Human Adrenal Glomerulosa Cells Express K2P and GIRK Potassium Channels that are inhibited by AngII and ACTH

2021 ◽  
Author(s):  
John J. Enyeart ◽  
Judith A. Enyeart
Keyword(s):  
G Protein ◽  
Zona Glomerulosa ◽  
Time Dependent ◽  
Aldosterone Secretion ◽  
Girk Channels ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Girk Channel ◽  
Inwardly Rectifying ◽  
G Protein Coupled

In whole-cell patch clamp recordings, it was discovered that normal human adrenal zona glomerulosa (AZG) cells express members of the three major families of K+ channels. Among these are a two pore (K2P) leak-type and a G-protein-coupled, inwardly-rectifying (GIRK) channel, both inhibited by peptide hormones that stimulate aldosterone secretion. The K2P current displayed properties identifying it as TREK-1 (KCNK2). This outwardly-rectifying current was activated by arachidonic acid and inhibited by angiotensin II (AngII), adrenocorticotrophic hormone (ACTH), and forskolin. The activation and inhibition of TREK-1 was coupled to AZG cell hyperpolarization and depolarization, respectively. A second K2P channel, TASK-1 (KCNK3), was expressed at a lower density in AZG cells. Human AZG cells also express inwardly rectifying K+ current(s) (KIR) that include quasi-instantaneous and time-dependent components. This is the first report demonstrating the presence of KIR in whole cell recordings from AZG cells of any species. The time-dependent current was selectively inhibited by AngII, and ACTH, identifying it as a G protein-coupled (GIRK) channel, most likely KIR3.4 (KCNJ5). The quasi-instantaneous KIR current was not inhibited by AngII or ACTH, and may be a separate non-GIRK current. Finally, AZG cells express a voltage-gated, rapidly inactivating K+ current whose properties identified as KV1.4 (KCNA4), a conclusion confirmed by Northern blot. These findings demonstrate that human AZG cells express K2P and GIRK channels whose inhibition by AngII and ACTH are likely coupled to depolarization-dependent secretion. They further demonstrate that human AZG K+ channels differ fundamentally from the widely adopted rodent models for human aldosterone secretion.

scholarly journals Suprachiasmatic nucleus function and circadian entrainment are modulated by G protein‐coupled inwardly rectifying (GIRK) channels

2014 ◽  
Vol 592 (22) ◽  
pp. 5079-5092 ◽  
Author(s):  
L. M. Hablitz ◽  
H. E. Molzof ◽  
J. R. Paul ◽  
R. L. Johnson ◽  
K. L. Gamble
Keyword(s):  
G Protein ◽  
Suprachiasmatic Nucleus ◽  
Girk Channels ◽  
Inwardly Rectifying ◽  
G Protein Coupled

Differential Effects of General Anesthetics on G Protein–coupled Inwardly Rectifying and Other Potassium Channels

2001 ◽  
Vol 95 (1) ◽  
pp. 144-153 ◽  
Author(s):  
Tomohiro Yamakura ◽  
Joanne M. Lewohl ◽  
R. Adron Harris
Keyword(s):  
Nitrous Oxide ◽  
Potassium Channels ◽  
G Protein ◽  
Volatile Anesthetics ◽  
General Anesthetics ◽  
Girk Channels ◽  
Intravenous Anesthetics ◽  
Amino Acid Mutations ◽  
Inwardly Rectifying ◽  
G Protein Coupled

Background General anesthetics differentially affect various families of potassium channels, and some potassium channels are suggested to be potential targets for anesthetics and alcohols. Methods The voltage-gated (ERG1, ELK1, and KCNQ2/3) and inwardly rectifying (GIRK1/2, GIRK1/4, GIRK2, IRK1, and ROMK1) potassium channels were expressed in Xenopus oocytes. Effects of volatile agents [halothane, isoflurane, enflurane, F3 (1-chloro-1,2,2-trifluorocyclobutane), and the structurally related nonimmobilizer F6 (1,2-dichlorohexafluorocyclobutane)], as well as intravenous (pentobarbital, propofol, etomidate, alphaxalone, ketamine), and gaseous (nitrous oxide) anesthetics and alcohols (ethanol and hexanol) on channel function were studied using a two-electrode voltage clamp. Results ERG1, ELK1, and KCNQ2/3 channels were either inhibited slightly or unaffected by concentrations corresponding to twice the minimum alveolar concentrations or twice the anesthetic EC50 of volatile and intravenous anesthetics and alcohols. In contrast, G protein-coupled inwardly rectifying potassium (GIRK) channels were inhibited by volatile anesthetics but not by intravenous anesthetics. The neuronal-type GIRK1/2 channels were inhibited by 2 minimum alveolar concentrations of halothane or F3 by 45 and 81%, respectively, whereas the cardiac-type GIRK1/4 channels were inhibited only by F3. Conversely, IRK1 and ROMK1 channels were completely resistant to all anesthetics tested. Current responses of GIRK2 channels activated by mu-opioid receptors were also inhibited by halothane. Nitrous oxide (approximately 0.6 atmosphere) slightly but selectively potentiated GIRK channels. Results of chimeric and multiple amino acid mutations suggest that the region containing the transmembrane domains, but not the pore-forming domain, may be involved in determining differences in anesthetic sensitivity between GIRK and IRK channels. Conclusions G protein-coupled inwardly rectifying potassium channels, especially those composed of GIRK2 subunits, were inhibited by clinical concentrations of volatile anesthetics. This action may be related to some side effects of these agents.

Abstract 17317: Differential Coupling and Regulation of GIRK-Dependent Muscarinic and Adenosine Receptor Signaling in Mouse Sino-Atrial Nodal Cells

Circulation ◽  
2018 ◽  
Vol 138 (Suppl_1) ◽  
Author(s):  
Allison Anderson ◽  
Kevin Wickman
Keyword(s):  
G Protein ◽  
Adenosine Receptor ◽  
Protein Signaling ◽  
Wild Type ◽  
Girk Channels ◽  
Genetic Ablation ◽  
Whole Cell Patch Clamp ◽  
Girk Channel ◽  
Induced Currents ◽  
Patch Clamp Electrophysiology

Introduction and Hypothesis: Parasympathetic slowing of heart rate is largely mediated by muscarinic receptor (M2R) activation of the G protein gated inwardly-rectifying potassium (GIRK) channel on sinoatrial-nodal (SAN) cells and atrial myocytes. The strength of M2R-GIRK signaling is negatively regulated by regulator of G protein signaling 6, RGS6. Genetic ablation of RGS6 in mice gives rise to enhanced M2R-GIRK signaling in SAN cells, resulting in both exaggerated M2R-induced bradycardia and increased susceptibility to pacing-induced atrial fibrillation. Adenosine receptor (A1R) activation, which can provoke atrial arrhythmias in human patients, can also activate GIRK channels, however, the details of A1R-GIRK signaling are poorly understood. Here, we investigated A1R-GIRK signaling in mouse SAN cells and tested the hypothesis that RGS6 negatively regulates A1R-GIRK signaling. Methods and Results: Using whole-cell patch-clamp electrophysiology, we measured the efficacy and potency of M2R- and A1R- GIRK signaling in adult SAN cells from wildtype and Rgs6 -/- mice. We found SAN cells from Rgs6 -/- mice displayed both prolonged channel deactivation kinetics and increased channel sensitivity to CCh-induced currents as compared to wild-type SAN cells. Surprisingly, we found no difference in kinetics or channel sensitivity of A1R-GIRK responses in Rgs6 -/- SAN cells. We did observe, however, a striking, significant increase in the amplitude of the A1R-GIRK response in Rgs6 -/- SAN cells compared to wild-type controls. Furthermore, occlusion studies in wild-type SAN cells suggest that M2R activates nearly all of the GIRK channels present in SAN cells, while A1R activation results in only partial GIRK channel activation. Intriguingly, RGS6 ablation seems to allow a larger proportion of GIRK channels to be activated by A1R. Recordings from mice lacking cardiac GIRK channels confirm that M2R- and A1R- induced currents are GIRK-dependent. Conclusions: Our results suggest that M2R-GIRK and A1R-GIRK are coupled differently within mouse sino-atrial nodal cells, resulting in differential regulation by RGS6.

Sign Inversion in Photopharmacology: Incorporation of Cyclic Azobenzenes in Photoswitchable Potassium Channel Blockers and Openers

2019 ◽  
Author(s):  
Julie Trads ◽  
Katharina Hüll ◽  
Bryan Matsuura ◽  
Laura Laprell ◽  
Timm Fehrentz ◽  
...  
Keyword(s):  
G Protein ◽  
Biologically Active ◽  
Channel Blockers ◽  
Biological Applications ◽  
Girk Channels ◽  
Voltage Gated ◽  
Sign Inversion ◽  
Potassium Channel Blockers ◽  
Inwardly Rectifying ◽  
G Protein Coupled

Photopharmacology relies on ligands that change their pharmacodynamics upon photoisomerization. Many of these ligands are azobenzenes that are thermodynamically more stable in their elongated <i>trans</i>configuration, which predominates in the dark. Often, they are biologically active in this form and lose activity upon irradiation and photoisomerization to their <i>cis</i>-isomer. Recently, cyclic azobenzenes, so-called diazocines, have emerged. They are thermodynamically more stable in their bent <i>cis</i>­‑form than in their elongated <i>trans</i>-form. Incorporation of these switches into a variety of photopharmaceuticals could convert dark-active ligands into dark-inactive ligands, which is preferred in most biological applications. This “pharmacological sign-inversion” is demonstrated for a photochromic blocker of voltage-gated potassium channels, termed <b>CAL</b>, and a photochromic opener of G-protein-coupled inwardly rectifying potassium (GIRK) channels, termed <b>CLOGO</b>.<br>

scholarly journals Differential effects of inhibitory G protein isoforms on G protein-gated inwardly rectifying K+ currents in adult murine atria

2018 ◽  
Vol 314 (5) ◽  
pp. C616-C626 ◽  
Author(s):  
Muriel Nobles ◽  
David Montaigne ◽  
Sonia Sebastian ◽  
Lutz Birnbaumer ◽  
Andrew Tinker
Keyword(s):  
G Protein ◽  
Knockout Mice ◽  
Protein Isoforms ◽  
Girk Channels ◽  
Differential Effects ◽  
Girk Channel ◽  
Inhibitory G Protein ◽  
Genetic Deletion ◽  
The Right ◽  
Inwardly Rectifying

G protein-gated inwardly rectifying K+ (GIRK) channels are the major inwardly rectifying K+ currents in cardiac atrial myocytes and an important determinant of atrial electrophysiology. Inhibitory G protein α-subunits can both mediate activation via acetylcholine but can also suppress basal currents in the absence of agonist. We studied this phenomenon using whole cell patch clamping in murine atria from mice with global genetic deletion of Gαi2, combined deletion of Gαi1/Gαi3, and littermate controls. We found that mice with deletion of Gαi2 had increased basal and agonist-activated currents, particularly in the right atria while in contrast those with Gαi1/Gαi3 deletion had reduced currents. Mice with global genetic deletion of Gαi2 had decreased action potential duration. Tissue preparations of the left atria studied with a multielectrode array from Gαi2 knockout mice showed a shorter effective refractory period, with no change in conduction velocity, than littermate controls. Transcriptional studies revealed increased expression of GIRK channel subunit genes in Gαi2 knockout mice. Thus different G protein isoforms have differential effects on GIRK channel behavior and paradoxically Gαi2 act to increase basal and agonist-activated GIRK currents. Deletion of Gαi2 is potentially proarrhythmic in the atria.

scholarly journals Basal G-protein-gated inwardly rectifying potassium (Kir3/GirK) channels activity governs synaptic plasticity that supports dorsal hippocampus-dependent cognitive functions

2020 ◽  
Author(s):  
Sara Temprano-Carazo ◽  
Souhail Djebari ◽  
Guillermo Iborra-Lazaro ◽  
Irene Sanchez-Rodriguez ◽  
Mauricio O. Nava-Mesa ◽  
...  
Keyword(s):  
Synaptic Plasticity ◽  
Learning And Memory ◽  
G Protein ◽  
Cognitive Functions ◽  
Dorsal Hippocampus ◽  
Hippocampal Slices ◽  
Girk Channels ◽  
Neural Excitability ◽  
Girk Channel ◽  
Inwardly Rectifying

G-protein-gated inwardly rectifying potassium (Kir3/GirK) channel is the effector of many G-protein-coupled receptors. Its dysfunction has been linked to the pathophysiology of Down syndrome, Alzheimer and Parkinson diseases, psychiatric disorders, epilepsy, drug addiction, or alcoholism. GirK channels are constitutively activated in the dorsal hippocampus contributing to resting membrane potential, and their synaptic activation compensates any excitation excess. Here, in order to elucidate the role of GirK channels activity in the maintenance of dorsal hippocampus-dependent cognitive functions, their involvement in controlling neuronal excitability at different levels of complexity was examined. For that purpose, basal GirK activity was pharmacologically modulated by two specific drugs: ML297, a GirK channel opener, and Tertiapin-Q, a GirK channel blocker. Ex vivo, using dorsal hippocampal slices, we studied pharmacological GirK modulation effect on synaptic plasticity processes induced in CA1 by Schaffer collateral stimulation. In vivo, we performed acute intracerebroventricular injections of both GirK modulators to study their contribution to CA3-CA1 synapse electrophysiological properties, synaptic plasticity, and learning and memory capabilities during hippocampal dependent tasks. We found that pharmacological disruption of basal GirK activity in dorsal hippocampus, causing either function gain or loss, induced learning and memory deficits by a mechanism involving neural excitability impairments and alterations in induction and maintenance of long-term synaptic plasticity processes. These results support the contention that an accurate control of GirK activity must take place in the hippocampus to sustain cognitive functions. Significance Statement: The dorsal hippocampus mostly performs cognitive functions related to contextual/spatial associations. These functions rely on synaptic plasticity processes that are critically ruled by a finely tuned neural excitability. Being the downstream physiological effectors of a variety of G-coupled receptors, activation of G protein-gated inwardly rectifying K+ (GirK) channels induces neurons to hyperpolarize, contributing to neural excitability throughout the control of excitatory excess. Here, we demonstrate that modulation of basal GirK channels activity, causing either function gain or loss, transforms HFS-induced LTP into LTD, inducing deficits in dorsal hippocampus-dependent learning and memory. Together, our data show a crucial GirK activity-mediated mechanism that governs synaptic plasticity direction and modulates subsequent hippocampal-dependent cognitive functions.

Role of G protein–gated inwardly rectifying potassium channels in P2Y12 receptor–mediated platelet functional responses

Blood ◽  
2004 ◽  
Vol 104 (5) ◽  
pp. 1335-1343 ◽  
Author(s):  
Haripriya Shankar ◽  
Swaminathan Murugappan ◽  
Soochong Kim ◽  
Jianguo Jin ◽  
Zhongren Ding ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
G Protein ◽  
Shape Change ◽  
Human Platelets ◽  
P2y12 Receptor ◽  
Functional Responses ◽  
Girk Channels ◽  
Girk Channel ◽  
Inwardly Rectifying

Abstract The role of the Gi-coupled platelet P2Y12 receptor in platelet function has been well established. However, the functional effector or effectors contributing directly to αIIbβ3 activation in human platelets has not been delineated. As the P2Y12 receptor has been shown to activate G protein–gated, inwardly rectifying potassium (GIRK) channels, we investigated whether GIRK channels mediate any of the functional responses of the platelet P2Y12 receptor. Western blot analysis revealed that platelets express GIRK1, GIRK2, and GIRK4. In aspirin-treated and washed human platelets, 2 structurally distinct GIRK inhibitors, SCH23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride) and U50488H (trans-(±)-3,4-dichloro-N-methyl-N-[2-(pyrrolidinyl)cyclohexyl] benzeneacetamide methanesulfonate), inhibited adenosine diphosphate (ADP)–, 2-methylthioADP (2-MeSADP)–, U46619-, and low-dose thrombin–mediated platelet aggregation. However, the GIRK channel inhibitors did not affect platelet aggregation induced by high concentrations of thrombin, AYPGKF, or convulxin. Furthermore, the GIRK channel inhibitors reversed SFLLRN-induced platelet aggregation, inhibited the P2Y12-mediated potentiation of dense granule secretion and Akt phosphorylation, and did not affect the agonist-induced Gq-mediated platelet shape change and intracellular calcium mobilization. Unlike AR-C 69931MX, a P2Y12 receptor–selective antagonist, the GIRK channel blockers did not affect the ADP-induced adenlylyl cyclase inhibition, indicating that they do not directly antagonize the P2Y12 receptor. We conclude that GIRK channels are important functional effectors of the P2Y12 receptor in human platelets.

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