The endogenous inhibitor of NCX1 does not resemble the properties of digitalis compound

In our previous study, we ware successful in isolation and purification of an endogenous inhibitor of the Na/Ca exchanger (NCX1) from the calf ventricle extracts. The purified factor has characterized to have strong positive inotropic effect on isometric contractions of isolated ventricle strips of guinea pig. A possibility is that besides the NCX1 the endogenous factor may also interact with other ion-transport systems (e.g., Na,K-ATPase) involved in modulation of muscle contractility-relaxation. Therefore, a primary goal of the present study was to detect a possible effect of newly found NCX1 inhibitor on Na,K-ATPase and Ca-ATPase activities. The preparations of isolated sarcolemma vesicles were used for this goal. Although the crude extracts of calf ventricles can inhibit both the Na/Ca exchange and Na,K-ATPase, these two inhibitory activities can be separated on the Sephadex G-10 column, meaning that different molecular entities might be responsible for inhibition of Na/Ca exchange and Na,K-ATPase. Addition of 100 U of purified endogenous factor to the assay medium results in nearly complete inhibition of forward (Na(i)-dependent Ca-uptake) and reverse (Na(o)-dependent Ca-efflux) modes of Na/Ca exchange. On the other hand, no effect was detected on activities of Na,K-ATPase and Ca-ATPase even in the presence of 500 U of purified factor in the assay medium. In light of the present data, it is concluded that the endogenous inhibitor of NCX1 does not resemble the targeting properties of digitalis like compound. Obviously, more systematic studies are required in the future for resolving a possible interaction of the endogenous inhibitor of NCX1 with other ion-transport systems involved in calcium homeostasis and action potential.     

Direct Loading of the purified endogenous inhibitor into the cytoplasm of patched cardiomyocytes blocks the ion currents and calcium transport through the NCX1 protein

The Na(+)-Ca(2+) exchanger in mammalian heart muscle (NCX1) is the central transporter protein that regulates extrusion of Ca(2+) from the heart cell. However, the functional biochemistry and physiology of NCX1 have been severely hampered by the absence of any specific high-affinity inhibitor. Here we describe advanced procedures for purifying a candidate inhibitor, previously called endogenous inhibitor factor (NCX(IF)), and demonstrate its direct actions on NCX1 activities in the single-cell system. A combination of advanced HILIC (hydrophilic interaction liquid chromatography) procedures with analytical tests suggests that the properties of NCX(IF) resemble those of a small (disaccharide size) polar molecule lacking any aromatic rings, conjugated bonds, or a primary amino group. The effects of NCX(IF) on the NCX1-mediated ion currents (I(NCX)) and cytosolic Ca(2+) extrusion were detected by a combination of patch-clamp and confocal microscopy under conditions in which the purified NCX(IF) was directly loaded into the cytoplasm of patched cardiomyocytes. It was demonstrated that cytosolic NCX(IF) blocks the Ca(2+)-activated NCX1 inward current and the accompanying extrusion of Ca(2+) from the cell with high efficacy. A constant fraction of NCX1 inhibition was observed under conditions in which the cytosolic [Ca(2+)](i) was varied at fixed doses of NCX(IF), suggesting that the degree of inhibition is controlled by NCX(IF) dose and not by cytosolic Ca(2+) concentration. NCX(IF) blocks equally well both the Ca(2+) extrusion and Ca(2+) entry modes of NCX1, consistent with thermodynamic principles expected for the functioning of a bidirectional "carrier-type" transport system. We concluded that NCX(IF) interacts with a putative regulatory domain from the cytosolic side and, thus, may play an important regulatory role in controlling Ca(2+) signaling in the heart. This may represent a new potential tool for developing novel treatments for cardiac Ca(2+) signaling dysfunction.     

The low molecular weight inhibitor of NCX1 interacts with a cytosolic domain that differs from the ion-transport site of the Na/Ca exchanger

The endogenous inhibitory factor (NCX(IF)) of the cardiac Na/Ca exchanger (NCX1) is a low molecular weight substance, which has a strong capacity to modulate the ventricle muscle contractility. Previously, we have shown that NCX(IF) can completely inhibit either the forward (Na(i)-dependent Ca-uptake) or reverse (Na(o)-dependent Ca-release) mode of Na/Ca exchange as well as its partial reaction, the Ca/Ca exchange. Although the preliminary studies have shown that NCX(IF) can rapidly (within few milliseconds) interact with a putative inhibitory site of the Na/Ca exchanger protein (or within its vicinity), it was not clear whether the NCX(IF) can directly interact with the ion transport sites of the exchanger protein or the interaction site of NCX(IF) is distinct from the ion-binding/transport site of NCX1. In order to segregate between these possibilities the NCX(IF) was tested for its capacity to compete with Ca at the cytosolic side by using the preparation of sarcolemma vesicles having predominantly the inside-out orientation. For this goal, the initial rates of Na(i)-dependent (45)Ca-uptake were measured in the presence of extravesicular (cytosolic) NCX(IF) under conditions in which the concentration of extravesicular Ca was varied (2-200 microM) and intravesicular Na was kept fixed at saturating concentration (160 mM). Under these conditions the NCX(IF) results in several fold decrease in V(max) values, while having no significant effect on the K(m). Taking into account the molecular weight of 350-550 Da (derived from the gel-filtration and mass-spectra data), the experimentally measured inhibitory potency of NCX(IF) can be estimated as the IC(50) = 0.3-0.6 microM. Therefore, it is concluded that the NCX(IF) is reasonably potent blocker, which interacts with cytosolic domain thereby preventing the ion-translocation (and not ion-binding) events.     

Purified endogenous inhibitor of the Na/Ca exchanger can enhance the cardiomyocytes contractility and calcium transients

Previous studies have shown that the newly found endogenous inhibitor (NCX(IF)) of the cardiac Na/Ca exchanger (NCX1) is capable of regulating the muscle strip's contractility and relaxation. Here, the effects of purified NCX(IF) were tested on single cell shortening-lengthening (by using the IR CCD camera coupled with the two-edge video-detector) and [Ca]i-transients (by monitoring the changes in fluo-3 fluorescence). A perfusion of isolated cardiomyocytes (paced at 0.5-1.0 Hz) with NCX(IF) results in 4-6-fold enhancement in the amplitude of cell shortening-lengthening reaching the steady-state levels within 5-8 min (n=20, p<0.009). Simultaneous recordings of cell shortening-lengthening and [Ca]i-transients from the same cell show that the amplitude enhancement is associated with accelerated decay of both signals. Therefore, the NCX(IF)-dependent modulation of the single cell contractility is primarily governed by Ca-related mechanisms. The observed data are consistent with a proposal suggesting that the inhibition of NCX1 by NCX(IF) results in Ca-dependent activation of SERCA (SR Ca ATPase), yielding the accelerated decay of the [Ca]i-transients. The subsequent increase in the SR Ca content may result in enhanced Ca-release reflecting the manifested promotion of [Ca]i-transients. More systematic study is required for confirming this working hypothesis.     

Quantitative analysis of Na+-Ca2+ exchanger expression in guinea-pig heart.

In previous studies, regional variations in the expression of the Na+-Ca2+ exchanger (NCX) have been examined qualitatively in human heart using the C2C12 monoclonal antibody [Wang, J., Schwinger, R.H., Frank, K., Muller-Ehmsen, J., Martin-Vasallo, P., Pressley, T.A., Xiang, A., Erdmann, E. & McDonough, A.A. (1996) J. Clin. Invest. 98, 1650-1658]. Although NCX expression was found to be significantly lower in the atria compared to the septum, no significant differences were found between atrial and ventricular tissue. NCX has been located in the general sarcolemma and t-tubules of ventricular muscle and as t-tubules are sparse in atrial tissue compared to ventricular tissue, it is surprising that NCX expression was found to be similar in both atria and ventricles [Wang et al. (1996)]. To reinvestigate this, we have used SDS/PAGE and a quantitative Western blotting technique to determine the pattern of expression of NCX in guinea-pig heart in tissue samples from left atrium, right atrium, septum, left ventricle and right ventricle. NCX protein expression was 17.5 +/- 3.9 pmol.mg-1 of protein in the left atrium and 29.2 +/- 6.1 pmol.mg-1 of protein in the right atrium, which were both significantly lower (P < 0.05) than NCX expression in the septum, left ventricle and right ventricle (64.7 +/- 15.2, 76.8 +/- 19.5 and 69.4 +/- 14.1 pmol.mg-1 of protein, respectively, n = 7). These differences in NCX expression may reflect variations in the cellular location of NCX protein in these regions. To study this, we used confocal immunofluorescence of single isolated myocytes to examine differences in the proportion of fluorescent staining on the general surface membrane compared with the interior of the cell (which presumably reflects a t-tubular location). We found that the general membrane staining was 79.0 +/- 1.2% in cells from the atria which was significantly higher (P < 0. 001) than that seen in cells from the septum, left ventricle and right ventricle, with 48.1 +/- 1.1%, 48.2 +/- 1.8% and 45.6 +/- 1.3%, respectively (n = 20). These results illustrate a similar pattern of NCX expression in guinea-pig and human, with expression in atrial tissue significantly lower than in ventricular tissue. However, the cellular location of NCX differs regionally; in atrial tissue, the majority of the NCX protein is located in the general sarcolemma whereas in ventricular and septal tissue, approximately 50% of NCX protein is located within the cell (presumably at the level of the t-tubules).     

Analysis of the adenovirus type 5 proteome by liquid chromatography and tandem mass spectrometry methods

We compared detection sensitivity and protein sequence coverage of the adenovirus type 5 proteome achievable by liquid chromatography and tandem mass spectroscopy (LC/MS/MS) using three sample preparation and clean up methods. Tryptic digestion was performed on either purified viral proteins or whole virus, and followed by shotgun sequencing using tandem mass spectrometry for peptide identification. We used a recombinant adenovirus type 5 as a test system. The methods included separation of adenoviral proteins by reversed-phase high-performance liquid chromatography followed by tryptic digestion and analysis by LC/MS/MS. Alternatively, the purified whole virus was digested with trypsin and the peptides separated either by one-dimensional (reversed-phase) or by two-dimensional (cation exchange and reversed-phase) chromatography and analyzed by tandem mass spectrometry. A total of 11 protein species were identified from 154 peptides. All of the major viral proteins were found. In addition, two minor proteins, the 23 kDa viral protease and the late L1 protein, were identified for the first time by chromatography based assays. The 23 kDa viral protease, present at only 10 copies per virus, and representing 0.2% of the protein content of the virus, was detected by the 2D LC/MS/MS analysis of the whole virus digest from a sample containing only 70 fmols of the protein. This demonstrates the high sensitivity and selectivity of the method. The 2D LC/MS/MS analysis of the whole virus digest was also able to detect all viral proteins with copy numbers at or above 10/virus particle, with broad coverage of the amino acid sequences. Coverage ranged from 2 to 54%, a majority between 20 and 35%, suggesting the possibility of using this analysis to assess the purity of the virus preparations. This broad coverage may also provide a useful approach to identify posttranslational modifications on the structural proteins of the adenovirus.     

Intermediate filaments in smooth muscle

The intermediate filament (IF) network is one of the three cytoskeletal systems in smooth muscle. The type III IF proteins vimentin and desmin are major constituents of the network in smooth muscle cells and tissues. Lack of vimentin or desmin impairs contractile ability of various smooth muscle preparations, implying their important role for smooth muscle force development. The IF framework has long been viewed as a fixed cytostructure that solely provides mechanical integrity for the cell. However, recent studies suggest that the IF cytoskeleton is dynamic in mammalian cells in response to various external stimulation. In this review, the structure and biological properties of IF proteins in smooth muscle are summarized. The role of IF proteins in the modulation of smooth muscle force development and redistribution/translocation of signaling partners (such as p130 Crk-associated substrate, CAS) is depicted. This review also summarizes our latest understanding on how the IF network may be regulated in smooth muscle. cytoskeleton; force development; vimentin; desmin     

The participation of the Na+-Ca2+ exchanger in primary cardiac myofibroblast migration, contraction, and proliferation

Cardiac ventricular myofibroblast motility, proliferation, and contraction contribute to post-myocardial infarct wound healing, infarct scar formation, and remodeling of the ventricle remote to the site of infarction. The Na+-Ca2+ exchanger (NCX1) is involved in altered calcium handling in cardiac myocytes during cardiac remodeling associated with heart failure, however, its role in cardiac myofibroblast cell function is unexplored. In this study we investigated the involvement of NCX1 as well as the role of non-selective-cation channels (NSCC) in cardiac myofibroblast cell function in vitro. Immunofluorescence and Western blots revealed that P1 cells upregulate alpha-smooth muscle actin (alphaSMA) and embryonic smooth muscle myosin heavy chain (SMemb) expression. NCX1 mRNA and proteins as well as Ca(v)1.2a protein are also expressed in P1 myofibroblasts. Myofibroblast motility in the presence of 50 ng/ml PDGF-BB was blocked with AG1296. Myofibroblast motility, contraction, and proliferation were sensitive to KB-R7943, a specific NCX1 reverse-mode inhibitor. In contrast, only proliferation and contraction, but not motility were sensitive to nifedipine, while gadolinium (NSCC blocker) was only associated with decreased motility. ML-7 treatment was associated with inhibition of the chemotactic response and contraction. Thus cardiac myofibroblast chemotaxis, contraction, and proliferation were sensitive to different pharmacologic treatments suggesting that regulation of transplasmalemmal calcium movements may be important in growth factor receptor-mediated processes. NCX1 may represent an important moiety in suppression of myofibroblast functions.     

TRPC3 channels colocalize with Na+/Ca2+ exchanger and Na+ pump in axial component of transverse-axial tubular system of rat ventricle

Transient receptor potential canonical (TRPC) proteins form Ca(2+)-permeable, nonselective cation channels activated after stimulation of G protein-coupled membrane receptors linked to phospholipase C (PLC). Although the PLC/inositol phosphate signaling pathway is known to exist in heart, expression and subcellular distribution of TRPC channel proteins in ventricular myocardium have not been evaluated. Of the six members of the TRPC channel family examined here, only TRPC3 was found by Western blot analysis of membrane proteins from rodent or canine ventricle. Likewise, only TRPC3 was observed in immunofluorescence analysis of thin sections from rat ventricle. TRPC3 was also the only family member observed in neonatal rat ventricular myocytes in culture. In longitudinal sections of rat ventricle, TRPC3 was predominantly localized to the intercalated disk region of the myocyte. However, transverse sections through heart muscle or single isolated adult myocytes revealed TRPC3-specific labeling in a vast network of intracellular membranes, where it colocalized with the Na(+)-K(+)-ATPase (NKA) pump and the Na(+)/Ca(2+) exchanger (NCX) but not with the ryanodine receptor or the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pump. Reciprocal immunoprecipitation assays from rat or canine ventricle showed that TRPC3 associates with NKA and NCX but not with the plasmalemmal Ca(2+)-ATPase pump. Immunoprecipitations from Sf9 insect cells heterologously expressing TRPC3, NKA, and NCX in various combinations revealed that NKA and NCX interact and that TRPC3 and NCX interact, but that TRPC3 does not directly associate with NKA. Together, these results suggest that TRPC3 is localized in the ventricular myocyte to the axial component of the transverse-axial tubular system, where it exists in a signaling complex that includes NCX and NKA.     

Effect of 6-hydroxydopamine on the gene expression of Na+/Ca2+ exchanger in the rat heart

The Na+/Ca2+ exchanger (NCX) is an important component of the process of excitation-contraction coupling in the heart muscle. The level of gene expression as well as transport activities of this membrane structure is changed under pathological conditions like ischemic injury, myocardial infarction or diabetes. In this work we focused on the question whether the adrenergic modulation affects gene expression of the NCX in rat hearts. NCX mRNA levels were studied in the left cardiac atrium (divided into ganglionic and nonganglionic part) and also in the left ventricle of rats treated with 6-hydroxydopamine (6-OHDA) in control and stressed conditions. We have shown that administration of 6-OHDA decreases mRNA levels of NCX in both ganglionic and nonganglionic part of the left atrium and also in the left ventricle. This effect was not altered under combined administration of 6-OHDA and single immobilization stress. These data suggest that an activation of the adrenergic system can potentiate gene expression of the cardiac NCX.     

Retinal pigment epithelium lipofuscin proteomics

Lipofuscin accumulates with age in the retinal pigment epithelium (RPE) in discrete granular organelles and may contribute to age-related macular degeneration. Because previous studies suggest that lipofuscin contains protein that may impact pathogenic mechanisms, we pursued proteomics analysis of lipofuscin. The composition of RPE lipofuscin and its mechanisms of pathogenesis are poorly understood in part because of the heterogeneity of isolated preparations. We purified RPE lipofuscin granules by treatment with proteinase K or SDS and showed by light, confocal, and transmission electron microscopy that the purified granules are free of extragranular material and associated membranes. Crude and purified lipofuscin preparations were quantitatively compared by (i) LC MS/MS proteomics analyses, (ii) immunoanalyses of oxidative protein modifications, (iii) amino acid analysis, (iv) HPLC of bisretinoids, and (v) assaying phototoxicity to RPE cells. From crude lipofuscin preparations 186 proteins were identified, many of which appeared to be modified. In contrast, very little protein ( approximately 2% (w/w) by amino acid analysis) and no identifiable protein were found in the purified granules, which retained full phototoxicity to cultured RPE cells. Our analyses showed that granules in purified and crude lipofuscin preparations exhibit no statistically significant differences in diameter or circularity or in the content of the bisretinoids A2E, isoA2E, and all-trans-retinal dimer-phosphatidylethanolamine. The finding that the purified granules contain minimal protein yet retain phototoxic activity suggests that RPE lipofuscin pathogenesis is largely independent of associated protein. The purified granules also exhibited oxidative protein modifications, including nitrotyrosine generated from reactive nitrogen oxide species and carboxyethylpyrrole and iso[4]levuglandin E(2) adducts generated from reactive lipid fragments. This finding is consistent with previous studies demonstrating RPE lipofuscin to be a potent generator of reactive oxygen species and supports the hypothesis that such species, including reactive fragments from lipids and retinoids, contribute to the mechanisms of RPE lipofuscin pathogenesis.     

Role of plasma membrane Ca2+-ATPase in contraction-relaxation processes of the bladder: evidence from PMCA gene-ablated mice

We investigated the roles and relationships of plasma membrane Ca²⁺-ATPase (PMCA), sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA)2, and Na⁺/Ca²⁺ exchanger (NCX) in bladder smooth muscle contractility in Pmca-ablated mice: Pmca4-null mutant (Pmca4^–/–) and heterozygous Pmca1 and homozygous Pmca4 double gene-targeted (Pmca1^+/–Pmca4^–/–) mice. Gene manipulation did not alter the amounts of PMCA1, SERCA2, and NCX. To study the role of each Ca²⁺ transport system, contraction of circular ring preparations was elicited with KCl (80 mM) plus atropine, and then the muscle was relaxed with Ca²⁺-free physiological salt solution containing EGTA. We measured the contributions of Ca²⁺ clearance components by inhibiting SERCA2 (with 10 µM cyclopiazonic acid) and/or NCX (by replacing NaCl with N-methyl-D-glucamine/HCl plus 10 µM KB-R7943). Contraction half-time (time to 50% of maximum tension) was prolonged in the gene-targeted muscles but marginally shortened when SERCA2 or NCX was inhibited. The inhibition of NCX significantly inhibited this prolongation, suggesting that NCX activity might be augmented to compensate for PMCA4 function in the gene-targeted muscles under nonstimulated conditions. Inhibition of SERCA2 and NCX as well as gene targeting all prolonged the relaxation half-time. The contribution of PMCA to relaxation was calculated to be 25–30%, with that of SERCA2 being 20% and that of NCX being 70%. PMCA and SERCA2 appeared to function additively, but the function of NCX might overlap with those of other components. In summary, gene manipulation of PMCA indicates that PMCA, in addition to SERCA2 and NCX, plays a significant role in both excitation-contraction coupling and the Ca²⁺ extrusion-relaxation relationship, i.e., Ca²⁺ homeostasis, of bladder smooth muscle. ATP2B; sarco(endo)plasmic reticulum Ca²⁺-ATPase 2; Na⁺/Ca²⁺ exchanger; homeostasis     

Intermediate filaments in muscle and epithelial cells of nematodes

Current concepts of the developmentally controlled multigene family of intermediate filament (IF) proteins expect the origin of their complexity in evolutionary precursors preceding all vertebrate classes. Among invertebrates, however, firm ultrastructural as well as molecular documentation of IFs is restricted to some giant axons and to epithelia of a few molluscs and annelids. As Ascaris lumbricoides is easily dissected into clean tissues, IF expression in this large nematode was analyzed by electron microscopic and biochemical procedures and a monoclonal antibody reacting with all mammalian IF proteins. We document for the first time the presence of IFs in muscle cells of an invertebrate. They occur in three muscle types (irregular striated pharynx muscle, obliquely striated body muscle, uterus smooth muscle). IFs are also found in the epithelia studied (syncytial epidermis, intestine, ovary, testis). Immunoblots on muscles, pharynx, intestine, uterus, and epidermis identify a pair of polypeptides (with apparent molecular masses of 71 and 63 kD) as IF constituents. In vitro reconstitution of filaments was obtained with the proteins purified from body muscle. In the small nematode Caenorhabditis elegans IF proteins are so far found only in the massive desmosome-anchored tonofilament bundles which traverse a special epithelial cell type, the marginal cells of the pharynx. We speculate that IFs may occur in most but perhaps not all invertebrates and that they may not occur in all cells in large amounts. As electron micrographs of the epidermis of a planarian--a member of the Platyhelminthes--reveal IFs, the evolutionary origin of this cytoplasmic structure can be expected either among the lowest metazoa or already in some unicellular eukaryotes.     

Volume occupation, environment, and accessibility in proteins. Environment and molecular area of RNase-S

The myosin light chains of cultured muscle cells and embryonic muscle tissue have been examined by two-dimensional gel electrophoresis. Myosin purified from primary cultures of rat muscle cells or the myogenic cell line L6 contain not only the light chains corresponding to those of fast twitch muscle but also another protein, differing slightly in molecular weight and isoelectric point from the adult LC1 protein. By a number of criteria this additional protein is shown to be a myosin light chain: (1) it is found in highly purified myosin preparations; (2) in L6 myosin it replaces the other LC1-type light chains in stoichiometric amounts; (3) it is part of the subfragment-1 complex of myosin produced by chymotrypsin. as expected for an LC1-type light chain. Total extracts of fused cultured muscle cells, when analyzed by two-dimensional electrophoresis, contain substantial amounts of this additional LC1-type protein, strongly suggesting that it is not a proteolytic fragment produced during myosin isolation. Unfused cultures do not synthesize detectable amounts of the adult light chains or the additional LC1-type light chain. This additional LC1 protein can be detected in embryonic or newborn muscle tissue but it is not present in adult myosin or myofibrils. These results indicate that a novel form of myosin light chain, referred to as an embryonic LC1 or LC1_emb, is characteristic of the early stages of muscle development.     

Expression in E. coli and purification of Thermus thermophilus translation initiation factors IF1 and IF3

The initiation of protein translation in bacteria requires in addition to mRNA, fMet-tRNA, and ribosomal subunits three protein factors, the initiation factor 1 (IF1), initiation factor 2 (IF2), and initiation factor 3 (IF3). The genes coding for IF1 and IF3 from Thermus thermophilus have been identified and cloned into pET expression vector and were expressed as soluble proteins in Escherichia coli. IF1 was purified by a DEAE-cellulose chromatography, followed by heat denaturation, chromatography on Hydroxylapatit, and gel permeation chromatography using Sephacryl 200HR. For the purification of IF3, a heat denaturation step is followed by anion-exchange chromatography on Q-Sepharose FF and gel permeation chromatography on Sephacryl 200HR. Using these procedures we obtained chromatographically pure and biologically active preparations of both T. thermophilus IF1 and IF3.     

m-Calpain-mediated cleavage of Na+/Ca2+ exchanger-1 in caveolae vesicles isolated from pulmonary artery smooth muscle

Using m-calpain antibody, we have identified two major bands corresponding to the 80 kDa large and the 28 kDa small subunit of m-calpain in caveolae vesicles isolated from bovine pulmonary artery smooth muscle plasma membrane. In addition, 78, 35, and 18 kDa immunoreactive bands of m-calpain have also been detected. Casein zymogram studies also revealed the presence of m-calpain in the caveolae vesicles. We have also identified Na⁺/Ca²⁺ exchanger-1 (NCX1) in the caveolae vesicles. Purification and N-terminal sequence analyses of these two proteins confirmed their identities as m-calpain and NCX1, respectively. We further sought to determine the role of m-calpain on calcium-dependent proteolytic cleavage of NCX1 in the caveolae vesicles. Treatment of the caveolae vesicles with the calcium ionophore, A23187 (1 μM) in presence of CaCl₂ (1 mM) appears to cleave NCX1 (120 kDa) to an 82 kDa fragment as revealed by immunoblot study using NCX1 monoclonal antibody; while pretreatment with the calpain inhibitors, calpeptin or MDL28170; or the Ca²⁺ chelator, BAPTA-AM did not cause a discernible change in the NCX protein profile. In vitro cleavage of the purified NCX1 by the purified m-calpain supports this finding. The cleavage of NCX1 by m-calpain in the caveolae vesicles may be interpreted as an important mechanism of Ca²⁺ overload, which could arise due to inhibition of Ca²⁺ efflux by the forward-mode NCX and that could lead to sustained Ca²⁺ overload in the smooth muscle leading to pulmonary hypertension.     

Single and multiple early afterdepolarization caused by nickel in rat atrial muscle

We examined the possible role of the Na-Ca exchange (NCX) in the arrhythmogenesis in rat atrial preparations applying microelectrode technique. In control Tyrode solution preparations isolated from the sinoatrial area contracted with frequency of 48+/-4 min(-1) (group I) or 84+/-7 min(-1) (group II). In preparation beating with low frequency partial inhibition of NCX by administration of Ni2+ (0.3 mmol/l) to the bath solution caused single early afterdepolarization (EAD) on the 15th min. During the following five minutes they were transformed into multiple EADs from 4 to 47 (action potentials) with general duration of 1-12 s. The effects were reversible. Ni2+ (0.3 mmol/l) in the preparations beating with higher rate (group II) did not cause multiple EADs, but after higher Ni2+ concentration (0.5 mmol/l) single EAD was observed more often. It was concluded that Ca2+ overload due to partial block of the NCX can contribute to the development of atrial tachyarrhythmias.     

Subunit interaction of rabbit muscle phosphofructokinase: effects of purification procedures

Structural, physical, and kinetic properties of rabbit muscle phosphofructokinase (PFK) purified by three different procedures were monitored in order to determine the effect of various purification procedures on the dynamics of subunit interaction. PFK was purified by three commonly used procedures: (1) differential heat precipitation [Kemp, R. G. (1972) Methods Enzymol. 42, 71-77], (2) differential heat and alcohol precipitation [Ling, R. H., Marcus, F., & Lardy, H. A. (1965) J. Biol. Chem. 240, 1893-1899], and (3) differential salt fractionation [Hesterberg, L. K., & Lee, J. C. (1980) Biochemistry 19, 2030-2039]. The physical, kinetic, and structural properties of these three preparations show that these proteins are not identical. Sedimentation velocity studies show that PFK purified by method 3 self-associates rapidly and that the system is thermodynamically homogeneous. The presence of an inactive or noninteracting component is not observed within an 8-h time limit. In contrast, PFK purified by method 1 or 2 is heterogeneous. In these preparations, a slowly sedimenting, noninteracting, inactive form of PFK is present. The remaining active protein is not stable but continuously converts to an inactive form. Active PFK can be fractionated from this inactive form by sedimentation. This active fraction behaves as a thermodynamically homogeneous system, and the subunits undergo rapid association-dissociation in a manner similar to PFK purified by method 3. Kinetic studies on these three preparations show that the inclusion of a heat and/or alcohol step in the purification procedure yields an enzyme that is less stable, has a lower specific activity, requires DTT for full activation, and is more susceptible to inhibition by ATP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chemical analysis of atherosclerotic plaque cholesterol combined with histology of the same tissue

Sensitive method for chemical analysis of free cholesterol (FC) and cholesterol esters (CE) was developed. Mouse arteries were dissected and placed in chloroform-methanol without tissue grinding. Extracts underwent hydrolysis of cholesteryl esters and derivatization of cholesterol followed by liquid chromatography/mass spectrometry (LC/MS/MS) analysis. We demonstrated that FC and CE could be quantitatively extracted without tissue grinding and that lipid extraction simultaneously worked for tissue fixation. Delipidated tissues can be embedded in paraffin, sectioned, and stained. Microscopic images obtained from delipidated arteries have not revealed any structural alterations. Delipidation was associated with excellent antigen preservation compatible with traditional immunohistochemical procedures. In ApoE(-/-) mice, LC/MS/MS revealed early antiatherosclerotic effects of dual PPARalpha,gamma agonist LY465606 in brachiocephalic arteries of mice treated for 4 weeks and in ligated carotid arteries of animals treated for 2 weeks. Reduction in CE and FC accumulation in atherosclerotic lesions was associated with the reduction of lesion size. Thus, a combination of LC/MS/MS measurements of CE and FC followed by histology and immunohistochemistry of the same tissue provides novel methodology for sensitive and comprehensive analysis of experimental atherosclerotic lesions.     

Sperm-specific C-terminal processing of the proteasome PSMA1/α6 subunit

We previously reported that the ascidian sperm proteasome degrades the egg-coat protein extracellularly during fertilization. In order to explore an extracellular transport signal, we purified the proteasome from ascidian sperm and compared its subunit structure with egg and muscle proteasomes. The results showed that PSMA1/α6 subunit of the sperm proteasome is distinct from egg and muscle proteasomes. LC/MS/MS analysis revealed that the C-terminal 16 residues of sperm α6 subunit are processed. Whereas sperm-specific paralogous genes of α subunits are reported, its sperm-specific C-terminal processing is a newly discovered novel post-translational modification of the proteasome.