Molecular background of impairments in skeletal muscle of heart failure patients

Background

Heart failure (HF) is characterised by systematic inflammation and chronic metabolic dysregulation. HF enhances the release of pro-inflammatory cytokines, induces activation of the complement system, production of autoantibodies, and over-expression of the major histocompatibility (MHC) complex class II molecules. It is known that skeletal muscles are exposed to the immunologic injury in disease; and muscle tissue appeared to be affected by HF leading to the muscle weakness and exercise intolerance development. However, molecular abnormalities occurring in HF patients' muscles and the mechanisms underlying its development are not clarified.

Purpose

To understand the molecular mechanisms underlying skeletal muscle immune and non-immune impairments in HF.

Methods

8 health donors and 5 HF patients with reduced ejection fraction (NYHA Class II and III) were enrolled in this study in accordance with the principles under the Declaration of Helsinki (1989). mRNA of skeletal muscle biopsies of gastrocnemius lateralis were sequenced on Illumina HiSeq. RNA-seq analysis was performed using STAR with reference genome GRCh38 and featureCounts program; differentially expressed genes (DEGs) were assessed using R package DESeq2 with FDR=0.01 and log2 fold change (l2fc) >1.5 filter; pathway analysis was performed using clusterProfiler in R (FDR=0.01).

Results

1404 differentially expressed genes distinguish muscles of HF patients and controls. Among upregulated genes there are different classical MHC molecules and specific one HLA-G (l2fc=2) that has been previously shown appeared in muscles under autoimmune myopathies, and potentially protect them. Unregulated DEGs were responsible for the activation of many molecular immunological pathways: type I interferon signaling pathway (16 DEGs out of total 89), regulation of T cell proliferation (14/153), neutrophil degranulation (31/485), granulocyte differentiation (7/32), negative regulation of viral process (11/53), that indicates about specific inflammatory response in HF muscles. Response to hypoxia (22/314) and gluconeogenesis pathways (12/87) were also activated. Downregulated genes include SLC5A1 (l2fc=−4) sodium glucose cotransporter; NRP3 (l2fc=−4) that plays a role in modulating intravascular volume and vascular tone; MMP1 (l2fc=−13) involved in the breakdown of extracellular matrix; the expression of many genes responsible for DNA-repair (44/534) and cilium assembly (34/366) was also suppressed.

Conclusion

Transcriptome analysis shows immunological and non-immunological alterations in HF skeletal muscles and provides the information about molecular mechanisms of its development.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Russian Science Foundation grant

THE ROLE OF LMNA MUTATIONS IN MYOGENIC DIFFERENTIATION OF PRIMARY SATELLITE CELLS AND C2C12 CELLS

Nuclear lamins form nuclear lamina localized under the inner nuclear membrane. It was previously considered that the nuclear lamina predominantly plays a structural role, however, its involvement have been recently described in the regulatory processes such as chromatin organization and gene transcription. It is known that mutations in the LMNA gene lead to the development of a large number of diseases, laminopathies, which mainly affect mesenchymal tissue. Nowadays, the mechanisms by which the lamina can regulate cell differentiation remain incompletely understood. In the present work, we have studied the effect of LMNA gene mutations on the process of muscle differentiation of primary satellite cells and Ñ2Ñ12 cell line. The genome of satellite cells and Ñ2Ñ12 cell line was modified by the introduction of lentiviral constructs encoding LMNA G232E associated with the development of muscular dystrophy Emery—Dreyfus and LMNA R571S associated with the development of dilated cardiomyopathy. The morphology of the cells was estimated using immunofluorescence, the expression level of myogenic genes were analyzed by qPCR. We have shown that the analyzed mutations reduce the ability of cells to differentiate, to fuse and to form myotubes. We have suggested that it is due to enhanced expression of markers at the early stages and to reduced expression markers at the late stages of myogenesis. Therefore, mutations in nuclear lamins can influence the process of muscle differentiation.

[Nuclear lamins regulate osteogenic differentiation of mesenchymal stem cells]

Nuclear lamins are the major proteins of nuclear envelope and provide the strength of nuclear membrane as well as the interaction of extra-nuclear structures with components of cell nucleus. Recently, it became clear that lamins not only play a structural role in the cell, but could also regulate cell fate, for example lamins could influence cell differentiation via interaction with components of the Notch signaling pathway. Human mutations in LMNA, encoding lamin A/C lead to diseases commonly referred to as laminopathies. Different mutations cause tissue specific phenotypes that affect predominantly a tissue of mesenchymal origin. The nature of this phenomenon, as well as the mechanisms by which lamins regulate cell differentiation remain poorly understood. The aim of this study was to investigate the effect of different mutations of the LMNA on human mesenchymal stem cell (MSC) osteogenic differentiation, and to explore a possible interaction of lamins and Notch signaling pathway. We modified human MSC with mutant LMNA bearing known mutations with tissue specific phenotype associated with different laminopathies. We have shown that mutations associated with different diseases have different effects on the efficiency of MSC osteogenic differentiation and on the expression of specific osteogenic markers SPP1, IBSP and BGLAP. We have also shown that one of the mechanisms involved in the regulation of MSC differentiation may be an interaction of lamins A/C with components of Notch signaling.

[Comparative assessment of different approaches for obtaining terminally differentiated muscle cells]

Relevant cell model is essential to study pathogenesis of muscle disorders. However, in the field of muscle research there is no ultimate cell line considered as a standard for studying muscular and neuromuscular diseases. Standard cell line claimed to be well differentiated in muscle lineage, be morphological and physiological similar to mature muscle cells and be easily genetically modified. Therefore, the goal of our study was to pick up available and fruitful cell model of muscle differentiation, that could be further applied for examination of muscular disorder pathogenesis in vitro. We characterized human mesenchymal stem cells (MSC), mature murine muscle fibers and primary murine satellite cells. It has been shown that MSC have very small capacity to myogenic differentiation; moreover, they were able to differentiate only in presence of C2C12 cells. Lentiviral transduction exhibited rather high toxic effect on primary myofibers, and positively transduced cells were not able to response to electrical stimulation, i. e. were functionally inactive. Satellite cells turned out to be the most fruitful cell model since they were easily transduced via lentiviruses and rapidly formed myotubes in differentiation media. Functional analysis of obtained myotubes has confirmed their ability to react to electrical and chemical stimulations; besides, potassium and calcium channels availability has been also demonstrated via patch-clump technique. Taken together, these results imply that satellite cells are the most promising cell line for further experiments aimed at exploring the molecular pathways of muscle pathologies.

[Optional protocols of hematopoietic stem cell expansion in vitro]

Hematopoietic stem cells (HSC) effectively and continuously renew a full spectrum of blood cell populations. Bone marrow and umbilical cord blood stem cells transplantation (SCT) restore hematopoietsis, when used in various hematological and oncohematological disorders in adults and children. However, wider clinical application of effective SCT-based approaches is limited by the low number of the primitive HSC in the available biospecimens. Development of effective protocols for HSC expansion in vitro is therefore necessary. In this review, a concept of bone marrow hematopoiesis niche being a complex cellular system is discussed; a comparative analysis of various methods for HSC expansion in vitro is provided. The review is illustrated by the authors own data supporting application of various feeder cell types for human HSC expansion in vitro.

[Neurogenic potential of human mesenchymal stem cells isolated from bone marrow, adipose tissue and endometrium: a comparative study]

Mesenchymal stem cells (MSCs) can be isolated from many adult tissue sources. These cells are a valuable substrate in cell therapy for many diseases and injuries. Different types of MSCs vary in plasticity. We performed a comparative study of the neurogenic potential of three types of human MSCs derived from bone marrow (BMSCs), subcutaneous adipose tissue (ADSCs) and endometrium (isolated from the menstrual blood) (eMSCs). It was shown that all three types of MSC cultures demonstrate multipotent plasticity and predisposition to neurogenesis, based on the expression of pluripotency markers SSEA-4 and neuronal precursors' markers nestin and beta-III-tubulin. Further analysis revealed the transcription of the neuronal marker MAP2 and neurotrophin-3 in undifferentiated BMSCs and ADSCs. Additionally, a significant basal level of synthesis of brain-derived neurotrophic factor (BDNF) in eMSC culture was also observed. Stimulation of neural induction with such agents as 5-azacytidine, recombinant human basic fibroblast growth factor (bFGF), recombinant human epidermal growth factor (EGF), a recombinant human fibroblast growth factor 8 (FGF8), morphogen SHH (sonic hedgehog), retinoic acid (RA) and isobutyl-methyl-xanthine (IBMX), showed further differences in the neurogenic potential of the MSCs. The components of the extracellular matrix, such as Matrigel and laminin, were also the important inducers of differentiation. The most effective neural induction in BMSCs proceeded without the RA participation while the cells pretreated with 5-azacytidine. In contrary, in the case of eMSCs RA was a necessary agent of neural differentiation as it stimulated the transcription of neurotrophin-4 and the elevation of secretion level of BDNF. The use of laminin as the substrate in eMSCs appeared to be critical, though an incubation of the cells with 5-azacytidine was optional. As far as ADSCs, RA in combination with 5-azacytidine caused the elevation of expression of MAP2, but reduced the secretion of BDNF. Thus, the effect of RA on neural differentiation of ADSCs in ambiguous and, together with the study of its signaling pathways in the MSCs, requires further research. The therapeutic effect of transplanted MSCs is commonly explained by their paracrine activity. The high basal level of BDNF synthesis in the eMSCs, along with their high proliferative rate, non-invasive extraction and neural predisposition, is a powerful argument for the use of the intact eMSCs as a substrate in cell therapy to repair nerve tissue.

[Lamin A/C mutations change differentiation potential of mesenchymal stem cells]

Mutations in lamin A/C gene (LMNA) lead to development of severe disorders--laminopathies. Unlike most other types of intermediate filaments, where the pathological effect of mutations is tightly linked to alteration of mechanical and integrative functions, the detailed mechanism of lamin mutations is still unclear and possibly involves the alteration of nuclear signaling and transcriptional processes. Since the mesenchymal lineage tissues such as myocardium, skeletal muscle, adipose and bone tissues are mostly affected in laminopathies, the role of lamin A/C in differentiation process of mesenchymal stem cells has been assumed. The aim of the study was to estimate the effect of LMNA mutations of differentiation of mesenchymal stem cells into adipose lineages. In vitro mitagenesis was performed on wild type LMNA gene incorporated in a lentiviral vector. Several previously described mutations in LMNA were used, each associated with a certain phenotype. Adipose-derived mesenchymal stem cells from healthy donors were transduced with lentiviruses bearing either wild-type or mutant LMNA. Cells were then induced to adipose differentiation. We show that mutant LMNA/C promotes differentiation capacity of mesenchymal stem cells as seen by morphological changes and by expression of specific adipose markers.

Mammalian bufadienolide is synthesized from cholesterol in the adrenal cortex by a pathway that Is independent of cholesterol side-chain cleavage

An increasing body of evidence suggests that an endogenous mammalian bufadienolide (BD) may be involved in the regulation of Na(+),K(+)-ATPase activity and the pathogenesis of arterial hypertension. We developed a purification scheme for marinobufagenin (MBG), an amphibian cardiotonic BD, and applied it to purify and characterize material in human plasma, culture medium conditioned by Y-1 adrenocortical cells, and rat adrenal tissue. MBG immunoreactivity purified from plasma and measured by ELISA showed important similarities (chromatography and antibody cross-reactivity) to material secreted into cell culture medium by Y-1 cells. This observation indicates that circulating mammalian BD may have an adrenocortical origin. Release of mammalian BD from adrenocortical cells grown in the absence of exogenous cholesterol was reduced by treatment of cultures with mevastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor. Supplementation of the serum and cholesterol-free cell culture medium with the LDL fraction of human plasma increased the production of MBG material in the presence of mevastatin, supporting its origin from cholesterol. We used Y-1 cell lines transfected with genes shown to inhibit steroidogenesis through cholesterol side-chain cleavage (Y-1/DAX and Y-1/RIAB) to investigate the dependence of MBG biosynthesis on side-chain cleavage. Our results indicate that the mammalian BD is synthesized in the adrenal cortex from cholesterol and shares important similarities with the amphibian BD MBG, that its biosynthesis is independent of transfer of cholesterol to the side-chain cleavage enzyme complex mediated by steroidogenic acute regulatory protein, and that neither cAMP nor protein kinase A appears to be a critical component of the pathway controlling its biosynthesis.

Cicletanine reverses vasoconstriction induced by the endogenous sodium pump ligand, marinobufagenin, via a protein kinase C dependent mechanism

RATIONALE

Cicletanine (CIC), an anti-hypertensive compound with direct vascular and natriuretic actions, is especially effective in salt-sensitive hypertension, in which dysregulation of the sodium pump plays an important pathogenic role, and digitalis-like cardiotonic steroids contribute to increased vascular tone. The purpose of the present study was to investigate whether, and by what mechanisms, cicletanine antagonizes the vasoconstrictor effects of cardiotonic steroids in isolated human arteries.

METHODS

The effects of cicletanine on vascular tone were studied in isolated, endothelium-denuded rings of 2nd-3rd-order branches of human mesenteric arteries pre-contracted with bufodienolide marinobufagenin (MBG), an Na/K-ATPase inhibitor, or endothelin-1 (ET-1). Na/K-ATPase activity was measured in sarcolemmal membranes from the mesenteric artery. Activity of rat brain protein kinase C (PKC) was measured using the PepTag phosphorylation assay.

RESULTS

MBG and ET-1 both induced sustained vasoconstriction in human mesenteric artery rings, and cicletanine relaxed rings pre-contracted with either MBG (EC50 = 11 +/- 2 micromol/l) or ET-1 (EC50 = 6.4 +/- 1.1 micromol/l). Although 8-Br-cGMP (100 micromol/l) caused complete vasorelaxation of arterial rings pre-contracted with ET-1, it did not affect the MBG-induced vasoconstriction. An activator of PKC, phorbol diacetate (PDA) (50 nmol/l), attenuated CIC-induced vasorelaxation of mesenteric artery rings pre-contracted with MBG (EC50 > 100 micromol/l), but not rings pre-contracted with ET-1 (EC50 = 6.5 +/- 1.2 micromol/l). In mesenteric artery sarcolemma, 100 nmol/l MBG inhibited the Na/K-ATPase by 68 +/- 5% and cicletanine (100 micromol/l) attenuated this Na/K-ATPase inhibition by 85 +/- 6%. In the PepTag PKC assay, cicletanine produced a concentration-dependent inhibition of rat brain PKC activity (IC50 45 +/- 11 micromol/l). In the presence of 50 nmol/l PDA, 100 micromol/l cicletanine did not antagonize the Na/K-ATPase inhibition by MBG, and did not inhibit the PKC from rat brain.

CONCLUSIONS

Cicletanine antagonizes vasoconstriction induced by Na/K-ATPase inhibition via a PKC-dependent mechanism that does not involve inhibition of cyclic GMP phosphodiesterase (cGMP-PDE). This mechanism of action may be relevant to the greater potency of cicletanine in salt-sensitive hypertension in which plasma levels of endogenous digitalis-like cardiotonic steroids are elevated. Our findings also suggest that PKC is an important factor for cardiotonic steroid-Na/K-ATPase interactions on the vascular tone, and is therefore a potential target for therapeutic intervention in hypertension.

Circulating bufodienolide and cardenolide sodium pump inhibitors in preeclampsia

OBJECTIVE

To determine plasma levels of the endogenous bufodienolide Na+/K+ ATPase inhibitor, marinobufagenin-like factor (MBG), in normotensive pregnancy and in preeclampsia, to compare changes of MBG with that of ouabain-like compound (OLC), and to characterize the purified MBG immunoreactive factor from preeclamptic plasma.

DESIGN AND METHODS

Consecutive sample study. The levels of MBG and OLC compounds were measured in extracted plasma by solid phase fluoroimmunoassays. MBG and ouabain immunoreactive materials were partially purified from preeclamptic plasma via reverse-phase high-performance liquid chromatography (HPLC) and studied for their ability to cross react with MBG and ouabain antibodies, and to inhibit the Na+/K+ ATPase from human mesenteric arteries. Vasoconstrictor effect of authentic MBG was studied in isolated rings of human umbilical arteries.

RESULTS

In 11 nonpregnant control individuals, plasma concentrations of MBG and OLC were 0.190+/-0.04 nmol/l and 0.297+/-0.037 nmol/l, respectively. In the third trimester of noncomplicated pregnancy (n = 6), plasma MBG increased (0.625+/-0.067 nmol/l, P<0.05), and OLC did not (0.32+/-0.07 nmol/l). In 15 patients with preeclampsia, plasma levels of both MBG and OLC increased dramatically (2.63+/-0.10 nmol/l and 0.697+/-0.16 nmol/l, respectively, P<0.01 versus both control groups). When fractionated by reverse phase HPLC, OLC was eluted by 18% acetonitrile, and MBG by 48% acetonitrile. Serially diluted samples of MBG and OLC immunoreactive materials from HPLC fractions reacted with MBG and ouabain antibody in solid phase immunoassay in a concentration dependent fashion. Authentic MBG caused contractile responses of isolated rings of human mesenteric arteries in a concentration-dependent manner. Similarly to the authentic MBG, HPLC purified MBG immunoreactive material from preeclamptic plasma inhibited Na+/K+ ATPase purified from human mesenteric artery.

CONCLUSIONS

Our observations demonstrate the coexistence of two endogenous cardiotonic steroids in preeclamptic plasma, a more polar OLC and a less polar MBG-like compound. Substantial increases in plasma OLC and MBG immunoreactivity in preeclampsia, along with the vasoconstrictor properties of authentic MBG and Na+,K+ ATPase inhibitory activity of human MBG immunoreactive factor, suggest, that in preeclampsia, plasma concentrations of MBG are enough to substantially inhibit the sodium pump in cardiovascular tissues, and are in accordance with the views attributing endogenous digitalis-like factors a pathogenic role in the preeclamptic hypertension.

Vasorelaxant effects of cicletanine and its (+)- and (-)-enantiomers in isolated human pulmonary arteries

The purpose of the study was to investigate, in isolated human pulmonary artery, the ability of cicletanine and its (-) and (+)-enantiomers to attenuate the endothelin-1 (Et-1) induced vasoconstriction, and to potentiate vasorelaxation (relative to plateau of the effect of Et-1) by sodium nitroprusside (SNP) and human atrial natriuretic peptide (ANP). In pulmonary artery rings, Et-1 induced a concentration-dependent vasoconstriction with median effective concentration (EC50 = 26+/-2.8 nmol/L. Pretreatment of the vessels with 100 micromol/L (+/-)-cicletanine reduced the effect of Et-1 (EC50 = 36+/-3.5 nmol/L; P < .01). (-)-enantiomer displayed greater capacity to antagonize the vasoconstrictor action of Et-1 (EC50 = 47+/-4.2 nmol/L) v (+)-enantiomer (EC50 = 29.9+/-6.5 nmol/L; P < .01). In arterial rings, precontracted with 10 nmol/L Et-1, ANP caused vasorelaxation (EC50 = 9.7+/-1.9 nmol/ L). The relaxant effect of ANP was potentiated by 100 micromol/L of (-)-(EC50 = 4.2+/-0.6 nmol/L; P < .01), but not (+)-cicletanine (EC50 = 7.6+/-0.7 nmol/L). Sodium nitroprusside relaxed pulmonary artery rings precontracted with 10 nmol/L Et-1 (EC50 = 41+/-11 nmol/L). The effect of SNP was potentiated by 10 micromol/L (+/-)-cicletanine (EC50 = 9.0+/-0.7 nmol/L; P < .05). The potentiating effect of 10 micromol/L (+)-cicletanine was weaker (EC50 = 7.9+/-1.8 nmol/L) than that of (-)-enantiomer (EC50 = 3.3+/-0.54 nmol/L; P < .05). The relaxant effect of SNP was not further potentiated by 100 micromol/L (+/-)-cicletanine. The present results demonstrate that, cicletanine antagonizes Et-1 induced vasoconstriction in an isolated human pulmonary artery and potentiates vasorelaxation by two guanylate cyclase activators, ANP and SNP. (-)-Cicletanine displays greater vasorelaxant activity v (+)-enantiomer.

Characterization of a urinary bufodienolide Na+,K+-ATPase inhibitor in patients after acute myocardial infarction

Recent evidence suggests the existence of several endogenous Na+,K+-ATPase inhibitors in mammals. Previously, we have shown that the amphibian Na+,K+-ATPase inhibitor marinobufagenin (3,5-dihydroxy-14,15-epoxy bufodienolide) acts as a vasoconstrictor in isolated rat and human arteries. Mammalian plasma was shown to contain marinobufagenin-like immunoreactive material, which is responsive to saline volume expansion. The present study describes purification of a bufodienolide, which is similar to marinobufagenin, from the urine of patients after acute myocardial infarction with the use of thin-layer chromatography and reverse-phase high-performance liquid chromatography (HPLC). The purified substance cross-reacted with marinobufagenin antibody, demonstrated maximal UV absorbance at 300 nm characteristic of bufodienolides, and eluted from HPLC columns with the same retention time as marinobufagenin. Mass spectrometry of purified material revealed the presence of a substance indistinguishable from amphibian marinobufagenin and having molecular mass of 400 D. The present studies show that one of the human digitalis-like factors may have a bufodienolide structure and is likely to represent marinobufagenin or its isomer, and they suggest a role for this substance in the pathogenesis of myocardial ischemia.

Endogenous marinobufagenin-like immunoreactive substance. A possible endogenous Na, K-ATPase inhibitor with vasoconstrictor activity

Vasoconstrictor and Na/K pump inhibitory properties of a bufodienolide Na/K-ATPase inhibitor, marinobufagenin, were studied in isolated rings of 2 to 3 order branches of human pulmonary arteries respectively. Marinobufagenin displayed concentration-dependent vasoconstrictor activity (0.01 to 10 mmol/L). In sarcolemma membranes prepared from pulmonary artery marinobufagenin inhibited Na/K-ATPase (IC50 = 50 nmol/L). In eight healthy male Caucasians, concentrations of marinobufagenin-like immunoreactive material in C-18 extracted plasma were 1.38 +/- 0.60 nmol/L. Twenty-four-hour urinary release of marinobufagenin-like immunoreactive material in eight healthy males was 1.20 +/- 0.95 nmol/day. Chloroform extract of human urine was fractionated using reverse-phase high-performance liquid chromatography (32% acetonitrile, Deltapak). The HPLC fraction coeluting with marinobufagenin in 7 min, cross reacted with antimarinobufagenin and antidigoxin, but not antiouabain antibody. These results demonstrate that human plasma and urine contains a bufodienolide vasoconstrictor EDLF, marinobufagenin-like immunoreactive Na,K pump inhibitor.

Plasma marinobufagenin-like and ouabain-like immunoreactivity during saline volume expansion in anesthetized dogs

OBJECTIVES

This study investigated effects of acute plasma volume expansion on plasma levels and urinary output of two endogenous Na,K-ATPase inhibitors, marinobufagenin-like and ouabain-like immunoreactive substances.

METHODS

Plasma volume was expanded for 3 h via intravenous saline infusion in three groups of anesthetized dogs--nontreated (n = 5); pretreated with rabbit antidigoxin (n = 5); and pretreated with rabbit antimouse (control) antibody (n = 4).

RESULTS

Plasma marinobufagenin-like immunoreactivity increased to 11.87 +/- 3.16 nmol.l-1 (vs. 0.30 +/- 0.16 nmol.l-1) within 10 min of volume expansion, in parallel with a 15% increase in LVdP/dt, then decreased to 2.21 +/- 0.59 nmol.l-1, and in 90 min increased to 11.8 +/- 2.8 nmol.l-1, in parallel with the maximal natriuretic response. Plasma concentrations of ouabain-like immunoreactive material were increased after 90 min of saline infusion (0.019 +/- 0.004 nmol.l-1 vs. 0.139 +/- 0.056 nmol.l-1). Pretreatment of the animals with antidigoxin antibody blocked the positive inotropic and reduced natriuretic response to volume expansion, and decreased the urinary release of marinobufagenin-like, but not ouabain-like, material.

CONCLUSIONS

These results show the presence of marinobufagenin-like immunoreactive substance in dog plasma and suggest that mammalian EDLF may have a bufodienolide nature. Endogenous marinobufagenin-like immunoreactive substance, which is likely to cross-react with antidigoxin antibody, is involved in the natriuretic and positive inotropic responses to plasma volume expansion.

Endogenous marinobufagenin-like immunoreactive factor and Na+, K+ ATPase inhibition during voluntary hypoventilation

In previous studies investigators found that conditioned hypoventilatory breathing potentiated a sodium-sensitive form of hypertension in dogs that was not mediated by sympathetic nervous system arousal. Our study investigated effects of 30 minutes of voluntary hypoventilation, maintained by a respiratory gas monitor and feedback procedure, in 16 normotensive humans of both sexes on (1) plasma concentrations of endogenous digitalis-like factors (ouabain-like and marinobufagenin-like immunoreactivity), (2) activity of erythrocyte Na+, K+ -ATPase, (3) inhibitory activity of plasma Na+, K+ -ATPase, and (4) blood pressure. Increased end tidal PCO2 (41 +/- 0.78 mm Hg versus 37.6 +/- 1.03 mm Hg) was associated with (1) an increase in plasma marinobufagenin-like immunoreactivity (1.23 +/- 0.47 versus 4.96 +/- 1.19 nmol/L), (2) an inhibition of Na+, K+ -ATPase in red blood cells (3.68 +/- 0.22 versus 2.15 +/- 0.25 mmol Pi/mL-1/h-1; P < .01), (3) increase in plasma Na+, K+ -ATPase inhibitory activity (34.9 +/- 4.0% versus 48.8 +/- 2.1%, P < .02), and (4) increases in systolic (112.4 +/- 2.6 versus 107.6 +/- 1.8 mm Hg) and diastolic (73.5 +/- 2.1 versus 68.8 +/- 2.1 mm Hg) blood pressures. Plasma levels of ouabain-like immunoreactivity did not increase significantly. Incubation of erythrocytes obtained during hypoventilation with antidigoxin antibody restored the Na+, K+ -ATPase activity (3.99 +/- 0.34 mmol Pi/mL-1/h-1). Cessation of hypoventilation was associated with decreases in diastolic blood pressure (70.5 +/- 2.2 mm Hg) and restoration of Na+, K+ -ATPase activity in erythrocytes (2.99 +/- 0.43 mmol Pi/mL-1/h1).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of two endogenous Na+,K(+)-ATPase inhibitors, marinobufagenin and ouabain, on isolated rat aorta

Previously, we reported that the venom of Bufo marinus toad contains a Na+,K(+)-ATPase inhibitor with potent vasoconstrictor activity. In the present study, using thin-layer chromatography in Silicagel 60 F254 + 366, we separated a vasoactive substance from a mixture of steroids from Bufo marinus venom. Based on chromatographic mobility of this substance and typical color reaction after its vizualization with SbCl3, we identified it as a previously described steroid, marinobufagenin. Vasoconstrictor and Na+,K+ pump inhibitory properties of marinobufagenin were studied in isolated rat aortic rings and compared with those of ouabain. Ouabain (10-100 mumol.1-1) produced weak vasoconstriction, which was blocked by 2 mumol.1-1 phentolamine. 10 mumol.1-1 ouabain stimulated, and at higher concentrations inhibited, the Na+,K+ pump. 2 mumol.1-1 phentolamine abolished the activating effect of 10 mumol.1-1 ouabain on the Na+,K+ pump, but did not alter the inhibitory action of higher concentrations of ouabain. By contrast, marunibufagenin elicited rapid and strong vasoconstriction and inhibited ouabain-sensitive 86Rb uptake. Antidigoxin antibody antagonized the vasoconstrictor responses to marinobufagenin, but not to ouabain. 2 mumol.1-1 phentolamine did not alter the constrictor effect of marinobufagenin. In solid-phase digoxin immunoassay, marinobufagenin demonstrated higher digoxin-like immunoreactivity than ouabain.