scholarly journals Dose-dependent and Isoform-specific Modulation of Ca2+ Channels by RGK GTPases

2006 ◽  
Vol 128 (5) ◽  
pp. 605-613 ◽  
Author(s):  
Lillian Seu ◽  
Geoffrey S. Pitt
Keyword(s):  
Current Amplitude ◽  
Dependent Manner ◽  
Β Subunit ◽  
Excitable Cells ◽  
Gating Kinetics ◽  
Channel Current ◽  
Mechanism Of Inhibition ◽  
High Affinity Binding Site ◽  
Dose Dependent ◽  
Ca2 Channels

Although inhibition of voltage-gated calcium channels by RGK GTPases (RGKs) represents an important mode of regulation to control Ca2+ influx in excitable cells, their exact mechanism of inhibition remains controversial. This has prevented an understanding of how RGK regulation can be significant in a physiological context. Here we show that RGKs—Gem, Rem, and Rem2—decreased CaV1.2 Ca2+ current amplitude in a dose-dependent manner. Moreover, Rem2, but not Rem or Gem, produced dose-dependent alterations on gating kinetics, uncovering a new mode by which certain RGKs can precisely modulate Ca2+ currents and affect Ca2+ influx during action potentials. To explore how RGKs influence gating kinetics, we separated the roles mediated by the Ca2+ channel accessory β subunit's interaction with its high affinity binding site in the pore-forming α1C subunit (AID) from its other putative contact sites by utilizing an α1C•β3 concatemer in which the AID was mutated to prevent β subunit interaction. This mutant concatemer generated currents with all the hallmarks of β subunit modulation, demonstrating that AID-β–independent interactions are sufficient for β subunit modulation. Using this construct we found that although inhibition of current amplitude was still partially sensitive to RGKs, Rem2 no longer altered gating kinetics, implicating different determinants for this specific mode of Rem2-mediated regulation. Together, these results offer new insights into the molecular mechanism of RGK-mediated Ca2+ channel current modulation.

scholarly journals Nesfatin-1 Suppresses Cardiac L-type Ca2+ Channels Through Melanocortin Type 4 Receptor and the Novel Protein Kinase C Theta Isoform Pathway

2015 ◽  
Vol 36 (2) ◽  
pp. 555-568 ◽  
Author(s):  
Jiaoqian Ying ◽  
Yuan Zhang ◽  
Shan Gong ◽  
Zhigang Chang ◽  
Xiaofeng Zhou ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Ventricular Myocytes ◽  
Dependent Manner ◽  
The Novel ◽  
Inotropic Effects ◽  
Kinase C ◽  
Melanocortin 4 Receptor ◽  
Dose Dependent ◽  
Ca2 Channels

Background/Aims: Nesfatin-1 (NF-1), an anorexic nucleobindin-2 (NUCB2)-derived hypothalamic peptide, acts as a peripheral cardiac modulator and it can induce negative inotropic effects. However, the mechanisms underlying these effects in cardiomyocytes remain unclear. Methods: Using patch clamp, protein kinase assays, and western blot analysis, we studied the effect of NF-1 on L-type Ca2+ currents (ICa,L) and to explore the regulatory mechanisms of this effect in adult ventricular myocytes. Results: NF-1 reversibly decreased ICa,L in a dose-dependent manner. This effect was mediated by melanocortin 4 receptor (MC4-R) and was associated with a hyperpolarizing shift in the voltage-dependence of inactivation. Dialysis of cells with GDP-β-S or anti-Gβ antibody as well as pertussis toxin pretreatment abolished the inhibitory effects of NF-1 on ICa,L. Protein kinase C (PKC) antagonists abolished NF-1-induced responses, whereas inhibition of PKA activity or intracellular application of the fast Ca2+-chelator BAPTA elicited no such effects. Application of NF-1 increased membrane abundance of PKC theta isoform (PKCθ), and PKCθ inhibition abolished the decrease in ICa,L induced by NF-1. Conclusion: These data suggest that NF-1 suppresses L-type Ca2+ channels via the MC4-R that couples sequentially to the βγ subunits of Gi/o-protein and the novel PKCθ isoform in adult ventricular myocytes.

GTP modulates run-up of whole-cell Ca2+ channel current in a Ca(2+)-dependent manner

1994 ◽  
Vol 71 (2) ◽  
pp. 814-816 ◽  
Author(s):  
J. J. Wagner ◽  
B. E. Alger
Keyword(s):  
Cell Voltage ◽  
Current Amplitude ◽  
Initial Increase ◽  
Absolute Maximum ◽  
Dependent Manner ◽  
Whole Cell ◽  
Ca1 Neurons ◽  
Channel Current ◽  
Run Up ◽  
Membrane Patch

1. Whole-cell voltage-clamp recordings were obtained from CA1 neurons acutely dissociated from rat hippocampus to study the effects of guanosine 5'-triphosphate (GTP) on the gradual increase in Ca2+ channel current amplitude that takes place over several minutes after breaking in to whole-cell mode ("run-up"). 2. Including GTP (500 microM) in the patch pipette significantly prolonged the duration of run-up of peak Ca2+ channel current to its maximum value compared with controls without GTP when the recording solutions contained Ca2+. On the other hand, GTP significantly enhanced run-up when Mg2+ and Ba2+ were substituted for intracellular and extracellular Ca2+, respectively. 3. The enhancement of run-up of the current in the Mg/Ba condition appeared to be due both to an initial increase in current amplitude that was complete within 30 s after break in and to a more rapid initial rate of run-up when compared with the Ca2+ condition. GTP did not affect the absolute maximum amplitudes of the currents in either Ca2+ or Ba2+ conditions. 4. We conclude that an early GTP-dependent modulation of Ca2+ channel current is qualitatively altered, depending on whether Ca2+ or Ba2+ is used as the charge carrier. Evidence of this modulation is apparent within seconds after rupture of the membrane patch. Conceivably, influences occurring during the period of "equilibration" with electrode contents could alter subsequent regulatory steps.

Effects of calcium channel blockers on spontaneous electrical activity of freshly isolated three-day-old embryonic chick ventricle

1996 ◽  
Vol 8 (5) ◽  
pp. 921 ◽  
Author(s):  
P Prakash ◽  
P Meera ◽  
O Tripathi
Keyword(s):  
Na Channel ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Embryonic Chick ◽  
Na Channels ◽  
Chronotropic Effect ◽  
High Doses ◽  
Dose Dependent ◽  
Ca2 Channels ◽  
Positive Chronotropic Effect

The effects of four major types of organic Ca2+ channel blockers, verapamil, nifedipine, diltiazem and fendiline and of tetrodotoxin (TXX), a fast Na+ channel blocker, on the action potential (AP) of freshly isolated 3-day-old embryonic chick ventricle (3d ECV) were investigated to resolve the controversy about the ionic basis of upstroke. The APs were characterized by a maximum diastolic potential (MDP) of -60 mV, an overshoot (Eov) of 16 mV and a maximum upstroke velocity (+Vmax) of 42 V s-1. All four Ca2+ channel blockers (0.1-40 microM) and TTX (0.1-80 nM) produced a dose-dependent reduction in +Vmax and Eov. MDP was also reduced by Ca2+ channel blockers in a dose-dependent manner but was unaffected by TTX. A significant linear correlation between MDP and +Vmax was observed for verapamil (r = 0.99), nifedipine (r = 0.99), diltiazem (r = 0.96) and fendiline (r = 0.98). Surprisingly, all Ca2+ channel blockers produced a dose-dependent positive chronotropic effect leading to cessation of firing at high doses (20-40 microM). In preparations becoming quiescent with high doses of verapamil (20-40 microM), elevated extracellular concentrations of Ca2+ (up to 9.6 nM) and isoproterenol (0.5-40 microM) failed to restore spontaneous APs. Electrical stimulation also failed to elicit APs in preparations inhibited by verapamil, diltiazem and fendiline. The inhibition of +Vmax by TTX demonstrates that fast Na+ channels were involved in the upstroke of AP in 3d ECV. Voltage-dependent inactivation of fast Na+ channels during depolarization (reduction in MDP) by the Ca2+ channel blockers explains their inhibitory effect on +Vmax and indicates that L-type Ca2+ channels had no significant role in the upstroke. A positive chronotropic effect of the Ca2+ channel blockers further suggests that slow Ca2+ channels are not involved in automaticity in freshly isolated 3d ECV.

scholarly journals Comparative Contractile Effects of Halothane and Sevoflurane in Rat Aorta

2000 ◽  
Vol 92 (1) ◽  
pp. 219-219 ◽  
Author(s):  
Vu Huu Vinh ◽  
Taijiro Enoki ◽  
Shinichi Hirata ◽  
Hiroshi Toda ◽  
Masahiro Kakuyama ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Thoracic Aorta ◽  
Volatile Anesthetic ◽  
Rat Aorta ◽  
Isometric Tension ◽  
Dependent Manner ◽  
Anesthetic Agents ◽  
Rat Thoracic Aorta ◽  
Dose Dependent ◽  
Ca2 Channels

Background Volatile anesthetic agents have been shown to have contractile effects in vascular tissues during specific conditions. This study compared contractile effects of halothane and sevoflurane in rat aorta treated with verapamil. This study also tried to elucidate the mechanism of the contraction. Methods Endothelium-denuded rat thoracic aorta was used for recording of isometric tension and measurement of influx of 45Ca2+. All experiments were performed in the presence of verapamil. In recording of tension, rings were precontracted with a submaximum dose of phenylephrine, followed by exposure to halothane or sevoflurane. For measurement of influx of 45Ca2+, rat aortic strips were exposed to phenylephrine and then to additional halothane or sevoflurane. Influx of Ca2+ was estimated by incubating the strips in 45Ca2+-labeled solution for 2 min. Results Halothane (0.5-4.0%) induced contraction in a dose-dependent manner, whereas sevoflurane (1-4%) had no effect on tension. Influx of 45Ca2+ was strongly enhanced by halothane at 1% and 2%, but only slightly at 4%, and was not affected by 1-4% sevoflurane. SK&F 96365, a blocker of voltage-independent Ca2+ channels, abolished contraction and influx of 45Ca2+ by 1% halothane. Depletion of Ca2+ from the sarcoplasmic reticulum with ryanodine or thapsigargin reduced the contraction induced by halothane at 4% but not that at 1% and 2%. Conclusion Halothane is suggested to cause contraction by enhancing influx of Ca2+ via voltage-independent Ca2+ channels at concentrations up to 2% and by inducing release of Ca2+ at 4%. Sevoflurane (1-4%) is devoid of these contractile effects.

scholarly journals Sitafloxacin Inhibits TNFα Release from Monocytic THP-1 Cells Stimulated by LPS

2021 ◽  
Author(s):  
Ippei Sakamaki ◽  
Michika Fukushi ◽  
Kazuhiro Itoh ◽  
Wakana Ohashi ◽  
Kei Tomihara ◽  
...  
Keyword(s):  
Septic Shock ◽  
Inflammatory Cytokines ◽  
Anaerobic Bacteria ◽  
Systemic Reaction ◽  
Dependent Manner ◽  
Antimicrobial Spectrum ◽  
Gram Negative ◽  
Cytokines And Chemokines ◽  
Mechanism Of Inhibition ◽  
Dose Dependent

Abstract Sepsis is a systemic reaction to infection and excessive production of inflammatory cytokines and chemokines. It sometimes results in septic shock. The present study was designated to find out which quinolone antibiotic reduces TNFα production the most and to elucidate its mechanisms. We examined which quinolone antibiotic reduced TNFα production from THP-1 cells stimulated by lipopolysaccharide (LPS). Then, we examined the mechanism of inhibition of TNFα production by the antibiotic. STFX most effectively reduced TNFα concentrations within LPS-stimulated THP-1 cells supernatant. STFX suppressed TNFα production in a dose-dependent manner. We found that STFX did not inhibit the NF-kB, ERK, or p38 pathways, nor did it inhibit the production of TNFα mRNA. The percentage of intracellular TNFα was increased in cells stimulated by LPS and with STFX compared to that of cells stimulated by LPS alone. In conclusion, one of the mechanisms reducing TNFα production from LPS-stimulated THP-1 cells treated with STFX involves inhibition of TNFα release from these cells. STFX has a broad antimicrobial spectrum for gram-positive, gram-negative, and anaerobic bacteria, and may be effective for treating sepsis by both killing bacteria and suppressing inflammation.

Alteration of ATP-sensitive K+ channels in rabbit aortic smooth muscle during left ventricular hypertrophy

2012 ◽  
Vol 303 (2) ◽  
pp. C170-C178 ◽  
Author(s):  
Won Sun Park ◽  
Da Hye Hong ◽  
Youn Kyoung Son ◽  
Min Hee Kim ◽  
Seung Hun Jeong ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Intracellular Signaling ◽  
Left Ventricular ◽  
Current Amplitude ◽  
Dependent Manner ◽  
Signaling Mechanism ◽  
Aortic Smooth Muscle ◽  
Channel Expression ◽  
The Right ◽  
Dose Dependent

We investigated the impairment of ATP-sensitive K+ (KATP) channels in aortic smooth muscle cells (ASMCs) from isoproterenol-induced hypertrophied rabbits. The amplitude of KATP channels induced by the KATP channel opener pinacidil (10 μM) was greater in ASMCs from control than from hypertrophied animals. In phenylephrine-preconstricted aortic rings, pinacidil induced relaxation in a dose-dependent manner. The dose-dependent curve was shifted to the right in the hypertrophied (EC50: 17.80 ± 3.28 μM) compared with the control model (EC50: 6.69 ± 2.40 μM). Although the level of Kir6.2 subtype expression did not differ between ASMCs from the control and hypertrophied models, those of the Kir6.1 and SUR2B subtypes were decreased in the hypertrophied model. Application of the calcitonin-gene related peptide (100 nM) and adenylyl cyclase activator forskolin (10 μM), which activates protein kinase A (PKA) and consequently KATP channels, induced a KATP current in both control and hypertrophied animals; however, the KATP current amplitude did not differ between the two groups. Furthermore, PKA expression was not altered between the control and hypertrophied animals. These results suggests that the decreased KATP current amplitude and KATP channel-induced vasorelaxation in the hypertrophied animals were attributable to the reduction in KATP channel expression but not to changes in the intracellular signaling mechanism that activates the KATP current.

Meclofenamate inhibits prostaglandin E binding and adenylyl cyclase activation in human myometrium

1991 ◽  
Vol 129 (3) ◽  
pp. 439-445 ◽  
Author(s):  
A. López Bernal ◽  
S. Buckley ◽  
C. M. P. Rees ◽  
J. M. Marshall
Keyword(s):  
Inhibitory Effect ◽  
Human Myometrium ◽  
Prostaglandin E ◽  
Dependent Manner ◽  
Synthesis Inhibitor ◽  
Traditional Role ◽  
Mechanism Of Inhibition ◽  
Receptor Sites ◽  
Competitive Mechanism ◽  
Dose Dependent

ABSTRACT The effect of sodium meclofenamate on the binding of [3H]prostaglandin E2 ([3H]PGE2) to membranes from human myometrium was investigated. Meclofenamate inhibited the binding of [3H]PGE2 to high-affinity (dissociation constant 1·5 nmol/l) sites in a reversible dose-dependent manner (inhibition constant 11 μmol/l). The mechanism of inhibition was mainly competitive, but at high doses of meclofenamate (≥ 100 μmol/l) there was loss of PGE receptor sites. Of several PG synthesis inhibitors tested, only meclofenamate and, to a lesser extent, mefenamic acid had a significant inhibitory effect. PGE2 stimulated cyclic AMP generation in slices of human myometrium and this was inhibited by meclofenamate in a dose-dependent manner (50% inhibition occurred at 9 μmol/l). Again, this effect was specific for meclofenamate and fitted a competitive mechanism at doses in the range 1–10 μmol/l and a non-competitive mechanism at higher doses. The data show that meclofenamate, in addition to its traditional role as a PG synthesis inhibitor, affects directly PGE receptor binding and activation. Journal of Endocrinology (1991) 129, 439–445

scholarly journals Immunosuppressive effect of the Fusarium secondary metabolite butenolide in human colon epithelial cells

2020 ◽  
Author(s):  
Lydia Woelflingseder ◽  
Gerhard Adam ◽  
Doris Marko
Keyword(s):  
Inflammatory Response ◽  
Secondary Metabolite ◽  
Human Colon ◽  
Dependent Manner ◽  
Fungal Metabolites ◽  
Food Contaminants ◽  
Trichothecene Mycotoxin ◽  
Mechanism Of Inhibition ◽  
Tnf Α ◽  
Dose Dependent

ABSTRACTButenolide (BUT, 4-acetamido-4-hydroxy-2-butenoic acid gamma-lactone) is a secondary metabolite produced by several Fusarium species and is co-produced with the major trichothecene mycotoxin deoxynivalenol (DON) on cereal grains throughout the world. BUT has low acute toxicity and only very limited occurrence and exposure data are available. The intestinal epithelium represents the first physiological barrier against food contaminants. We aimed to elucidate the intestinal inflammatory response of the human, non-cancer epithelial HCEC-1CT cells to BUT and to characterize potential combinatory interactions with co-occurring trichothecenes, such as DON and NX-3. Using a reporter gene approach, BUT (≥5 μM, 20 h) was found to decrease lipopolysaccharide (LPS; 10 ng/mL) induced nuclear factor kappa B (NF-κB) activation in a dose-dependent manner, and in combinatory treatments represses trichothecene-induced enhancement of this important inflammatory pathway. Analyzing transcription and secretion levels of NF-κB-dependent, pro-inflammatory cytokines, revealed a significant down-regulation of IL-1β, IL-6 and TNF-α in IL-1β-stimulated (25 ng/mL) HCEC-1CT cells after BUT exposure (10 μM). Trichothecene-induced expression of pro-in-flammatory cytokines by the presence of 1 μM DON or NX-3 was substantially suppressed in the presence of 10 μM BUT. The emerging mycotoxin BUT has the ability to suppress NF-κB-induced intestinal inflammatory response mechanisms and to modulate substantially the immune responsiveness of HCEC-1CT cells after trichothecene treatment. Our results suggest that BUT, present in naturally occurring mixtures of Fusarium fungal metabolites, should be increasingly monitored, and the mechanism of inhibition of NF-κB that might affect the pathogenesis or progression of intestinal inflammatory disorders, should be further investigated.

Modulation of cardiac Ca2+channels by isoproterenol studied in transgenic mice with altered SR Ca2+ content

1997 ◽  
Vol 273 (5) ◽  
pp. C1666-C1672 ◽  
Author(s):  
Hidenori Sako ◽  
Stuart A. Green ◽  
Evangelia G. Kranias ◽  
Atsuko Yatani
Keyword(s):  
Adrenergic Receptor ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Dependent Manner ◽  
Wild Type ◽  
Decay Kinetics ◽  
Cardiac Contractile ◽  
Subsequent Application ◽  
Dose Dependent ◽  
Ca2 Channels

Phospholamban (PLB) ablation is associated with enhanced sarcoplasmic reticulum (SR) Ca2+ uptake and attenuation of the cardiac contractile responses to β-adrenergic agonists. In the present study, we compared the effects of isoproterenol (Iso) on the Ca2+ currents ( I Ca) of ventricular myocytes isolated from wild-type (WT) and PLB knockout (PLB-KO) mice. Current density and voltage dependence of I Ca were similar between WT and PLB-KO cells. However, I Ca recorded from PLB-KO myocytes had significantly faster decay kinetics. Iso increased I Ca amplitude in both groups in a dose-dependent manner (50% effective concentration, 57.1 nM). Iso did not alter the rate of I Ca inactivation in WT cells but significantly prolonged the rate of inactivation in PLB-KO cells. When Ba2+ was used as the charge carrier, Iso slowed the decay of the current in both WT and PLB-KO cells. Depletion of SR Ca2+ by ryanodine also slowed the rate of inactivation of I Ca, and subsequent application of Iso further reduced the inactivation rate of both groups. These results suggest that enhanced Ca2+ release from the SR offsets the slowing effects of β-adrenergic receptor stimulation on the rate of inactivation of I Ca.

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