scholarly journals Influence of Serotonin 5-HT4 Receptors on Responses to Cardiac Stressors in Transgenic Mouse Models

Biomedicines ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 569
Author(s):  
Ulrich Gergs ◽  
Timo Gerigk ◽  
Jonas Wittschier ◽  
Constanze T. Schmidbaur ◽  
Clara Röttger ◽  
...  
Keyword(s):  
Cardiac Myocytes ◽  
Left Atrial ◽  
Cardiac Contractility ◽  
Mechanical Function ◽  
Transgenic Mouse Models ◽  
Wild Type ◽  
Novel Drug ◽  
Perfused Hearts ◽  
Underlying Pathology

The current study aimed to deepen our knowledge on the role of cardiac 5-HT4 receptors under pathophysiological conditions. To this end, we used transgenic (TG) mice that overexpressed human 5-HT4a receptors solely in cardiac myocytes (5-HT4-TG mice) and their wild-type (WT) littermates that do not have functional cardiac 5-HT4 receptors as controls. We found that an inflammation induced by lipopolysaccharide (LPS) was detrimental to cardiac function in both 5-HT4-TG and WT mice. In a hypoxia model, isolated left atrial preparations from the 5-HT4-TG mice went into contracture faster during hypoxia and recovered slower following hypoxia than the WT mice. Similarly, using isolated perfused hearts, 5-HT4-TG mice hearts were more susceptible to ischemia compared to WT hearts. To study the influence of 5-HT4 receptors on cardiac hypertrophy, 5-HT4-TG mice were crossbred with TG mice overexpressing the catalytic subunit of PP2A in cardiac myocytes (PP2A-TG mice, a model for genetically induced hypertrophy). The cardiac contractility, determined by echocardiography, of the resulting double transgenic mice was attenuated like in the mono-transgenic PP2A-TG and, therefore, largely determined by the overexpression of PP2A. In summary, depending on the kind of stress put upon the animal or isolated tissue, 5-HT4 receptor overexpression could be either neutral (genetically induced hypertrophy, sepsis) or possibly detrimental (hypoxia, ischemia) for mechanical function. We suggest that depending on the underlying pathology, the activation or blockade of 5-HT4 receptors might offer novel drug therapy options in patients.

Differential effects of phospholamban and Ca2+/calmodulin-dependent kinase II on [Ca2+]i transients in cardiac myocytes at physiological stimulation frequencies

2008 ◽  
Vol 294 (5) ◽  
pp. H2352-H2362 ◽  
Author(s):  
Andreas A. Werdich ◽  
Eduardo A. Lima ◽  
Igor Dzhura ◽  
Madhu V. Singh ◽  
Jingdong Li ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Wild Type ◽  
Dependent Protein Kinase ◽  
Frequency Dependent ◽  
Physiological Range ◽  
Dependent Protein ◽  
Isolated Cardiac Myocytes

In cardiac myocytes, the activity of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) is hypothesized to regulate Ca2+ release from and Ca2+ uptake into the sarcoplasmic reticulum via the phosphorylation of the ryanodine receptor 2 and phospholamban (PLN), respectively. We tested the role of CaMKII and PLN on the frequency adaptation of cytosolic Ca2+ concentration ([Ca2+]i) transients in nearly 500 isolated cardiac myocytes from transgenic mice chronically expressing a specific CaMKII inhibitor, interbred into wild-type or PLN null backgrounds under physiologically relevant pacing conditions (frequencies from 0.2 to 10 Hz and at 37°C). When compared with that of mice lacking PLN only, the combined chronic CaMKII inhibition and PLN ablation decreased the maximum Ca2+ release rate by more than 50% at 10 Hz. Although PLN ablation increased the rate of Ca2+ uptake at all frequencies, its combination with CaMKII inhibition did not prevent a frequency-dependent reduction of the amplitude and the duration of the [Ca2+]i transient. High stimulation frequencies in the physiological range diminished the effects of PLN ablation on the decay time constant and on the maximum decay rate of the [Ca2+]i transient, indicating that the PLN-mediated feedback on [Ca2+]i removal is limited by high stimulation frequencies. Taken together, our results suggest that in isolated mouse ventricular cardiac myocytes, the combined chronic CaMKII inhibition and PLN ablation slowed Ca2+ release at physiological frequencies: the frequency-dependent decay of the amplitude and shortening of the [Ca2+]i transient occurs independent of chronic CaMKII inhibition and PLN ablation, and the PLN-mediated regulation of Ca2+ uptake is diminished at higher stimulation frequencies within the physiological range.

scholarly journals Cerebrovascular Changes and Neurodegeneration Related to Hyperlipidemia: Characteristics of the Human ApoB-100 Transgenic Mice

2020 ◽  
Vol 26 (13) ◽  
pp. 1486-1494 ◽  
Author(s):  
Melinda E. Tóth ◽  
Brigitta Dukay ◽  
Zsófia Hoyk ◽  
Miklós Sántha
Keyword(s):  
Transgenic Mouse ◽  
Serum Lipid ◽  
Lipoprotein Metabolism ◽  
Transgenic Mouse Models ◽  
Wild Type ◽  
Lipid Levels ◽  
Cerebrovascular Lesions ◽  
Wide Range ◽  
And Function

Serum lipid levels are closely related to the structure and function of blood vessels. Chronic hyperlipidemia may lead to damage in both the cardio- and the cerebrovascular systems. Vascular dysfunctions, including impairments of the blood-brain barrier, are known to be associated with neurodegenerative diseases. A growing number of evidence suggests that cardiovascular risk factors, such as hyperlipidemia, may increase the likelihood of developing dementia. Due to differences in lipoprotein metabolism, wild-type mice are protected against dietinduced hypercholesterolemia, and their serum lipid profile is different from that observed in humans. Therefore, several transgenic mouse models have been established to study the role of different apolipoproteins and their receptors in lipid metabolism, as well as the complications related to pathological lipoprotein levels. This minireview focused on a transgenic mouse model overexpressing an apolipoprotein, the human ApoB-100. We discussed literature data and current advancements on the understanding of ApoB-100 induced cardio- and cerebrovascular lesions in order to demonstrate the involvement of this type of apolipoprotein in a wide range of pathologies, and a link between hyperlipidemia and neurodegeneration.

Abstract 2375: Regulation of Cardiac Myocyte Contractility by Phospholemman

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Jianliang Song ◽  
Xue-Qian Zhang ◽  
JuFang Wang ◽  
Ellina Cheskis ◽  
Tung O Chan ◽  
...  
Keyword(s):  
Cardiac Myocytes ◽  
Cardiac Myocyte ◽  
Adult Mouse ◽  
Surface Membrane ◽  
Cardiac Contractility ◽  
Wild Type ◽  
Inhibitory Effects ◽  
Normal Surface ◽  
Membrane Area ◽  
Myocyte Contractility

Phospholemman (PLM) regulates cardiac contractility by modulating Na + /Ca 2+ exchanger (NCX1) and/or Na + -K + -ATPase activities. PLM, when phosphorylated at serine68, disinhibits Na + -K + -ATPase but inhibits NCX1. In this study, we first demonstrated that adult mouse cardiac myocytes cultured for 48 hours had normal surface membrane area and t-tubule appearance, and exhibited near normal contractility. Contractile differences between wild-type (WT) and PLM knockout (KO) myocytes were preserved after 48h of culture. Infection with adenovirus overexpressing GFP did not affect contractility at 48h. When WT PLM was overexpressed in PLM-KO myocytes, part of PLM was phosphorylated, both Na + -K + -ATPase current (I pump ) and Na + /Ca 2+ exchange current (I NaCa ) were depressed, and contractility and [Ca 2+ ] i transients reverted back to those observed in cultured WT myocytes. Overexpressing PLMS68E mutant (phosphomimetic) in PLM-KO myocytes resulted in suppression of I NaCa but no effect on I pump . Contractility and [Ca 2+ ] i transient amplitudes in PLM-KO myocytes overexpressing PLMS68E mutant were depressed when compared to PLM-KO myocytes overexpressing GFP. Overexpressing PLMS68A mutant (mimicking unphosphorylated PLM) in PLM-KO myocytes had no effects on I NaCa but decreased I pump . Contractility and [Ca 2+ ] i transient amplitudes in PLM-KO myocytes overexpressing S68A mutant were similar to PLM-KO myocytes overexpressing GFP. Neither WT PLM nor its mutants had any effect on SR Ca 2+ uptake in KO myocytes. We conclude that at the single myocyte level, PLM affects cardiac contractility and [Ca 2+ ] i homeostasis primarily by its direct inhibitory effects on Na + /Ca 2+ exchange.

New insights into the molecular and cellular workings of the cardiac Na+/Ca2+ exchanger

2004 ◽  
Vol 287 (5) ◽  
pp. C1167-C1172 ◽  
Author(s):  
Donald W. Hilgemann
Keyword(s):  
Cardiac Myocytes ◽  
Driving Force ◽  
Regulatory Domain ◽  
Wild Type ◽  
Regulatory Domains ◽  
Pump Activity ◽  
Extrusion Mechanism ◽  
Rat Myocytes ◽  
Contraction Cycle

The cardiac Na+/Ca2+ exchanger (NCX1) is almost certainly the major Ca2+ extrusion mechanism in cardiac myocytes, although the driving force for Ca2+ extrusion is quite small. To explain multiple recent results, it is useful to think of the exchanger as a slow Ca2+ buffer that can reverse its function multiple times during the excitation-contraction cycle (ECC). An article by the group of John Reeves brings new insights to this function by analyzing the role of regulatory domains of NCX1 that mediate its activation by a rise of cytoplasmic Ca2+. It was demonstrated that the gating reactions are operative just in the physiological range of Ca2+ changes, a few fold above resting Ca2+ level, and that they prevent the exchanger from damping out the influence of mechanisms that transiently increase Ca2+ levels. Furthermore, exchangers with deleted regulatory domains are shown to reduce resting Ca2+ to lower levels than achieved by wild-type exchangers. A study by the group of Kenneth Philipson demonstrated that the NCX1 regulatory domain can bind and respond to Ca2+ changes on the time scale of the ECC in rat myocytes. At the same time, studies of transgenic mice and NCX1 knockout mice generated by the Philipson group revealed that large changes of NCX1 activity have rather modest effects on ECC. Simple simulations predict these results very well: murine cardiac ECC is very sensitive to small changes of the Na+ gradient, very sensitive to changes of the sarcoplasmic reticulum Ca2+ pump activity, and very insensitive to changes of NCX1 activity. It is speculated that the NCX1 gating reactions not only regulate coupled 3Na+:1Ca2+ exchange but also control the exchanger’s Na+ leak function that generates background Na+ influx and depolarizing current in cardiac myocytes.

scholarly journals Cardiac Gsα overexpression enhances L-type calcium channels through an adenylyl cyclase independent pathway

1998 ◽  
Vol 95 (16) ◽  
pp. 9669-9674 ◽  
Author(s):  
Alan S. Lader ◽  
Yong-Fu Xiao ◽  
Yoshihiro Ishikawa ◽  
Yanning Cui ◽  
Dorothy E. Vatner ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Transgenic Mice ◽  
Protein Kinase A ◽  
Adenylyl Cyclase ◽  
Cardiac Myocytes ◽  
Receptor Activation ◽  
Wild Type ◽  
Α Subunit ◽  
Kinase A

The α subunit of the stimulatory heterotrimeric G protein (Gsα) is critical for the β-adrenergic receptor activation of the cAMP messenger system. The role of Gsα in regulating cardiac Ca2+ channel activity, however, remains controversial. Cultured neonatal cardiac myocytes from transgenic mice overexpressing cardiac Gsα were used to assess the role of Gsα on the whole-cell Ca2+ currents (ICa). Cardiac myocytes from transgenic mice had a 490% higher peak ICa compared with those of either wild-type controls or Gsα-nonexpressing littermates. The effect of Gsα overexpression was mimicked by intracellular dialysis of wild-type cardiac myocytes with GTPγS-activated Gsα. This effect was not mediated by protein kinase A activation as intracellular perfusion with a protein kinase A inhibitor rendered the same degree of activation in either transgenic or wild-type myocytes also dialyzed with activated Gsα. The data indicate that Gsα overexpression is associated with a constitutive enhancement of ICa which is independent of the cAMP pathway and activation of endogenous adenylyl cyclase.

scholarly journals Allosteric Regulation of Na/Ca Exchange Current by Cytosolic Ca in Intact Cardiac Myocytes

2001 ◽  
Vol 117 (2) ◽  
pp. 119-132 ◽  
Author(s):  
Christopher R. Weber ◽  
Kenneth S. Ginsburg ◽  
Kenneth D. Philipson ◽  
Thomas R. Shannon ◽  
Donald M. Bers
Keyword(s):  
Cardiac Myocytes ◽  
Allosteric Regulation ◽  
Wild Type Mouse ◽  
Wild Type ◽  
Physiological Conditions ◽  
Model Predictions ◽  
Electrochemical Effect ◽  
Fine Tune

The cardiac sarcolemmal Na-Ca exchanger (NCX) is allosterically regulated by [Ca]i such that when [Ca]i is low, NCX current (INCX) deactivates. In this study, we used membrane potential (Em) and INCX to control Ca entry into and Ca efflux from intact cardiac myocytes to investigate whether this allosteric regulation (Ca activation) occurs with [Ca]i in the physiological range. In the absence of Ca activation, the electrochemical effect of increasing [Ca]i would be to increase inward INCX (Ca efflux) and to decrease outward INCX. On the other hand, Ca activation would increase INCX in both directions. Thus, we attributed [Ca]i-dependent increases in outward INCX to allosteric regulation. Ca activation of INCX was observed in ferret myocytes but not in wild-type mouse myocytes, suggesting that Ca regulation of NCX may be species dependent. We also studied transgenic mouse myocytes overexpressing either normal canine NCX or this same canine NCX lacking Ca regulation (Δ680–685). Animals with the normal canine NCX transgene showed Ca activation, whereas animals with the mutant transgene did not, confirming the role of this region in the process. In native ferret cells and in mice with expressed canine NCX, allosteric regulation by Ca occurs under physiological conditions (KmCaAct = 125 ± 16 nM SEM ≈ resting [Ca]i). This, along with the observation that no delay was observed between measured [Ca]i and activation of INCX under our conditions, suggests that beat to beat changes in NCX function can occur in vivo. These changes in the INCX activation state may influence SR Ca load and resting [Ca]i, helping to fine tune Ca influx and efflux from cells under both normal and pathophysiological conditions. Our failure to observe Ca activation in mouse myocytes may be due to either the extent of Ca regulation or to a difference in KmCaAct from other species. Model predictions for Ca activation, on which our estimates of KmCaAct are based, confirm that Ca activation strongly influences outward INCX, explaining why it increases rather than declines with increasing [Ca]i.

scholarly journals Role of phospholemman phosphorylation sites in mediating kinase-dependent regulation of the Na+-K+-ATPase

2010 ◽  
Vol 299 (6) ◽  
pp. C1363-C1369 ◽  
Author(s):  
Fei Han ◽  
Julie Bossuyt ◽  
Jody L. Martin ◽  
Sanda Despa ◽  
Donald M. Bers
Keyword(s):  
Cardiac Myocytes ◽  
Double Mutant ◽  
Phosphorylation Sites ◽  
Wild Type ◽  
Pump Rate ◽  
Necessary And Sufficient ◽  
Pkc Activation ◽  
Major Target ◽  
In Cells

Phospholemman (PLM) is a major target for phosphorylation mediated by both PKA (at Ser68) and PKC (at both Ser63 and Ser68) in the heart. In intact cardiac myocytes, PLM associates with and inhibits Na+-K+-ATPase (NKA), mainly by reducing its affinity for internal Na+. The inhibition is relieved upon PLM phosphorylation by PKA or PKC. The aim here was to distinguish the role of the Ser63 and Ser68 PLM phosphorylation sites in mediating kinase-induced modulation of NKA function. We expressed wild-type (WT) PLM and S63A, S68A, and AA (Ser63 and Ser68 to alanine double mutant) PLM mutants in HeLa cells that stably express rat NKA-α1 and we measured the effect of PKA and PKC activation on NKA-mediated intracellular Na+ concentration decline. PLM expression (WT or mutant) significantly decreased the apparent NKA affinity for internal Na+ and had no significant effect on the maximum pump rate ( Vmax). PKA activation with forskolin (20 μM) restored NKA Na+ affinity in cells expressing WT but not AA PLM and did not affect Vmax in either case. Similarly, PKC activation with 300 nM phorbol 12,13-dibutyrate increased NKA Na+ affinity in cells expressing WT, S63A, and S68A PLM and had no effect in cells expressing AA PLM. Neither forskolin nor phorbol 12,13-dibutyrate affected NKA function in the absence of PLM. We conclude that PLM phosphorylation at either Ser63 or Ser68 is both necessary and sufficient for completely relieving the PLM-induced NKA inhibition.

scholarly journals Kir6.2 is not the mitochondrial KATP channel but is required for cardioprotection by ischemic preconditioning

2013 ◽  
Vol 304 (11) ◽  
pp. H1439-H1445 ◽  
Author(s):  
Andrew P. Wojtovich ◽  
William R. Urciuoli ◽  
Shampa Chatterjee ◽  
Aron B. Fisher ◽  
Keith Nehrke ◽  
...  
Keyword(s):  
Ischemic Preconditioning ◽  
Ischemia Reperfusion ◽  
Cardiac Response ◽  
Cardiac Mitochondria ◽  
Channel Activity ◽  
Wild Type ◽  
Mitochondrial Katp Channel ◽  
Baseline Response ◽  
Perfused Hearts

ATP-sensitive K+ (KATP) channels that contain K+ inward rectifier subunits of the 6.2 isotype (Kir6.2) are important regulators of the cardiac response to ischemia-reperfusion (I/R) injury. Opening of these channels is implicated in the cardioprotective mechanism of ischemic preconditioning (IPC), but debate surrounds the contribution of surface KATP (sKATP) versus mitochondrial KATP (mKATP) channels. While responses to I/R injury and IPC have been examined in Kir6.2−/− mice before, breeding methods and other technical obstacles may have confounded interpretations. The aim of this study was to elucidate the role of Kir6.2 in cardioprotection and mKATP activity, using conventionally bred Kir6.2−/− mice with wild-type littermates as controls. We found that perfused hearts from Kir6.2−/− mice exhibited a normal baseline response to I/R injury, were not protected by IPC, and showed a blunted response to the IPC mimetic drug diazoxide. These data suggest that the loss of IPC in Kir6.2−/− hearts is not due to an underlying difference in I/R sensitivity. Furthermore, mKATP channel activity was identical in cardiac mitochondria isolated from wild-type versus Kir6.2−/− mice, suggesting no role for Kir6.2 in the mKATP. Collectively, these data indicate that Kir6.2 is required for the full response to IPC or diazoxide but is not involved in mKATP formation.

scholarly journals The EMT transcription factor Snai1 maintains myocardial wall integrity by repressing intermediate filament gene expression

2020 ◽  
Author(s):  
Alessandra Gentile ◽  
Anabela Y.R. Bensimon-Brito ◽  
Rashmi Priya ◽  
Hans-Martin Maischein ◽  
Janett Piesker ◽  
...  
Keyword(s):  
Gene Expression ◽  
Transcription Factor ◽  
Intermediate Filament ◽  
Epithelial To Mesenchymal Transition ◽  
Cardiac Development ◽  
Cardiac Contractility ◽  
Wild Type ◽  
Mesenchymal Transition ◽  
Myocardial Wall

The zinc finger transcription factor Snai1 is a well-known regulator of epithelial-to-mesenchymal transition (EMT)1, 2; it is required for mesoderm ingression in flies3 and neural crest delamination in vertebrates4. During cardiac development, Snai1-regulated EMT is necessary for myocardial precursor migration and valve formation5, 6. However, a role for Snai1 in maturing cardiomyocytes (CMs) has not been reported. Here, using genetic, transcriptomic and chimeric analyses in zebrafish, we find that Snai1b is required for myocardial wall integrity. Global loss of snai1b leads to the extrusion of CMs away from the cardiac lumen, a process we show is dependent on cardiac contractility. Examining CM junctions in snai1b mutants, we observed that N-cadherin localization was compromised, thereby likely weakening cell-cell adhesion. In addition, extruding CMs exhibit increased actomyosin contractility basally, as revealed by the specific enrichment of canonical markers of actomyosin tension - phosphorylated myosin light chain (active myosin) and the α-catenin epitope α-18. By comparing the transcriptome of wild-type and snai1b mutant hearts at early stages of CM extrusion, we found the dysregulation of intermediate filament genes in mutants including the upregulation of desmin b. We tested the role of desmin b in myocardial wall integrity and found that CM-specific desmin b overexpression led to CM extrusion, recapitulating the snai1b mutant phenotype. Altogether, these results indicate that Snai1 is a critical regulator of intermediate filament gene expression in CMs, and that it maintains the integrity of the myocardial epithelium during embryogenesis, at least in part by repressing desmin b expression.

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