Human Cardiac Muscle Research Articles

Immunohistochemical localization of xanthine oxidase in human cardiac and skeletal muscle

The generation of a monoclonal antibody specific to xanthine oxidase and its use in the distribution of the enzyme in human tissue is described. Xanthine oxidase was purified from human and bovine milk by a rapid method, allowing for minimal proteolytic degradation, and the purified enzyme preparations were used for the immunization of BALB/c mice as well as for the subsequent selection of hybridomas. The hybridoma clone X1-7, IgG (2a, kappa-light chain) was selected for further analysis and demonstrated to precipitate xanthine oxidase from human liver and skeletal muscle extracts. As determined by SDS-polyacrylamide gel electrophoresis of eluates from affinity chromatography, the X1-7 antibody bound to a main protein of 155 kDa, from human milk and skeletal muscle, and to proteins of 155, 143 and 95 kDa from human liver. Immunohistochemical studies, using two of the monoclonal antibodies with differing epitope specificity, revealed xanthine oxidase to be localized mainly in the vascular smooth muscle cells but also in a proportion of endothelial cells of capillaries and smaller vessels in both human cardiac and skeletal muscle. Immunoreactivity was additionally observed in human macrophages and mast cells. The results of the present study confirm previous reports of the presence of xanthine oxidase in capillary endothelial cells, but also demonstrates additional localization of the enzyme in vascular smooth muscle cells, macrophages and mast cells. The current findings verify that the distribution of xanthine oxidase in human tissue includes cardiac and skeletal muscle.

Chromosome Mapping of Five Human Cardiac and Skeletal Muscle Sarcoplasmic Reticulum Protein Genes

Fluorescence in situ hybridization (FISH) experiments were performed using genomic and complementary DNA probes in order to determine the location on human chromosomes for five genes expressed in cardiac and skeletal muscle sarcoplasmic reticulum. The chromosome location of each gene was determined in terms of both cytogenetic bands and fractional chromosome length. The ATP2A2 gene, expressing the SERCA2 isoform of the Ca2+ pump, maps to bands 12q23-q24.1, the phospholamban gene (PLN) to 6q22.1, the human skeletal muscle calsequestrin gene (CASQ1) to band 1q21, the cardiac calsequestrin gene (CASQ2) to bands 1p11-p13.3, and the cardiac calcium release channel gene (RYR2) to the interval between band 1q42.1 (distal) and band 1q43 (proximal).

Isolation and characterization of a Streptococcus pyogenes protein that binds to basal laminae of human cardiac muscle

A 9-kDa glycosaminoglycan-binding protein (GAG-BP) was isolated from Streptococcus pyogenes and purified to homogeneity by affinity chromatography on heparin-agarose. The protein selectively bound to the basal laminae of human cardiac muscle and had an apparent dissociation constant of 2.5 x 10(-7) M. Chemical analyses indicated that the GAG-BP was rich in alanine, lysine, and arginine (pI 9.5) and devoid of tyrosine, methionine, histidine, and half-cystine. There were no detectable carbohydrate or phosphate substituents. The amino acid sequence of the N terminus of GAG-BP showed homology with those of histone-like DNA-binding proteins of several other bacteria. Circular dichroism spectroscopy indicated that the protein was made up of 50% beta-sheet and 50% beta-turn and random coil in aqueous solution; however, when the protein complexed with heparin, it adopted a more ordered structure containing 25% alpha-helix, 50% beta-sheet, and 25% beta-turn and random coil. The GAG-BP cross-reacted serologically with a component of similar size in extracts of other group A streptococci and was present in the culture medium during late logarithmic growth.

Effect of calcium binding protein modulators on myofibrillar MgATPase activity and cGMP‐inhibitable phosphodiesterase activity from human cardiac muscle

AbstractCardiac muscle force development and shortening result from the interaction between actin and myosin within the myofibrillar contractile unit. This interaction is dependent upon intracellular Ca2+ and is controlled by the troponin‐tropomyosin regulatory proteins situated along the length of the actin thin filament. Enhancing the Ca2+ sensitivity of cardiac contractile protein interactions has been proposed as a novel mechanism for some positive inotropic agents. These myofibrillar Ca2+ sensitizers have variable effects on myofibrillar MgATPase activity among nonhuman animal species, and different effects between myofibrils from failed nonhuman hearts are evident. In this study, we have evaluated several myofibrillar calcium sensitizers, at maximal testable concentrations, for their effects on the calcium‐activated MgATPase of myofibrils prepared from normal human hearts and from hearts of patients with congestive heart failure. Bepridil (100 μM) increased MgATPase at pCA 9.0 (basal activity) and pCa 6.5 (an intermediate concentration of Ca2+ which stimulated activity 42–56% of maximal), with no effect at pCa 5.0 (maximal Ca2+ activity) in both normal and failing hearts. APP 201–533 (300 μM) increased MgATPase at pCa 6.5 in all hearts, but increased MgATPase at pCa 5.0 only in normal hearts. Pimobendan (100 μM) increased MgATPase at pCa 6.5 only in normal hearts and increased activity at pCa 5.0 only in failing hearts. In contrast, trifluoperazine (100 μM) reduced MgATPase at pCa 5.0 and pCa 9.0 in all hearts and at pCa 6.5 in failing hearts. The stimulating effects of bepridil, APP 201–533, and pimobendan (approximately 7–17%) were less than those observed in studies with nonhuman cardiac myofibrils (typically 30–40%). These data suggest that some myofibrillar Ca2+ sensitizers can have either modest stimulatory or inhibitory activity on human cardiac myofibrillar MgATPase activity. While these (Ca+‐sensitizing) effects on MgATPase activity are statistically significant, the biological relevance with respect to enhancing cardiac contractility is equivocal. Furthermore, both pimobendan and APP 201–533 inhibited cAMP‐phosphodiesterase III purified from failing human hearts with IC50 values of 0.35 and 2.0 μM, respectively. Since other inotropic mechanisms, such as cAMP‐phosphodiesterase inhibition, are also evident at much lower concentrations with some of these agents, the relevance of myofibrillar Ca2+ sensitization as the predominant inotropic mechanism of action of these compounds is questionable. © 1993 Wiley‐Liss, Inc.

Positive inotropic effect in the heart produced by acetylcholine.

The effect of acetylcholine on cardiac muscle contractility and hemodynamics was investigated in human atrial strips and in isolated working rat heart. Activation of the muscarinic receptor in the heart muscle is generally known to result in negative chronotropic and inotropic effects. In our study, positive inotropic effects of acetylcholine (ACh) were observed in both human right atrial strips and in the working rat heart. Exposure of the human right atrial strips to ACh (10(-7)-10(-4) M) produced a dose dependent tri-phasic (positive-negative-positive) inotropic effect in approximately 40% of the strips. In muscle strips that exhibited only a negative inotropic effect, a positive response was observed following washout of ACh. Both positive and negative effects were antagonized by atropine. Exposure of the paced working rat heart to ACh (10(-7) - 10(-5) M) resulted in a dose dependent decrease in mean coronary flow followed by depression in cardiac function. When the heart was initially treated with the vasodilator adenosine (2 x 10(-6) M), exposure to ACh (10(-7) - 10(-5) M) had no effect on coronary flow and produced a dose dependent augmentation of all cardiodynamic indices: left ventricular pressure, isovolumic pressure, cardiac output, maximal aortic flow and stroke work. This positive response was antagonized by atropine. Exposure of the rat ventricular strips increased the formation of [3H]phosphoinositide breakdown products (e.g. inositol phosphates IP, IP2, IP3). These observations demonstrate that cholinergic muscarinic stimulation may produce positive inotropic effects in both human and rat cardiac muscle. Furthermore, our results suggest that IP3 may be a mediator in this process.

Relationship between inotropic activity and phosphodiesterase inhibition for flosequinan and milrinone

The goal of this study was to assess the relationship between the positive inotropic response to high concentrations of the vasodilators flosequinan and BTS 53 554 (the sulfone metabolite of flosequinan) and the effect of both compounds on different forms of cyclic nucleotide phosphodiesterase. In addition, the relationship between inotropic activity and phosphodiesterase inhibition for the cardiotonic milrinone was also evaluated. All three agents exerted a positive inotropic effect on human cardiac muscle fibers. The concentration of milrinone required to increase cardiac contractility was comparable to the concentration required to inhibit the milrinone-sensitive subclass of cyclic AMP-specific phosphodiesterase (type III phosphodiesterase). However, no such relationship was observed for flosequinan and BTS 53 554. These results suggest that the cardiac response to high concentrations of flosequinan and BTS 53 554 is not mediated by inhibition of type III phosphodiesterase.

Molecular characterization of the gene encoding the gamma subunit of the human skeletal muscle 1,4-dihydropyridine-sensitive Ca2+ channel (CACNLG), cDNA sequence, gene structure, and chromosomal location

cDNA clones of the gamma subunit of the skeletal muscle 1,4-dihydropyridine-sensitive voltage-dependent Ca2+ channel were isolated from a human fetal skeletal muscle cDNA library using the rabbit gamma cDNA as a probe. The DNA sequence of the entire human cDNA was determined. Cosmids that contained the human gamma gene were isolated and used to determine the genomic organization of the coding sequences. Four exons were identified, spanning 12.5 kilobases of DNA. Reverse-transcribed polymerase chain reaction analysis detected the gamma transcript in human and mouse skeletal muscle RNAs, but not in RNA from human brain or cardiac muscle or from mouse brain, cardiac muscle, spleen, kidney, liver, or stomach. A polymorphic dinucleotide repeat within the gamma gene was identified. This repeat was used to type a subset of the Centre d'Etude du Polymorphisme Humain families. Linkage analysis indicates that the gamma gene is tightly linked (Z = 12.94, theta = 0.001) to growth hormone at chromosome 17q23, a region that also contains the adult skeletal muscle Na+ channel.

Measurement of T1 relaxation times of cardiac phosphate metabolites using BIR-4 adiabatic RF pulses and a variable nutation method.

T1 relaxation times of PCr and beta-ATP in human cardiac and skeletal muscle were evaluated using a variable nutation method. This allows T1 measurements with a constant TR and a significant reduction in acquisition time compared with the partial saturation method. Four 1D CSI datasets were obtained using 30 degrees, 45 degrees, 60 degrees, and 90 degrees BIR-4 adiabatic RF pulses within 40 min. The T1 of the phosphate phantom obtained with this method agreed with values obtained with the partial saturation method. The T1s of PCr and beta-ATP in heart are 3.98 +/- 0.18 s and 1.86 +/- 0.16 s (mean +/- SE). Our results demonstrated that T1 values in heart and skeletal muscle are not significantly different.

Human cardiac muscle magnesium and potassium concentrations: can skeletal muscle, mononuclear blood cells, erythrocyte and plasma concentrations provide a surrogate measure?

Human cardiac muscle magnesium and potassium concentrations: can skeletal muscle, mononuclear blood cells, erythrocyte and plasma concentrations provide a surrogate measure?

Organization of non-muscle myosin during early murine embryonic differentiation

Abstract A monoclonal antibody (3D10) recognizing myosin heavy chain was isolated following immunization with a synthetic peptide sequence of eight amino acids. The antibody reacted with purified rabbit skeletal myosin and light mero-myosin in enzyme-linked immunosorbent assays and Western immunoblotting. A band of approximately 200 kDa was detected in cell extracts of an embryonal carcinoma (EC) cell line (P19EC) and one of its cloned differentiated derivatives, suggesting reactivity against non-muscle myosin. By indirect immunofluorescence, typical myosin banding patterns were observed in cryostat sections of human skeletal and cardiac muscle tissue. In undifferentiated P19EC cells, speckled immunofluorescent staining was observed in the cytoplasm that became organized in cortical rings where the cells made direct contact with each other. These rings consisted of circular bundles of F-actin decorated by myosin. Undifferentiated embryonic stem (ES) cells derived directly from mouse embryos shared the same features, although the pattern was less pronounced. Human testicular primary germ cell tumours showed cortical staining in the embryonal carcinoma component reminiscent of the staining of EC cells in vitro while cytoplasmic staining was observed in tumour cells with a differentiated morphology. In preimplantation embryos, the immunofluorescent staining was observed at cell apices of blastomeres of morula stage embryos. In blastocysts, staining of inner cell mass cells was not detectable. By contrast, various differentiated derivatives of P19EC contained extensive F-actin microfilament bundles throughout the cytoplasm decorated with myosin. Thick stress fibers in filopodious extensions of cells were particularly highly decorated by myosin. Over the nucleus, linear arrays of myosin containing speckled patterns of immunofluorescence were observed that were not associated with F-actin. The same pattern of staining could be observed in trophectoderm cells of the blastocyst. We conclude that embryonic non-muscle myosin is organized in specific patterns depending on the state of differentiation. As the myosin is primarily associated with F-actin we suspect that it forms part of a contractile apparatus that may have significance during embryonic development.

Effects of subcultivation and culture medium on differentiation of human fetal cardiac myocytes.

Previous work has suggested that subcultivated human fetal heart muscle cell cultures contain immature cardiac muscle cells capable only of limited differentiation after mitogen withdrawal. We studied several human fetal heart cultures (14-15 wk gestation) at several passage levels using immunocytochemistry, autoradiography, and Northern blot analysis. Characteristics in high-mitogen (growth) medium were compared with those after serum withdrawal. Cultured cells from one heart, expanded through 2 passages in growth medium, did not beat; however, 75% of cells did beat after subsequent culture for 24 days in low-serum (differentiation) medium containing insulin. In confluent cultures after 1 passage, there was no detectable difference in the number of cardiac myocytes present in growth medium compared with that 7 days after serum withdrawal. After 4 passages, however, serum withdrawal increased the number of cells expressing immunoreactive sarcomeric myosin heavy chain by 100-fold; expression of immunoreactive sarcomeric actin and alpha-cardiac actin mRNA also increased in the same cultures. Similar results were obtained in cultures kept in differentiation medium for 20 days before passage and expansion in growth medium. Using isopycnic centrifugation, a high-density cell fraction was isolated which contained no immunostained myocytes in growth medium but numerous myocytes after serum withdrawal. Combined immunocytochemistry/autoradiography showed that myocytes synthesize DNA in growth medium and in serum-free medium containing fibroblast growth factor, but not in serum-free medium alone. The results indicate that a) human fetal cardiac muscle cells proliferate in vitro and can maintain a phenotype characteristic of fetal myocytes after multiple subcultivations followed by serum withdrawal; b) after subcultivation in growth medium, some myocytes modulate their phenotype into one in which detectable levels of cardiac contractile proteins are expressed only after mitogen withdrawal, and c) the phenotype attained after serum withdrawal is in part dependent on passage level. Cultured human fetal myocardial cells may provide a useful experimental system for the study of human cardiac muscle cell biology.

Primary structure and functional expression of the human cardiac tetrodotoxin-insensitive voltage-dependent sodium channel.

The principal voltage-sensitive sodium channel from human heart has been cloned, sequenced, and functionally expressed. The cDNA, designated hH1, encodes a 2016-amino acid protein that is homologous to other members of the sodium channel multigene family and bears greater than 90% identity to the tetrodotoxin-insensitive sodium channel characteristic of rat heart and of immature and denervated rat skeletal muscle. Northern blot analysis demonstrates an approximately 9.0-kilobase transcript expressed in human atrial and ventricular cardiac muscle but not in adult skeletal muscle, brain, myometrium, liver, or spleen. When expressed in Xenopus oocytes, hH1 exhibits rapid activation and inactivation kinetics similar to native cardiac sodium channels. The single channel conductance of hH1 to sodium ions is about twice that of the homologous rat channel and hH1 is more resistant to block by tetrodotoxin (IC50 = 5.7 microM). hH1 is also resistant to mu-conotoxin but sensitive to block by therapeutic concentrations of lidocaine in a use-dependent manner.

Human cardiac and skeletal muscle spectrins: differential expression and localization.

We describe multiple human cardiac and skeletal muscle spectrin isoforms. Cardiac muscle expresses five erythroid alpha,beta spectrin-reactive isoforms with estimated MR's of 280, 274, 270, 255, and 246 kD, respectively. At least one nonerythroid alpha-spectrin of MR 284 kD is expressed in heart. While skeletal muscle shares the 280, 270, and 246 kD erythroid spectrins, it expresses an immunologically distinct 284 kD nonerythroid alpha-spectrin isoform. The 255 kD erythroid beta-spectrin isoform is specific for cardiac tissue. By immunocytochemistry, both erythroid beta- and nonerythroid alpha-spectrins are localized to costameres, the plasma membrane, and the neuromuscular junctional region.

Mechanism underlying the reduced positive inotropic effects of the phosphodiesterase III inhibitors pimobendan, adibendan and saterinone in failing as compared to nonfailing human cardiac muscle preparations

The present study was performed to compare the effects of the new positive inotropic phosphodiesterase III inhibitors pimobendan, adibendan, and saterinone on the isometric force of contraction in electrically driven ventricular trabeculae carneae isolated from explanted failing (end-stage myocardial failure) with those from nonfailing (prospective organ donors) human hearts. In preparations from nonfailing hearts the phosphodiesterase inhibitors, as well as the beta-adrenoceptor agonist isoprenaline, the cardiac glycoside dihydro-ouabain, and calcium, which were studied for comparison, revealed pronounced positive inotropic effects. The maximal effects of pimobendan, adibendan, and saterinone amounted to 56%, 36% and 45%, respectively, of the maximal effect of calcium. In contrast, in preparations from failing hearts the phosphodiesterase III inhibitors failed to significantly increase the force of contraction and the effect of isoprenaline was markedly reduced. The effects of dihydroouabain and calcium were almost unaltered. The diminished effects of isoprenaline were restored by the concomitant application of phosphodiesterase inhibitors. To elucidate the underlying mechanism of the lack of effect of the phosphodiesterase III inhibitors in the failing heart we also investigated the inhibitory effects of these compounds on the activities of the phosphodiesterase isoenzymes I-III separated by DEAE-cellulose chromatography from both kinds of myocardial tissue. Furthermore, the effects of pimobendan and isoprenaline on the content of cyclic adenosine monophosphate (determined by radioimmunoassays) of intact contracting trabeculae were studied. The lack of effect of the phosphodiesterase inhibitors in failing human hearts could not be explained by an altered phosphodiesterase inhibition, since the properties of the phosphodiesterase isoenzymes I-III and also the inhibitory effects of the phosphodiesterase inhibitors on these isoenzymes did not differ between failing and nonfailing human myocardial tissue. Instead, it may be due to a diminished formation of cyclic adenosine monophosphate in failing hearts, presumably caused mainly by a defect in receptor-adenylate cyclase coupling at least in idiopathic dilated cardiomyopathy. Both the basal and the pimobendan-stimulated or isoprenaline-stimulated contents of cyclic adenosine monophosphate of intact contracting trabeculae from failing hearts were decreased compared with the levels in nonfailing hearts. However, under the combined action of isoprenaline and pimobendan the cyclic adenosine monophosphate level reached values as high as with each compound alone in nonfailing preparations, and in addition the positive inotropic effect of isoprenaline was restored. These findings may have important clinical implications. Along with the elevated levels of circulating catecholamines the positive inotropic effects of the phosphodiesterase inhibitors may be maintained in patients with heart failure.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification ofα andβ subunits of phosphorylase‐b‐kinase in human liver and cardiac muscle by affinity chromatography and immunodetection

Journal of Inherited Metabolic DiseaseVolume 14, Issue 3 p. 308-310 Short Communication Purification ofα andβ subunits of phosphorylase-b-kinase in human liver and cardiac muscle by affinity chromatography and immunodetection T. Podskarbi, T. Podskarbi Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this authorW. Endres, W. Endres Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this authorY. S. Shin, Y. S. Shin Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this author T. Podskarbi, T. Podskarbi Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this authorW. Endres, W. Endres Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this authorY. S. Shin, Y. S. Shin Children's Hospital, University of Munich, Lindwurmstrasse 4, München 2, 8000 GermanySearch for more papers by this author First published: 01 May 1991 https://doi.org/10.1007/BF01811689Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume14, Issue3May 1991Pages 308-310 RelatedInformation

Effects of intravenous glutamate on substrate availability and utilization across the human heart and leg

To study the effect of monosodium glutamate on hemodynamics and on substrate metabolism in cardiac and skeletal muscle, an intravenous (IV) dose of 1.2, 2.5, or 5.0 mg/kg body weight was administered to 27 patients during arterial-coronary sinus catheterization (15 patients) or arterial-femoral vein catheterization (13 patients). Data were obtained for 25 minutes after the injection. Arterial glutamate concentrations increased 2.5–5 fold in a dose-related manner. Glutamate administration reduced arterial levels of free fatty acids by 25% ( P < .001), of lactate by 13% ( P < .05), and of alanine by 6% ( P < .05). Arterial glucose increased by 10% ( P < .001) and arterial insulin was increased threefold ( P < .01). Myocardial uptake of free fatty acids decreased by 25% ( P < .001), whereas uptakes of glutamate and glucose increased by 60% ( P < .001) and 100% ( P < .001), respectively. Cardiac release of citrate increased transiently ( P < .05), whereas consumption of lactate and releases of alanine were unchanged by the glutamate. Across the leg, the arteriovenous differences of glutamate were elevated threefold to eightfold (dose-related) ( P < .001), and that of glucose was doubled ( P < .01). The release of citrate increased ( P < .01). Arterial-femoral vein gradients of free fatty acids, lactate, and alanine remained unchanged. Heart rate, blood pressure, coronary sinus flow, coronary vascular resistance, and cardiac oxygen uptake were unmodified by glutamate. Six patients complained of short-lasting burning sensations after the highest glutamate doses. In conclusion, glutamate administration stimulates insulin secretion and changes substrate availability and utilization in human cardiac and skeletal muscle from free fatty acids toward glucose and glutamate.

Muscle and species reactivity of mouse monoclonal antibodies to human eye muscle membrane antigens

We studied the tissue and species reactivity of mouse monoclonal antibodies (MCAB) produced by immunizing mice with a 100,000g ultracentrifuged preparation of human eye muscle (HEM) membranes. Twenty-three MCABs, 20 of which reacted in an enzymelinked immunosorbent assay (ELISA) with HEM membrane, 2 with human thyroid membrane, and 1 nonreactive negative control, were selected for the study. The muscle and species specificity of 6 of the most reactive and more restrictively reactive MCAB were studied in more detail. All reacted in ELISA with human skeletal muscle membrane and, to a lesser extent, with human cardiac muscle membrane, but not with human brain membrane. The 6 MCAB cross-reacted with eye muscle membrane prepared from pig but not rat, although reactivity with human tissue was greatest for all MCAB tested. When tested in immunoblotting with HEM and thyroid membranes, 3 of 6 MCAB reacted with a 64-kDa protein in HEM, 2 of which also reacted with an antigen of the same molecular weight in thyroid membrane. In a complement-mediated antibody-dependent cytotoxicity assay, 5 of 19 MCAB lysed HEM cells, 6 of 21 lysed human skeletal muscle cells, and 10 of 22 lysed human thyroid cells. These findings support results from earlier clinical studies which showed that eye muscle membrane reactive autoantibodies in the serum of patients with thyroid-associated ophthalmopathy cross-react with membrane prepared from other striated muscle. The significance of eye muscle, skeletal muscle, and thyroid cross-reactivity of MCAB is discussed in the context of autoimmune thyroid disease and ophthalmopathy.

Differential expression of multiple spectrin isoforms in human cardiac and skeletal muscle

Differential expression of multiple spectrin isoforms in human cardiac and skeletal muscle

Human malic enzymes in heart and muscle: Evidence of a selective distribution

The NADP(+)-dependent activity of malic enzymes EC 1.1.1.39 and EC 1.1.1.40 was studied in human cardiac and skeletal muscle obtained from living subjects. We used polyacrylamide gel electrophoresis to detect and extract the enzymatic forms and starch gel electrophoresis to confirm their identification. This simple procedure allowed us to provide evidence of a selective NADP(+)-dependent distribution of malic enzyme activities between the two muscular tissues, using a smaller amount of sample than used with previous methods.

Inotropic effects of angiotensin II on human cardiac muscle in vitro.

The direct effects of angiotensin II (Ang II) on human cardiac muscle were investigated using isolated trabecular muscles from failing and functionally normal hearts. Atrial and ventricular trabeculae were studied. Results demonstrated a positive inotropic effect of Ang II on human cardiac muscle. Comparison of the effects of Ang II among groups indicated that the responsiveness tended to be greater in atrial and normal muscle compared with failing muscle. Results of this study also demonstrated heterogeneity in the responsiveness to Ang II among human muscles, which was not correlated with patient age, sex, diagnosis, prior treatment with angiotensin converting enzyme inhibitor, or heart function. A significant correlation between response to Ang II and response to isoproterenol was demonstrated in failing ventricular trabeculae, which may suggest that defects in beta-adrenergic responsiveness in the failing human ventricle are accompanied by a loss of responsiveness to Ang II. Studies were extended to the Syrian cardiomyopathic hamster and its control. A dose-dependent inotropic response occurred in normal hamster ventricular muscle but was significantly diminished in cardiomyopathic muscle. Ang II did not shorten the timing of contraction, and pretreatment with adrenergic-blocking agents did not shift the dose-response curve, indicating that the response was not cyclic AMP mediated. This study demonstrates for the first time that Ang II can exert an inotropic effect directly on human cardiac muscle and confirms that there is a direct effect of Ang II on hamster cardiac muscle. The study further suggests, however, that the inotropic response to Ang II in cardiac muscle is heterogeneous and may be diminished by heart failure.