed in the bovine adrenal cortex, including zona fasciculata and zona glomerulosa, but is absent from the medulla. TASK-3 mRNA, which codes for the predominant background K+ channel in rat AZG cells, is undetectable in the bovine adrenal cortex. In whole cell voltage clamp recordings, bovine AZG cells express a rapidly inactivating voltage-gated K+ current and a noninactivating background K+ current with properties that collectively identify it as bTREK-1. The outwardly rectifying K+ current was activated by intracellular acidification, ATP, and superfusion of bTREK-1 openers, including arachidonic acid (AA) and cinnamyl 1–3,4-dihydroxy-α-cyanocinnamate (CDC). Bovine chromaffin cells did not express this current. In voltage and current clamp recordings, ANG II (10 nM) selectively inhibited the noninactivating K+ current by 82.1 ± 6.1% and depolarized AZG cells by 31.6 ± 2.3 mV. CDC and AA overwhelmed ANG II-mediated inhibition of bTREK-1 and restored the resting membrane potential to its control value even in the continued presence of ANG II. Vasopressin (50 nM), which also physiologically stimulates aldosterone secretion, inhibited the background K+ current by 73.8 ± 9.4%. In contrast to its potent inhibition of bTREK-1, ANG II failed to alter the T-type Ca2+ current measured over a wide range of test potentials by using pipette solutions of identical nucleotide and Ca2+-buffering compositions. ANG II also failed to alter the voltage dependence of T channel activation under these same conditions. Overall, these results identify bTREK-1 K+ channels as a pivotal control point where ANG II receptor activation is transduced to depolarization-dependent Ca2+ entry and aldosterone secretion.

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