scholarly journals Induced cardiac pacemaker cells survive metabolic stress owing to their low metabolic demand

2019 ◽  
Vol 51 (9) ◽  
pp. 1-12 ◽  
Author(s):  
Jin-mo Gu ◽  
Sandra I. Grijalva ◽  
Natasha Fernandez ◽  
Elizabeth Kim ◽  
D. Brian Foster ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Cardiac Pacemaker ◽  
Metabolic Stress ◽  
Mitochondrial Morphology ◽  
Electrical Excitation ◽  
Metabolic Demand ◽  
Pacemaker Cells ◽  
Membrane Fusion Protein ◽  
Mitochondrial Inner Membrane ◽  
Metabolic Stresses

Abstract Cardiac pacemaker cells of the sinoatrial node initiate each and every heartbeat. Compared with our understanding of the constituents of their electrical excitation, little is known about the metabolic underpinnings that drive the automaticity of pacemaker myocytes. This lack is largely owing to the scarcity of native cardiac pacemaker myocytes. Here, we take advantage of induced pacemaker myocytes generated by TBX18-mediated reprogramming (TBX18-iPMs) to investigate comparative differences in the metabolic program between pacemaker myocytes and working cardiomyocytes. TBX18-iPMs were more resistant to metabolic stresses, exhibiting higher cell viability upon oxidative stress. TBX18-induced pacemaker myocytes (iPMs) expensed a lower degree of oxidative phosphorylation and displayed a smaller capacity for glycolysis compared with control ventricular myocytes. Furthermore, the mitochondria were smaller in TBX18-iPMs than in the control. We reasoned that a shift in the balance between mitochondrial fusion and fission was responsible for the smaller mitochondria observed in TBX18-iPMs. We identified a mitochondrial inner membrane fusion protein, Opa1, as one of the key mediators of this process and demonstrated that the suppression of Opa1 expression increases the rate of synchronous automaticity in TBX18-iPMs. Taken together, our data demonstrate that TBX18-iPMs exhibit a low metabolic demand that matches their mitochondrial morphology and ability to withstand metabolic insult.

scholarly journals Small functional If current in sinoatrial pacemaker cells of the brown trout (Salmo trutta fario) heart despite strong expression of HCN channel transcripts

2017 ◽  
Vol 313 (6) ◽  
pp. R711-R722 ◽  
Author(s):  
Minna Hassinen ◽  
Jaakko Haverinen ◽  
Matti Vornanen
Keyword(s):  
Brown Trout ◽  
Salmo Trutta ◽  
Ventricular Myocytes ◽  
Expression System ◽  
Cardiac Pacemaker ◽  
Transcript Abundance ◽  
Hcn Channels ◽  
Pacemaker Cells ◽  
Brown Trout Salmo Trutta ◽  
Salmo Trutta Fario

Funny current ( If), formed by hyperpolarization-activated cyclic nucleotide-gated channels (HCN channels), is supposed to be crucial for the membrane clock regulating the cardiac pacemaker mechanism. We examined the presence and activity of HCN channels in the brown trout ( Salmo trutta fario) sinoatrial (SA) pacemaker cells and their putative role in heart rate ( fH) regulation. Six HCN transcripts (HCN1, HCN2a, HCN2ba, HCN2bb, HCN3, and HCN4) were expressed in the brown trout heart. The total HCN transcript abundance was 4.0 and 4.9 times higher in SA pacemaker tissue than in atrium and ventricle, respectively. In the SA pacemaker, HCN3 and HCN4 were the main isoforms representing 35.8 ± 2.7 and 25.0 ± 1.5%, respectively, of the total HCN transcripts. Only a small If with a mean current density of −1.2 ± 0.37 pA/pF at −140 mV was found in 4 pacemaker cells out of 16 spontaneously beating cells examined, despite the optimization of recording conditions for If activity. If was not found in any of the 24 atrial myocytes and 21 ventricular myocytes examined. HCN4 coexpressed with the MinK-related peptide 1 (MiRP1) β-subunit in CHO cells generated large If currents. In contrast, HCN3 (+MiRP1) failed to produce If in the same expression system. Cs+ (2 mM), which blocked 84 ± 12% of the native If, reversibly reduced fH 19.2 ± 3.6% of the excised multicellular pacemaker tissue from 53 ± 5 to 44 ± 5 beats/min ( P < 0.05). However, this effect was probably due to the reduction of IKr, which was also inhibited (63.5 ± 4.6%) by Cs+. These results strongly suggest that fH regulation in the brown trout heart is largely independent on If.

Normal spontaneous firing of cardiac pacemaker cells is regulated by basal pkc delta activation

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
T Vinogradova ◽  
K Tarasov ◽  
D Riordon ◽  
Y Tarasova ◽  
E Lakatta
Keyword(s):  
Protein Kinase ◽  
Cycle Length ◽  
Cardiac Pacemaker ◽  
Funding Source ◽  
Spontaneous Firing ◽  
Pacemaker Cells ◽  
Patch Clamp Technique ◽  
Sa Node ◽  
Pkc Delta ◽  
Pkc Isoforms

Abstract   The spontaneous beating rate of rabbit sinoatrial node cells (SANC) is regulated by local subsarcolemmal calcium releases (LCRs) from sarcoplasmic reticulum (SR). LCRs appear during diastolic depolarization (DD) and activate an inward sodium/calcium exchange current which increases DD rate and thus accelerates spontaneous SANC firing. High basal level of protein kinase A and calcium/calmodulin-dependent protein kinase II phosphorylation are required to sustain basal LCRs and normal spontaneous SANC firing. Recently we discovered that basal PKC activation is also obligatory for cardiac pacemaker function: inhibition of PKC activity by broad spectrum PKC inhibitors Bis I or calphostin C markedly suppressed SR calcium cycling and decreased or abolished spontaneous beating of freshly isolated rabbit SANC. Here we studied which PKC isoforms mediate PKC-dependent effects on cardiac pacemaker cell automaticity. The PKC superfamily consists of 3 major subgroups: conventional, novel and atypical. All PKC isoforms were detected at the RNA level (RT-qPCR) in the rabbit SA node and ventricle, and expression levels were comparable in both tissues. Expression of PKCβ, however, was markedly higher in the rabbit SA node, compared to other PKC isoenzymes in either tissue. We verified expression of conventional PKC (α, β) and novel PKC-delta at the protein level in SANC and ventricular myocytes (VM). Western blot confirmed RNA results, showing a 6-fold higher PKCβ protein abundance in SANC compared to VM. Expression of PKCα protein was similar in both cell types, while PKC-delta protein was more abundant in VM. To study whether PKCβ regulates spontaneous beating of SANC we employed selective inhibitor of conventional (α, β, gamma) PKC isoforms Go6976 (10 μmol/L), which had no effects on either LCR characteristics (confocal microscopy, calcium indicator Fluo-3AM) or spontaneous beating of freshly isolated rabbit SANC (perforated patch-clamp technique). Because selective PKC-delta inhibitors are not available, we explored effects of PKC-delta inhibition comparing effects of Go6976 (the inhibitor of conventional PKCs) and Go6983, which inhibits conventional PKCs and PKC-delta. In contrast to Go6976, Go6983 (5 μmol/L) markedly decreased the LCR size (from 7.1±0.4 to 4.5±0.3 μm) and number per each spontaneous cycle (from 1.3±0.1 to 0.8±0.1). It also markedly increased the LCR period (time from the prior AP-induced calcium transient to the subsequent LCR) which was paralleled by an increase in the spontaneous SANC cycle length. Rottlerin, another PKC-delta inhibitor, produced similar effects on LCR characteristics, and markedly and time-dependently decreased DD rate, leading to an increase in the spontaneous cycle length, and finally abrogated the spontaneous SANC firing. Thus, our data indicate that basal activity of PKC-delta, but not that of PKCβ, is essential for generation of LCRs and normal spontaneous firing of cardiac pacemaker cells. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Intramural Research Program, National Institute on Aging, National Institute of Health, USA

Characterization of a TTX-sensitive Na+ current in pacemaker cells isolated from rabbit sinoatrial node

1996 ◽  
Vol 270 (6) ◽  
pp. H2108-H2119 ◽  
Author(s):  
H. Muramatsu ◽  
A. R. Zou ◽  
G. A. Berkowitz ◽  
R. D. Nathan
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Pacemaker Cells ◽  
Na Current ◽  
Recovery From Inactivation ◽  
Cell Recording ◽  
Rabbit Sinoatrial Node ◽  
Best Fit ◽  
Maximum Conductance

A tetrodotoxin (TTX)-sensitive Na+ current (iNa) was investigated in single pacemaker cells after 1-4 days in culture. Ruptured-patch and perforated-patch whole cell recording techniques were used to record iNa and spontaneous electrical activity, respectively. For seven cells exposed to 20 mM Na+ (22-24 degrees C) and held at -98 mV (25% of the channels inactivated), the uncorrected maximum iNa was -39 +/- 10 pA/pF at -29.1 +/- 2.4 (SE) mV, maximum conductance was 0.9 +/- 0.2 nS/pF (1.6 +/- 0.2 mS/cm2). Half-activation and inactivation potentials were -41.4 +/- 2.0 and -90.6 +/- 2.5 mV, and the corresponding slope factors were 6.0 +/- 0.4 and 6.4 +/- 0.6 mV. Inactivation and recovery from inactivation were best fit by sums of two exponentials. During action potential clamp, a TTX-sensitive compensation current accounted for 55% of the upstroke velocity. The results suggest that iNa contributes significantly to the action potential in some nodal pacemaker cells, and the characteristics of iNa are similar to those of atrial and ventricular myocytes.

scholarly journals Metabolic features of mouse and human retinas: rods vs. cones, macula vs. periphery, retina vs. RPE

2020 ◽  
Author(s):  
Bo Li ◽  
Ting Zhang ◽  
Wei Liu ◽  
Yekai Wang ◽  
Rong Xu ◽  
...  
Keyword(s):  
Aerobic Glycolysis ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Lipid Synthesis ◽  
Metabolic Stress ◽  
Tca Cycle ◽  
High Energy ◽  
Metabolic Dysfunction ◽  
Metabolic Demand ◽  
Energy Demands

AbstractPhotoreceptors, especially cones, which are enriched in the human macula, have high energy demands, making them vulnerable to metabolic stress. Metabolic dysfunction of photoreceptors and their supporting retinal pigment epithelium (RPE) is an important underlying cause of degenerative retinal diseases. However, how cones and the macula support their exorbitant metabolic demand and communicate with RPE is unclear. By profiling metabolite uptake and release and analyzing metabolic genes, we have found cone-rich retinas and human macula share specific metabolic features with upregulated pathways in pyruvate metabolism, mitochondrial TCA cycle and lipid synthesis. Human neural retina and RPE have distinct but complementary metabolic features. Retinal metabolism centers on NADH production and neurotransmitter biosynthesis. The retina needs aspartate to sustain its aerobic glycolysis and mitochondrial metabolism. RPE metabolism is directed toward NADPH production and biosynthesis of acetyl-rich metabolites, serine and others. RPE consumes multiple nutrients, including proline, to produce metabolites for the retina.

scholarly journals Mitochondrial Membrane Dynamics—Functional Positioning of OPA1

Antioxidants ◽  
2018 ◽  
Vol 7 (12) ◽  
pp. 186 ◽  
Author(s):  
Hakjoo Lee ◽  
Yisang Yoon
Keyword(s):  
Mitochondrial Membrane ◽  
Proteolytic Cleavage ◽  
Membrane Dynamics ◽  
Mitochondrial Morphology ◽  
Inner Membrane ◽  
Mitochondrial Inner Membrane ◽  
Functional Differences ◽  
New Information ◽  
New Development

The maintenance of mitochondrial energetics requires the proper regulation of mitochondrial morphology, and vice versa. Mitochondrial dynamins control mitochondrial morphology by mediating fission and fusion. One of them, optic atrophy 1 (OPA1), is the mitochondrial inner membrane remodeling protein. OPA1 has a dual role in maintaining mitochondrial morphology and energetics through mediating inner membrane fusion and maintaining the cristae structure. OPA1 is expressed in multiple variant forms through alternative splicing and post-translational proteolytic cleavage, but the functional differences between these variants have not been completely understood. Recent studies generated new information regarding the role of OPA1 cleavage. In this review, we will first provide a brief overview of mitochondrial membrane dynamics by describing fission and fusion that are mediated by mitochondrial dynamins. The second part describes OPA1-mediated fusion and energetic maintenance, the role of OPA1 cleavage, and a new development in OPA1 function, in which we will provide new insight for what OPA1 does and what proteolytic cleavage of OPA1 is for.

scholarly journals Cardiac Pacemaker Cells Generate Cardiomyocytes from Fibroblasts in Long-Term Cultures

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Shigeki Kiuchi ◽  
Akino Usami ◽  
Tae Shimoyama ◽  
Fuminori Otsuka ◽  
Sachiko Yamaguchi ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Cardiac Fibroblasts ◽  
Cluster Formation ◽  
Cardiac Pacemaker ◽  
Pacemaker Cells ◽  
Intracellular Ca ◽  
Specific Proteins ◽  
Cell Densities

Abstract Because cardiomyocyte generation is limited, the turnover of cardiomyocytes in adult heart tissues is much debated. We report here that cardiac pacemaker cells can generate cardiomyocytes from fibroblasts in vitro. Sinoatrial node cells (SANCs) were isolated from adult guinea pig hearts and were cultured at relatively low cell densities. Within a week, a number of fibroblast-like cells were observed to gather around SANCs, and these formed spontaneously beating clusters with cardiomyocyte structures. The clusters expressed genes and proteins that are characteristic of atrial cardiomyocytes. Pharmacological blocking of pacemaker currents inhibited generation of action potentials, and the spontaneous beating were ceased by physically destroying a few central cells. Inhibition of beating during culture also hampered the cluster formation. Moreover, purified guinea pig cardiac fibroblasts (GCFs) expressed cardiac-specific proteins in co-culture with SANCs or in SANC-preconditioned culture medium under electrical stimulation. These results indicate that SANCs can generate cardiomyocytes from cardiac fibroblasts through the influence of humoral factor(s) and electrophysiological activities followed by intracellular Ca2+ oscillations. This potential of SANCs to generate cardiomyocytes indicates a novel mechanism by which cardiomyocytes turns over in the vicinity of pacemaker cells and could be exploited in the development of strategies for cardiac regenerative therapy in adult hearts.

Intracellular Ca2+ Release Sparks Atrial Pacemaker Activity

Physiology ◽  
2001 ◽  
Vol 16 (3) ◽  
pp. 101-106 ◽  
Author(s):  
Stephen L. Lipsius ◽  
Jörg Hüser ◽  
Lothar A. Blatter
Keyword(s):  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Right Atrium ◽  
Pacemaker Activity ◽  
Transport Mechanisms ◽  
Electrical Excitation ◽  
Pacemaker Cells ◽  
Pacemaker Function ◽  
Intracellular Ca ◽  
The Right

Electrical excitation of the mammalian heart originates from specialized pacemaker cells in the right atrium. Pacemaker activity depends on multiple ion channels and transport mechanisms that reside primarily within the plasma membrane. However, recent evidence indicates that intracellular Ca2+ release from the sarcoplasmic reticulum also contributes importantly to atrial pacemaker function.

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