Simulated Microgravity and Hypergravity Affect the Expression Level of Soluble Guanylate Cyclase, Adenylate Cyclase, and Phosphodiesterase Genesin Rat Ventricular Cardiomyocytes

Ion channels activity is regulated through soluble guanylate cyclase (sGC) and adenylate cyclase (AC) pathways, while phosphodiesterases (PDE) control the intracellular levels of cAMP and cGMP. Here we applied RNA transcriptome sequencing to study changes in the gene expression of the sGC, AC, and PDE isoforms in isolated rat ventricular cardiomyocytes under conditions of microgravity and hypergravity. Our results demonstrate that microgravity reduces the expression of sGC isoform genes, while hypergravity increases their expression. For a subset of AC isoforms, gene expression either increased or decreased under both microgravity and hypergravity conditions. The expression of genes encoding 10 PDE isoforms decreased under microgravity, but increased under hypergravity. However, under both microgravity and hypergravity, the gene expression increased for 7 PDE isoforms and decreased for 3 PDE isoforms. Overall, our findings indicate specific gravity-dependent changes in the expression of genes of isoforms associated with the studied enzymes.

Identification of RNA reads encoding different channels in isolated rat ventricular myocytes and the effect of cell stretching on L-type Ca2+current

BACKGROUND

The study aimed to identify transcripts of specific ion channels in rat ventricular cardiomyocytes and determine their potential role in the regulation of ionic currents in response to mechanical stimulation. The gene expression levels of various ion channels in freshly isolated rat ventricular cardiomyocytes were investigated using the RNA-seq technique. We also measured changes in current through CaV1.2 channels under cell stretching using the whole-cell patch-clamp method.

RESULTS

Among channels that showed mechanosensitivity, significant amounts of TRPM7, TRPC1, and TRPM4 transcripts were found. We suppose that the recorded L-type Ca2+ current is probably expressed through CaV1.2. Furthermore, stretching cells by 6, 8, and 10 μm, which increases ISAC through the TRPM7, TRPC1, and TRPM4 channels, also decreased ICa,L through the CaV1.2 channels in K+ in/K+ out, Cs+ in/K+ out, K+ in/Cs+ out, and Cs+ in/Cs+ out solutions. The application of a nonspecific ISAC blocker, Gd3+, during cell stretching eliminated ISAC through nonselective cation channels and ICa,L through CaV1.2 channels. Since the response to Gd3+ was maintained in Cs+ in/Cs+ out solutions, we suggest that voltage-gated CaV1.2 channels in the ventricular myocytes of adult rats also exhibit mechanosensitive properties.

CONCLUSIONS

Our findings suggest that TRPM7, TRPC1, and TRPM4 channels represent stretch-activated nonselective cation channels in rat ventricular myocytes. Probably the CaV1.2 channels in these cells exhibit mechanosensitive properties. Our results provide insight into the molecular mechanisms underlying stretch-induced responses in rat ventricular myocytes, which may have implications for understanding cardiac physiology and pathophysiology.

Simulated Microgravity Changes the Number of Mechanically Gated and Mechanosensitive Ion Channels Genes Transcripts in Rat Ventricular Cardiomyocytes

The mechanoelectrical feedback in the heart is based on the work of mechanically gated (MGCs) and mechanosensitive (MSCs) channels. Since microgravity alters the heart's morphological and physiological properties, we hypothesized that the expression of both MGCs and MSCs would be affected. We employed RNA transcriptome sequencing to investigate changes in the gene transcript levels of MGCs and MSCs in isolated rat ventricular cardiomyocytes under control conditions and in a simulated microgravity environment. For the first time, our findings demonstrated that simulated microgravity induces alterations in the gene transcript levels of specific MGCs, such as TRPM7, TRPV2, TRPP1, TRPP2, Piezo1, TMEM63A, TMEM36B, and known MSCs, including K2P2.1, K2P3.1, Kir6.1, Kir6.2, NaV1.5, CaV1.2, KV7.1. However, other voltage-gated channels and channels lacking a voltage sensor remained unaffected. These findings suggest that the altered expression of MGCs and MSCs could lead to changes in the net currents across the membrane, ultimately impacting the heart's function.

Hypergravity Increases the Number of Gene Transcripts of Mechanically Gated and Mechanosensitive Ion Channels in Rat Ventricular Cardiomyocytes

Since hypergravity changes the morphological and physiological properties of the heart, it was assumed that the expression of ion channels that respond to cell stretching or compressing, mechanically gated channels (MGC) and mechanosensitive channels (MSC), would be affected. Using RNA transcriptome sequencing, the change in the number of transcripts for MGC and MSC genes was studied in isolated rat ventricular cardiomyocytes under 4g hypergravity for 5 days. It was shown for the first time that hypergravity induces changes in the number of transcripts of MGC genes: an increase for TRPC1, TRPC3, TRPM7, TRPP1 (PKD1), TRPP2 (PKD2), TMEM63A, TMEM63B, but a decrease for TRPV2, Piezo1, Piezo2. The number of MSC gene transcripts increases: TREK-1, Kir6.2, Nav1.5, Cav1.2, Cav1.3, Kv7.1, and Kv1.2. This potentially leads to an increase in the expression of MGC and MSC proteins leading to an increase in the net current and, as a result, pathological changes in the heart function.

The role of activation of two different sGC binding sites by NO-dependent and NO-independent mechanisms in the regulation of SACs in rat ventricular cardiomyocytes

The mechanoelectrical feedback (MEF) mechanism in the heart that plays a significant role in the occurrence of arrhythmias, involves cation flux through cation nonselective stretch-activated channels (SACs). It is well known that nitric oxide (NO) can act as a regulator of MEF. Here we addressed the possibility of SAC's regulation along NO-dependent and NO-independent pathways, as well as the possibility of S-nitrosylation of SACs. In freshly isolated rat ventricular cardiomyocytes, using the patch-clamp method in whole-cell configuration, inward nonselective stretch-activated cation current I_SAC was recorded through SACs, which occurs during dosed cell stretching. NO donor SNAP, α1-subunit of sGC activator BAY41-2272, sGC blocker ODQ, PKG blocker KT5823, PKG activator 8Br-cGMP, and S-nitrosylation blocker ascorbic acid, were employed. We concluded that the physiological concentration of NO in the cell is a necessary condition for the functioning of SACs. An increase in NO due to SNAP in an unstretched cell causes the appearance of a Gd³⁺ -sensitive nonselective cation current, an analog of I_SAC , while in a stretched cell it eliminates I_SAC . The NO-independent pathway of sGC activation of α subunit, triggered by BAY41-2272, is also important for the regulation of SACs. Since S-nitrosylation inhibitor completely abolishes I_SAC , this mechanism occurs. The application of BAY41-2272 cannot induce I_SAC in a nonstretched cell; however, the addition of SNAP on its background activates SACs, rather due to S-nitrosylation. ODQ eliminates I_SAC , but SNAP added on the background of stretch increases I_SAC in addition to ODQ. This may be a result of the lack of NO as a result of inhibition of NOS by metabolically modified ODQ. KT5823 reduces PKG activity and reduces SACs phosphorylation, leading to an increase in I_SAC . 8Br-cGMP reduces I_SAC by activating PKG and its phosphorylation. These results demonstrate a significant contribution of S-nitrosylation to the regulation of SACs.

Gadolinium as an Inhibitor of Ionic Currents in Isolated Rat Ventricular Cardiomyocytes

The whole-cell patch-clamp technique was used to examine the effect of gadolinium Gd³⁺ (a non-specific blocker of mechanically gated current I_MGCh, a component of late current I_L) on ionic currents in insolated rat ventricular cardiomyocytes alone and in combination with the blockers of L-type calcium currents (I_CaL) nifedipine (10 μM) or verapamil (1 μM). In K⁺_in/K⁺_out or Cs⁺_in/Cs⁺_out media, blockade of I_CaL produced no effect on I_L at negative potentials, but inhibited I_L at positive ones. In K⁺_in/K⁺_out medium, Gd³⁺ (5 μM) decreased the net persistent current (I_np) at -45 mV from 198.6±6.4 to 96.7±9.5 pA over 15 min. Gd³⁺ alone or in combination with I_CaL blockers shifted the reversal potential of I_L to more negative values. At negative potentials, Gd³⁺ decreased I_K1 and inward current including I_MGCh. At positive potentials, Gd³⁺ alone or in combination with I_CaL blockers decreased I_L. When applied for 15 min in Cs⁺_in/Cs⁺_out medium at -45 mV, Gd³⁺ produced no effect on net current and inward and outward components of I_L. Thus, Gd³⁺ can be viewed as a specific blocker of I_MGCh only in Cs⁺ medium.

[Correlations of IL-18 and IL-6 with sodium consumption in patients with arterial hypertension and diabetes mellitus]

AIM

To determine correlations of AH-associated interleukins (IL-18, IL-6) with sodium consumption in AH patients with and without DM.

MATERIALS AND METHODS

The study included AH patients with and without DM (n=63) who were managed at the Municipal Clinic #64, Moscow Department of Health Care, Branch 1. Plasma levels of IL-6 and IL-18 were measured using ELISA kits (Bender Med-Systems). Salt consumption was determined using a Charlton: SaltScreener questionnaire. Statistical analyses were performed using the Statistica 10.0 software.

RESULTS

Four groups were formed: Group 1, grade 2 AH and DM (n=19); Group 2, grade 2 AH and no DM (n=4); Group 3, grade 3 AH and no DM (n=28); and Group 4, grade 3 AH and DM (n=12). Group 2 was small and was excluded from further analysis due to impossibility of statistical treatment. All patients consumed more than 6 g of salt per day (approximately 10 g). Analysis of intergroup differences in selected parameters showed differences between groups in levels of cholesterol, triglycerides, LDL, and GFR. The following correlations were identified in the groups: Group 1, positive correlation of IL-18 with sodium consumption (r=0.65) and CRP level (r=0.52) and of IL-6 with LDL level (r=0.48); Group 3, positive correlation of IL-18 with IL-6 (r=0.66) and of IL-6 with CRP (r=0.52); Group 4, positive correlation of IL-18 with GFR (r=0.82) and of IL-6 with waist circumference (WC) (r=0.84) and IL-6 (r=0.73).

CONCLUSION

Patients consuming more than 6 g of salt daily (approximately 10 g) with AH and DM had more pronounced inflammation, which promoted progression of kidney disease.

Discrete Stretch Eliminates Electrophysiological Dose-Dependent Effects of Nitric Oxide Donor SNAP in Rat Atrium

Depolarization of cardiomyocytes triggered by stretch and activation of mechanically gated ion channels can lead to serious arrhythmias. However, stretch-induced signaling activating these channels remain little studied. This study tested the hypothesis on implication of NO in shaping the electrical abnormalities provoked by stretch of the right atrial myocardium in rat via a mechanism engaging a signaling cascade, where NO plays a significant role. This approach showed that in isolated right atrial preparation, NO donor SNAP induces the electrical abnormalities similar to those provoked by stretch, and the latter results from activation of NO synthase.

Kinetics of Mechanical Stretch-Induced Nitric Oxide Production in Rat Ventricular Cardiac Myocytes

Discrete mechanical stretch of isolated spontaneously contracting cardiac myocytes was employed to examine the kinetics of NO production in these cells. NO oscillations were detected with fluorescent dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate. The mechanisms underlying stretch-induced changes in NO concentration remain unclear and further studies are needed to evaluate the role of NO oscillation in the regulation of cardiomyocyte function.

Cytokine Effects on Mechano-Induced Electrical Activity in Atrial Myocardium

The role of cytokines as regulators of stretch-related mechanisms is of special importance since mechano-sensitivity plays an important role in a wide variety of biological processes. Here, we elucidate the influence of cytokine application on mechano-sensitivity and mechano-transduction. The atrial myocardial stretch induces production of interleukin (IL)-2, IL-6, IL-13, IL-17A, and IL-18 with exception of tumor necrosis factor α (TNF-α), IL-1β, and vascular endothelial growth factor B (VEGF-B). Positive ionotropic effect was specific for VEGF-B, negative ionotropic effects were specific for TNF-α, IL-1β, IL-2, IL-6, IL-13, IL-17A and IL-18, while IL-1α doesn't show direct ionotropic effect. The IL-2, IL-6, IL-17A, IL-18, and VEGF-B cause elongation of the APD, in comparison with the reduced APD caused by the IL-13. The TNF-α, IL-1β, and IL-18 influences L-type Ca²⁺ channels, IL-2 has an inhibitory effect on the fast Na⁺ channels while IL-17A and VEGF-B were specific for Kir channels. With exception of the IL-1α, IL-2, and VEGF-B, all analyzed cytokines include nitric oxide dependent signaling with resultant combined effects on mechano-gated and Ca²⁺ channels. The relationships between these pathways and the time-dependence of their activation are of important considerations in the evaluation of cytokine-induced electrical abnormality, specific for cardiac dysfunctions. In general, the discussion presented in this review covers research devoted to counterbalance between different cytokines in the regulation of stretch-induced effects in rat atrial myocardium.

ABBREVIATIONS

APs: action potentials; APD25: action potential durations to 25% of re-polarization; APD50: action potential durations to 50% of repolarization; APD90: action potential durations to 90% of repolarization; MGCs: mechanically gated channels.

Serum interleukin-6: Association with circulating cytokine serum levels in patients with sinus arrhythmia and patients with coronary artery disease

In this study, we were focused on the differences between certain circulating cytokine levels in patients with or without sinus arrhythmia, according to the median IL-6 level. All patients were stable with regards to symptoms and therapy for at least one month prior to the measurements conducted within this study.Exclusion criteria were: patients with sleep apnea, asthma, respiratory insufficiency of any genesis, active infection, allergy, inflammatory diseases, cancer, diabetes of any type and treatment with anti-inflammatory drugs. The study was approved by the Institutional Review Board. All recruited patients gave their verbal and written consent for participation in the study. The study group consisted of 74 patients divided into two groups: with (38) and without sinus arrhythmia but with diagnosed coronary artery disease (36). Sinus arrhythmia was confirmed by 24h Holter monitoring. From all test parameters only cytokines IL-2, IL-8, IL-10, IL-17 and IL-18, showed statistically significant increasing in patients with statistically higher IL-6 levels. It is possible that IL-6 may not be a marker for the selection of patients with sinus arrhythmia or coronary artery disease. The findings indicate that IL-6 represents a reliable indicator for increased expression of IL-2, IL-8, IL-10, IL-17 and IL-18 in patients with sinus arrhythmia or coronary artery disease. Further studies in a large number of patients would be necessary to confirm our observations.

Effects of vascular endothelial growth factor-b on the bioelectric activity of rat atrial myocardium under normal conditions and during gradual stretching

Using a microelectrode technique we studied the effects of vascular endothelial growth factor-B on the activity of rat atrial myocardium under normal conditions and after gradual stretching of the tissue. It was shown that vascular endothelial growth factor-B increased duration of the action potential only at the level of 90% re-polarization. Effects on the frequency and force of contraction were absent. The repetition frequency of the action potentials did not change. Close observation of the vascular endothelial growth factor-B-induced mechanisms and stretch-induced alteration in action potential durations to 90% of repolarization, confirmed the existence of a link between the examining growth factor-B and stretch induced mechanisms.

[Influence of interleukin-13 on bioelectrical activity of rat atrial cardiomyocytes in normal and stretch conditions]

We studied the effect of anti-inflammatory ininterleukin-13 (IL-13; 50 ng/ml) on bioelectrical activity of rat atrial cardiomyocytes under control conditions and on the background of stretch by means of microelectrode technique. IL-13 did not lead to alterations of the resting membrane potential and action potential amplitude during 35 minutes. However APD25, APD50, APD90 in 50% of cases significantly decreased, while in other 50% of cases it increased. In case when IL-13 decreased APD cellular stretch by 1.7 mN caused an increase in APD frequency by 120% and caused decrease in APD25, APD50, APD90, which happened on the background of modest cellular depolarization in the range of 5 mV. When IL-13 increased APD, tissue stretching just by 0.8 mN caused depression of the frequency by 10% and increase in APD25, APD50, APD90. This happened on the background of small cellular depolarization.