scholarly journals Basal and angiotensin II-inhibited neuronal delayed-rectifier K+ current are regulated by thioredoxin

2007 ◽  
Vol 293 (1) ◽  
pp. C211-C217 ◽  
Author(s):  
Tomokazu Matsuura ◽  
Rachael A. Harrison ◽  
Andrew D. Westwell ◽  
Hajime Nakamura ◽  
Anatoly E. Martynyuk ◽  
...  
Keyword(s):  
Neuronal Activity ◽  
Negative Regulator ◽  
General Mechanism ◽  
Delayed Rectifier ◽  
Neuronal Cultures ◽  
Ang Ii ◽  
Small Proteins ◽  
K Current ◽  
Thiol Protein ◽  
Negative Regulatory Role

In previous studies, we determined that macrophage migration inhibitory factor (MIF), acting intracellularly via its intrinsic thiol-protein oxidoreductase (TPOR) activity, stimulates basal neuronal delayed-rectifier K+ current ( IKv) and inhibits basal and angiotensin (ANG) II-induced increases in neuronal activity. These findings are the basis for our hypothesis that MIF is a negative regulator of ANG II actions in neurons. MIF has recently been recategorized as a member of the thioredoxin (Trx) superfamily of small proteins. In the present study we have examined whether Trx influences basal and ANG II-modulated IKv in an effort to determine whether the Trx superfamily can exert a general regulatory influence over neuronal activity and the actions of ANG II. Intracellular application of Trx (0.8–80 nM) into rat hypothalamic/brain stem neurons in culture increased neuronal IKv, as measured by voltage-clamp recordings. This effect of Trx was abolished in the presence of the TPOR inhibitor PMX 464 (800 nM). Furthermore, the mutant protein recombinant human C32S/C35S-Trx, which lacks TPOR activity, failed to alter neuronal IKv. Trx applied at a concentration (0.08 nM) that does not alter basal IKv abolished the inhibition of neuronal IKv produced by ANG II (100 nM). Given our observation that ANG II increases Trx levels in neuronal cultures, it is possible that Trx (like MIF) has a negative regulatory role over basal and ANG II-stimulated neuronal activity via modulation of IKv. Moreover, these data suggest that TPOR may be a general mechanism for negatively regulating neuronal activity.

ANG II-mediated inhibition of neuronal delayed rectifier K+ current: role of protein kinase C-α

2001 ◽  
Vol 281 (1) ◽  
pp. C17-C23 ◽  
Author(s):  
Sheng-Jun Pan ◽  
Mingyan Zhu ◽  
Mohan K. Raizada ◽  
Colin Sumners ◽  
Craig H. Gelband
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Phorbol Esters ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Ang Ii ◽  
Mediated Effects ◽  
Kinase C ◽  
K Current ◽  
Pkc Isozymes

It was previously determined that ANG II and phorbol esters inhibit Kv current in neurons cultured from newborn rat hypothalamus and brain stem in a protein kinase C (PKC)- and Ca2+-dependent manner. Here, we have further defined this signaling pathway by investigating the roles of “physiological” activators of PKC and different PKC isozymes. The cell-permeable PKC activators, diacylglycerol (DAG) analogs 1,2-dioctanoyl- sn-glycerol (1 μmol/l, n = 7) and 1-oleoyl-2-acetyl- sn-glycerol (1 μmol/l, n = 6), mimicked the effect of ANG II and inhibited Kv current. These effects were abolished by the PKC inhibitor chelerythrine (1 μmol/l, n = 5) or by chelation of internal Ca2+ ( n = 8). PKC antisense (AS) oligodeoxynucleotides (2 μmol/l) against Ca2+-dependent PKC isoforms were applied to the neurons to manipulate the endogenous levels of PKC. PKC-α-AS ( n = 4) treatment abolished the inhibitory effects of ANG II and 1-oleoyl-2-acetyl- sn-glycerol on Kv current, whereas PKC-β-AS ( n = 4) and PKC-γ-AS ( n = 4) did not. These results suggest that the angiotensin type 1 receptor-mediated effects of ANG II on neuronal Kv current involve activation of PKC-α.

Chronotropic Effect of Angiotensin II via Type 2 Receptors in Rat Brain Neurons

2001 ◽  
Vol 85 (5) ◽  
pp. 2177-2183 ◽  
Author(s):  
Mingyan Zhu ◽  
Colin Sumners ◽  
Craig H. Gelband ◽  
Philip Posner
Keyword(s):  
Angiotensin Ii ◽  
Firing Rate ◽  
Brain Stem ◽  
Neuronal Firing ◽  
Delayed Rectifier ◽  
Neuronal Cultures ◽  
Ang Ii ◽  
Chronotropic Effect ◽  
Neuronal Firing Rate

Previously, we determined that angiotensin II (Ang II) elicits an Ang II type 2 (AT2) receptor–mediated increase of neuronal delayed rectifier K+( I KV) current in neuronal cultures from newborn rat hypothalamus and brain stem. This requires generation of lipoxygenase (LO) metabolites of arachidonic acid (AA) and activation of serine/threonine phosphatase type 2A (PP-2A). Enhancement of I KV results in a decrease in net inward current during the action potential (AP) upstroke as well as shortening of the refractory period, which may lead to alterations in neuronal firing rate. Thus, in the present study, we used whole-cell current clamp recording methods to investigate the AT2 receptor–mediated effects of Ang II on the firing rate of cultured neurons from the hypothalamus and brain stem. At room temperature, these neurons exhibited spontaneous APs with an amplitude of 77.72 ± 2.7 mV ( n = 20) and they fired at a frequency of 0.8 ± 0.1 Hz ( n = 11). Most cells had a prolonged early after-depolarization that followed an initial fully developed AP. Superfusion of Ang II (100 nM) plus losartan (LOS, 1 μM) to block Ang II type 1 receptors elicited a significant chronotropic effect that was reversed by the AT2 receptor inhibitor PD 123,319 (1 μM). LOS alone had no effect on any of the parameters measured. The chronotropic effect of Ang II was reversed by the general LO inhibitor 5,8,11,14-eicosatetraynoic acid (10 μM) or by the selective PP-2A inhibitor okadaic acid (1 nM) and was mimicked by the 12-LO metabolite of AA 12-(S)-hydroxy-(5Z, 8Z, 10E, 14Z)-eicosatetraynoic acid. These data indicate that Ang II elicits an AT2 receptor–mediated increase in neuronal firing rate, an effect that involves generation of LO metabolites of AA and activation of PP-2A.

Angiotensin II type 2 receptor-modulated changes in potassium currents in cultured neurons

1993 ◽  
Vol 265 (3) ◽  
pp. C607-C616 ◽  
Author(s):  
J. Kang ◽  
C. Sumners ◽  
P. Posner
Keyword(s):  
Angiotensin Ii ◽  
Ionic Current ◽  
Delayed Rectifier ◽  
Receptor Subtype ◽  
Cultured Neurons ◽  
Ang Ii ◽  
Maximal Conductance ◽  
K Current ◽  
At2 Receptors

We have previously shown that angiotensin II (ANG II) stimulates an increase in net outward ionic current (Ino) in neurons cocultured from neonate rat hypothalamus and brain stem, an effect mediated by ANG II type 2 (AT2) receptors. Ino consists mainly of K+ and Ca2+ currents, and in the present study we used whole cell voltage clamp procedures to define which of these currents are modulated by AT2 receptors. We determined that ANG II (50-100 nM) stimulated both transient K+ current (IA) and delayed-rectifier K+ current (IK) in cultured neurons. The effects were mediated by AT2 receptors (blocked by 1 microM PD-123177 but not by 1 microM losartan). For both IA and IK, ANG II elicited an increase in maximal conductance. By contrast, ANG II altered neither Ca(2+)-activated K+ current nor Ca2+ current. Our data demonstrate discrete AT2 receptor-mediated effects of ANG II on IA and IK in cultured neonate neurons. Importantly, these data provide an electrophysiological basis for behavioral or physiological effects (as yet undefined) mediated by this ANG II receptor subtype in the brain.

Modulation of the delayed rectifier K+ current in neurons by an angiotensin II type 2 receptor fragment

1995 ◽  
Vol 268 (1) ◽  
pp. C278-C282 ◽  
Author(s):  
J. Kang ◽  
E. M. Richards ◽  
P. Posner ◽  
C. Sumners
Keyword(s):  
Angiotensin Ii ◽  
Delayed Rectifier ◽  
At2 Receptor ◽  
Ang Ii ◽  
Intracellular Loop ◽  
Pipette Solution ◽  
Random Peptide ◽  
Intracellular Injection ◽  
Gi Protein ◽  
K Current

Angiotensin II (ANG II) stimulates the delayed rectifier K+ current (IK) in neurons cultured from rat hypothalamus and brain stem via AT2 receptors, and this effect involves activation of a Gi protein and protein phosphatase 2A (PP2A). However, there was no evidence that the AT2 receptor involved in this response was the same as the recently cloned AT2 receptor. In the present study, intracellular injection of a 22-amino acid peptide (PEP-22) corresponding to the putative third intracellular loop of the cloned AT2 receptor elicited an increase in IK in cultured neurons that was similar to the effect produced by ANG II. Furthermore, this effect of PEP-22 was abolished by pertussis toxin (200 ng/ml, 24 h) pretreatment and also by superfusion of the PP2A inhibitor okadaic acid (10 nM), suggesting the involvement of Gi protein and PP2A, respectively. Intracellular injection of a random peptide or normal pipette solution did not affect neuronal IK. This is direct evidence to link the cloned AT2 receptor to a defined response elicited by ANG II.

scholarly journals Canine Myocytes Represent a Good Model for Human Ventricular Cells Regarding Their Electrophysiological Properties

2021 ◽  
Vol 14 (8) ◽  
pp. 748
Author(s):  
Péter P. Nánási ◽  
Balázs Horváth ◽  
Fábián Tar ◽  
János Almássy ◽  
Norbert Szentandrássy ◽  
...  
Keyword(s):  
Action Potential ◽  
Time Course ◽  
Laboratory Animals ◽  
Delayed Rectifier ◽  
Ion Currents ◽  
Human Cardiomyocytes ◽  
Ventricular Cells ◽  
Repolarization Reserve ◽  
Electrophysiological Studies ◽  
K Current

Due to the limited availability of healthy human ventricular tissues, the most suitable animal model has to be applied for electrophysiological and pharmacological studies. This can be best identified by studying the properties of ion currents shaping the action potential in the frequently used laboratory animals, such as dogs, rabbits, guinea pigs, or rats, and comparing them to those of human cardiomyocytes. The authors of this article with the experience of three decades of electrophysiological studies, performed in mammalian and human ventricular tissues and isolated cardiomyocytes, summarize their results obtained regarding the major canine and human cardiac ion currents. Accordingly, L-type Ca2+ current (ICa), late Na+ current (INa-late), rapid and slow components of the delayed rectifier K+ current (IKr and IKs, respectively), inward rectifier K+ current (IK1), transient outward K+ current (Ito1), and Na+/Ca2+ exchange current (INCX) were characterized and compared. Importantly, many of these measurements were performed using the action potential voltage clamp technique allowing for visualization of the actual current profiles flowing during the ventricular action potential. Densities and shapes of these ion currents, as well as the action potential configuration, were similar in human and canine ventricular cells, except for the density of IK1 and the recovery kinetics of Ito. IK1 displayed a largely four-fold larger density in canine than human myocytes, and Ito recovery from inactivation displayed a somewhat different time course in the two species. On the basis of these results, it is concluded that canine ventricular cells represent a reasonably good model for human myocytes for electrophysiological studies, however, it must be borne in mind that due to their stronger IK1, the repolarization reserve is more pronounced in canine cells, and moderate differences in the frequency-dependent repolarization patterns can also be anticipated.

scholarly journals Difluoroboron β-diketonate polylactic acid oxygen nanosensors for intracellular neuronal imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Meng Zhuang ◽  
Suchitra Joshi ◽  
Huayu Sun ◽  
Tamal Batabyal ◽  
Cassandra L. Fraser ◽  
...  
Keyword(s):  
Neuronal Activity ◽  
Oxygen Sensing ◽  
Brain Slices ◽  
Neuronal Cell ◽  
Quantum Yields ◽  
Poly Lactic Acid ◽  
Neuronal Cultures ◽  
Primary Neuronal Cultures ◽  
Non Invasive ◽  
Mitotracker Red

AbstractCritical for metabolism, oxygen plays an essential role in maintaining the structure and function of neurons. Oxygen sensing is important in common neurological disorders such as strokes, seizures, or neonatal hypoxic–ischemic injuries, which result from an imbalance between metabolic demand and oxygen supply. Phosphorescence quenching by oxygen provides a non-invasive optical method to measure oxygen levels within cells and tissues. Difluoroboron β-diketonates are a family of luminophores with high quantum yields and tunable fluorescence and phosphorescence when embedded in certain rigid matrices such as poly (lactic acid) (PLA). Boron nanoparticles (BNPs) can be fabricated from dye-PLA materials for oxygen mapping in a variety of biological milieu. These dual-emissive nanoparticles have oxygen-insensitive fluorescence, oxygen-sensitive phosphorescence, and rigid matrix all in one, enabling real-time ratiometric oxygen sensing at micron-level spatial and millisecond-level temporal resolution. In this study, BNPs are applied in mouse brain slices to investigate oxygen distributions and neuronal activity. The optical properties and physical stability of BNPs in a biologically relevant buffer were stable. Primary neuronal cultures were labeled by BNPs and the mitochondria membrane probe MitoTracker Red FM. BNPs were taken up by neuronal cell bodies, at dendrites, and at synapses, and the localization of BNPs was consistent with that of MitoTracker Red FM. The brain slices were stained with the BNPs, and the BNPs did not significantly affect the electrophysiological properties of neurons. Oxygen maps were generated in living brain slices where oxygen is found to be mostly consumed by mitochondria near synapses. Finally, the BNPs exhibited excellent response when the conditions varied from normoxic to hypoxic and when the neuronal activity was increased by increasing K+ concentration. This work demonstrates the capability of BNPs as a non-invasive tool in oxygen sensing and could provide fundamental insight into neuronal mechanisms and excitability research.

Clofilium-induced Block of Delayed Rectifier Type K+Current in Atrial Tumor Cells (AT-1 Cells)

1997 ◽  
Vol 29 (1) ◽  
pp. 301-307 ◽  
Author(s):  
Mohit Lal Bhattacharyya ◽  
Shukla Sarker ◽  
Kawonia P Mull ◽  
Qadriyyah Debnam
Keyword(s):  
Tumor Cells ◽  
Delayed Rectifier ◽  
Type K ◽  
K Current ◽  
Atrial Tumor

scholarly journals Two components of cardiac delayed rectifier K+ current. Differential sensitivity to block by class III antiarrhythmic agents.

1990 ◽  
Vol 96 (1) ◽  
pp. 195-215 ◽  
Author(s):  
M C Sanguinetti ◽  
N K Jurkiewicz
Keyword(s):  
Antiarrhythmic Agent ◽  
Reversal Potential ◽  
Differential Sensitivity ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Antiarrhythmic Agents ◽  
Class Iii ◽  
Activation Curve ◽  
Voltage Range ◽  
K Current

An envelope of tails test was used to show that the delayed rectifier K+ current (IK) of guinea pig ventricular myocytes results from the activation of two outward K+ currents. One current was specifically blocked by the benzenesulfonamide antiarrhythmic agent, E-4031 (IC50 = 397 nM). The drug-sensitive current, "IKr" exhibits prominent rectification and activates very rapidly relative to the slowly activating drug-insensitive current, "IKs." IKs was characterized by a delayed onset of activation that occurs over a voltage range typical of the classically described cardiac IK. Fully activated IKs, measured as tail current after 7.5-s test pulses, was 11.4 times larger than the fully activated IKr. IKr was also blocked by d-sotalol (100 microM), a less potent benzenesulfonamide Class III antiarrhythmic agent. The activation curve of IKr had a steep slope (+7.5 mV) and a negative half-point (-21.5 mV) relative to the activation curve of IKs (slope = +12.7 mV, half-point = +15.7 mV). The reversal potential (Erev) of IKr (-93 mV) was similar to EK (-94 mV for [K+]o = 4 mM), whereas Erev of IKs was -77 mV. The time constants for activation and deactivation of IKr made up a bell-shaped function of membrane potential, peaking between -30 and -40 mV (170 ms). The slope conductance of the linear portion of the fully activated IKr-V relation was 22.5 S/F. Inward rectification of this relation occurred at potentials greater than -50 mV, resulting in a voltage-dependent decrease in peak IKr at test potentials greater than 0 mV. Peak IKr at 0 mV averaged 0.8 pA/pF (n = 21). Although the magnitude of IKr was small relative to fully activated IKs, the two currents were of similar magnitude when measured during a relatively short pulse protocol (225 ms) at membrane potentials (-20 to +20 mV) typical of the plateau phase of cardiac action potentials.

Sign in / Sign up

Export Citation Format

Share Document