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alters cardiac metabolism
1Department of Cardiac and Vascular Sciences and 2Department of Basic Medical Sciences, St. George's Hospital Medical School, London SW17 0RE, United Kingdom; 3Institute of Medical Biology and Human Genetics, University of Innsbruck, Innsbruck 6020, Austria; 4Max-Planck-Institute for Experimental Endocrinology, Hannover 30625, Germany; and 5Proteome Sciences and 6Institute of Psychiatry, King's College, London SE5 8AF, United Kingdom
Submitted 11 September 2003 ; accepted in final form 15 January 2004
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ABSTRACT |
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 TOP ABSTRACT EXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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is believed to play an essential role in cardiomyocyte growth. In the present study, we investigated the effect of PKC- on cardiac metabolism using PKC- knockout mice generated in our laboratories. Proteomic analysis of heart protein extracts revealed profound changes in enzymes related to energy metabolism: certain isoforms of glycolytic enzymes, e.g., lactate dehydrogenase and pyruvate kinase, were absent or decreased, whereas several enzymes involved in lipid metabolism, e.g., phosphorylated isoforms of acyl-CoA dehydrogenases, showed a marked increase in PKC-–/– hearts. Moreover, PKC- deficiency was associated with changes in antioxidants, namely, 1-Cys peroxiredoxin and selenium-binding protein 1, and posttranslational modifications of chaperones involved in cytoskeleton regulation, such as heat shock protein (HSP)20, HSP27, and the 
-subunit of the cytosolic chaperone containing the T-complex polypeptide 1. High-resolution NMR analysis of cardiac metabolites confirmed a significant decrease in the ratio of glycolytic end products (alanine + lactate) to end products of lipid metabolism (acetate) in PKC-–/– hearts. Taken together, our data demonstrate that loss of PKC- causes a shift from glucose to lipid metabolism in murine hearts, and we provide a detailed description of the enzymatic changes on a proteomic level. The consequences of these metabolic alterations on sensitivity to myocardial ischemia are further explored in the accompanyingpaper (20).
protein kinase C; proteomics; nuclear magnetic resonance; mouse model; metabolomics
, 
, and 
), novel PKCs (, 
, 
, and 
), and atypical PKCs ( and 
) (25). Novel PKC isoforms are maximally activated by diacylglycerol in the absence of calcium, and recent evidence suggests a cross-regulation of novel PKC isoforms in cardiomyocytes (29). PKC- and PKC- are among the predominant isoforms of PKC in cardiac ventricles and have been implicated in heart failure, myocardial hypertrophy, and ischemic preconditioning (6, 9, 16).
Most of our knowledge about the role of PKC is derived from studies using a variety of inhibitors, many of which are not isoform specific and inhibit, to varying degrees, other protein kinases. Notably, the specificity of rottlerin, a widely used PKC- inhibitor, has recently been questioned (32): rottlerin appears to block PKC- activity indirectly in vivo by uncoupling mitochondria. Additionally, PKC isoform translocation is considered a hallmark of PKC activation. PKC-, however, is most efficiently tyrosine-phosphorylated among the PKC family, and phosphorylation is required for optimal PKC- activation in cardiomyocytes (10). Importantly, tyrosine phosphorylation and activation of PKC- without translocation has been observed after hydrogen peroxide stimulation (26). This finding suggests that translocation is an imperfect surrogate marker for PKC- activation and raises questions as to whether inhibition of PKC- translocation results in complete inhibition of PKC--specific effects. Therefore, previous studies, especially on the PKC- isoform, have to be interpreted with caution.
To study the role of PKC- in cardiac tissues without using isozyme-nonselective chemical compounds or translocation inhibitors, we have recently created the first knockout mice lacking PKC- (11). We now combine the advantages of gene targeting and proteomic and metabolomic analysis to clarify the functional consequences of mutational ablation of the PKC- gene in cardiac tissues. By comparing the protein and metabolite profiles of wild-type and knockout hearts, we demonstrate PKC--associated alterations in the proteome and provide firm evidence that hearts lacking PKC- show a metabolic shift from glycolysis toward increased fatty acid oxidation.
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EXPERIMENTAL PROCEDURES |
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TOPABSTRACTEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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-deficient (PKC-–/–) mice were generated by targeted disruption of the endogenous PKC- gene. Genotypic characterization of adult mice by Southern blot analysis of genomic DNA indicated the successfully mutated allele (11). Systolic blood pressure and heart rate were measured using a noninvasive computerized tail-cuff system (BP-2000, Harvard Instruments). Mice were trained for 7 days by measuring blood pressure daily, after which blood pressure and heart rate were measured and recorded for 5 consecutive days. Additionally, blood pressure measurements were obtained by cannulating the carotid artery: mice underwent light anesthesia with thiopental (40 mg/kg im) followed by insertion of polyethylene catheters via the common carotid artery (34). The arterial catheter was connected to a pressure transducer (COBE; Lakewood, CO) and a blood pressure analyzer (Micro-MED; Louisville, KY). Measurements were recorded every 30 s for 10 min. Proteomic analysis of heart tissue. Heart tissues for proteomic and metabolomic analysis were rinsed thoroughly with cold PBS to remove any blood components within the heart chambers, and whole hearts were frozen immediately in liquid nitrogen to avoid protein or metabolite degradation. The procedure used for proteomic analysis has been described previously (4, 21). Frozen heart samples were pulverized under liquid nitrogen into a fine powder. The resulting powder was homogenized in lysis buffer [containing 9.5 M urea, 2% (wt/vol) CHAPS, 0.8% (wt/vol) Pharmalyte pH 3–10, and 1% (wt/vol) DTT plus protease inhibitors] and centrifuged at 13,000 g at 20°C for 10 min. The supernatant was harvested, and protein concentration was determined. Solubilized samples were divided into aliquots and stored at –80°C. For two-dimensional (2-D) gel electrophoresis, extracts were loaded on nonlinear immobilized pH gradient (IPG) 18-cm strips (3–10, Amersham Pharmacia Biotech). For analytic and preparative gels, respectively, a protein load of 100 and 400 µg was applied to each IPG strip using an in-gel rehydration method. Samples were diluted in rehydration solution [containing 8 M urea, 0.5% (wt/vol) CHAPS, 0.2% (wt/vol) DTT, and 0.2% (wt/vol) Pharmalyte pH 3–10] and rehydrated overnight in a reswelling tray. Strips were focused at 0.05 mA/IPG strip for 60 kV·h at 20°C. Once isoelectric focusing was completed, the strips were equilibrated in 6 M urea containing 30% (vol/vol) glycerol, 2% (wt/vol) SDS, and 0.01% (wt/vol) bromphenol blue with the addition of 1% (wt/vol) DTT for 15 min, followed by the same buffer without DTT but with the addition of 4.8% (wt/vol) iodoacetamide for 15 min. SDS-PAGE was performed using 12% T, 2.6% C separating polyacrylamide gels without a stacking gel, using the Hoefer DALT system. The second dimension was carried out overnight at 20 mA/gel at 8°C and was terminated when the bromphenol dye front had migrated off the lower end to the gels. After electrophoresis, gels were fixed for a minimum of 1 h in methanol-acetic acid-water solution [4:1:5 (vol/vol/vol)]. 2-D gel electrophoresis protein profiles were visualized in preparative gels by silver staining using the Plus One silver staining kit (Amersham Pharmacia Biotech) with slight modifications to ensure compatibility with subsequent mass spectroscopy (MS) analysis (35). Analytic gels were stained with a more sensitive silver staining kit (Owl, UK). For the detection of phosphoproteins, 2-D electrophoresis gels were stained with Pro-Q Diamond (Molecular Probes) according to the manufacturer's instruction and scanned on a Typhoon 9400 scanner (Amersham Biosciences) at 532 nm, with the emission filter set at 560 LP and the photomultiplier tube set at 600 V. Counterstaining was performed with Sypro Ruby (Molecular Probes). Spot patterns were analyzed using Progenesis (Nonlinear Dynamics), Proteomweaver (Definiens), and PDQuest software (Bio-Rad). Spots showing a statistical difference in intensity were excised for identification.
Mass spectrometry.
Gel pieces containing selected protein spots were treated overnight with modified trypsin (Promega) according to a previously published protocol (31). Peptide fragments were recovered by sequential extractions with 50 mM ammonium hydrogen carbonate, 5% (vol/vol) formic acid, and acetonitrile 50% (vol/vol). Extracts were lyophilized, resuspended in 20 µl of 0.1% (vol/vol) trifluoroacetic acid-10% (vol/vol) acetonitrile, and desalted on Millipore Zip tips according to the manufacturer's instructions. Matrix-assisted laser desorption/ionization-MS was performed using an Axima CFR spectrometer (Kratos; Manchester, UK). The instrument was operated in the positive ion reflectron mode. -Cyano-4-hydroxy-cinnaminic acid was applied as the matrix. Spectra were internally calibrated using trypsin autolysis products. The resulting peptide masses were searched against databases using the MASCOT program (27). One missed cleavage per peptide was allowed, and carbamidomethylation of cysteine as well as partial oxidation of methionine were assumed. In addition to MALDI-MS, tandem MS was performed for the sequencing of tryptic digest peptides. After enzymatic degradation, peptides were separated by capillary liquid chromatography on a reverse-phase column (BioBasic-18, 100 x 0.18 mm, particle size 5 µm, Thermo Electron) and applied to a LCQ ion-trap mass spectrometer (LCQ Deca XP Plus, Thermo Finnigan). Spectra were collected from the ion-trap mass analyzer using full ion scan mode over the mass-to-charge (m/z) range of 300–2,000. MS-MS scans were performed on each ion using dynamic exclusion. A database search was performed using the TurboSEQUEST software (Thermo Finnigan).
RT-PCR. Total RNA from heart tissues was extracted using the Fast RNA kit according to the protocol provided by the manufacturer (Qiagen). Total RNA (2 µg) was reverse transcribed into cDNA using the Promega RT system. The RT products were examined by PCR with 1-Cys peroxiredoxin (1-Cys prx) primers producing 203-bp fragments (24) and GAPDH primers producing 309-bp fragments.
Western blotting. Western blotting was performed as described previously (13, 14). For immunoblotting of 2-D electrophoresis gels, 100 µg of protein were loaded on nonlinear IPG 7-cm strips (3–10, Amersham Pharmacia Biotech) by active rehydration (30 V, 12 h) and focused for 13 kV·h using the IPG phor system (Amersham Pharmacia Biotech). After being focused, the strips were equilibrated as described above, separated on 4–12% Tris-glycine zoom gels (Invitrogen), and blotted onto nitrocellulose membranes. Antibodies to the cytosolic chaperone containing the T-complex polypeptide (CCT) subunits were kindly provided by Dr. A. Roobol (University of Kent, Canterbury, UK).
Proton NMR spectroscopy. Snap-frozen hearts were extracted in 6% perchloric acid (1). Neutralized extracts were freeze dried and reconstituted in D2O. Extracts (0.5 ml) were placed in 5-mm NMR tubes. 1H NMR spectra were obtained using a Bruker 500-MHz spectrometer. The water resonance was suppressed by using gated irradiation centered on the water frequency. Sodium 3-trimethylsilyl-2,2,3,3-tetradeuteropropionate (TSP) was added to the samples for chemical shift calibration and quantification. Immediately before the NMR analysis, the pH was readjusted to 7 with PCA or KOH.
Statistical analysis. Statistical analysis was performed using ANOVA and Student's t-test, respectively. Results are given as means ± SD. A P value of <0.05 was considered significant.
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RESULTS |
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TOPABSTRACTEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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–/– mice were indistinguishable from their wild-type littermates; they developed normally and were fertile. The null allele was confirmed by the absence of PKC- expression in a variety of tissues, including the heart (11). PKC-–/– mice showed no overt cardiac phenotype and no significant differences in physiological variables, such as body weight, heart rate, and arterial blood pressure (measured by the cuff technique as well as by cannulating the carotid artery; Table 1). The heart weight-to-body weight ratio was slightly lower in PKC-–/– mice; however, this difference failed to reach statistical significance (P = 0.24; Table 1).
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–/– hearts.
To provide insights into the potential cellular targets of PKC-, we analyzed the changes in the proteome by 2-D gel electrophoresis. Average gels for PKC-+/+ and PKC-–/– hearts were created from 4 gels/group. A direct overlay is presented in Fig. 1. With the use of a broad-range pH gradient (pH 3–10 nonlinear), 2-D electrophoresis gels compromised 
1,400 protein features. Differentially expressed spots were highlighted in color (orange and blue indicate an increase in PKC-+/+ and PKC-–/– hearts, respectively; Fig. 1). Numbered spots were excised and subject to in-gel tryptic digestion. Protein identifications as obtained by MALDI-MS are listed in Table 2.
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–/– hearts were related to energy metabolism. Enzymes involved in glycolysis, e.g., isoforms of glycerol-3-phosphate dehydrogenase, pyruvate kinase, and lactate dehydrogenase, were less abundant compared with wild-type controls, whereas certain enzymatic species related to lipid metabolism were found to be markedly upregulated in PKC-–/– hearts: a three- and fivefold increase was observed for two isoforms of acyl-CoA dehydrogenase, which are responsible for -oxidation of short-chain fatty acids. However, their isoelectric points (pI) in 2-D electrophoresis gels were very different from the calculated one (Table 2), and subsequent staining for phosphoproteins demonstrated that these isoforms are highly phosphorylated (Fig. 2A). Similarly, propionyl-CoA carboxylase, an enzyme involved in fatty acid metabolism, appeared as a row of several spots with different pI and the same molecular mass in PKC-–/– hearts (Fig. 1), indicating again altered posttranslational modifications rather than changes in protein expression. Concomitantly, aldehyde deydrogenase 4 family member A1 and Ke 6 protein were found to be present in more acidic isoforms in PKC-–/– hearts (Fig. 1). The acidic shift of aldehyde deydrogenase 4 family member A1 in PKC-–/– hearts was associated with the presence of a mitochondrial precursor sequence (Fig. 2B). Notably, this enzymatic precursor was not expressed at detectable levels in PKC-+/+ hearts. Taken together, our proteomic data suggest increased lipid metabolism in PKC-–/– hearts.
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–/– hearts.
Another interesting observation in our proteomic analysis was the absence of the oxidized form of 1-Cys prx in PKC-–/– hearts (Fig. 3A). Peroxiredoxins represent a special type of peroxidases as the protein is the reducing substrate itself; upon oxidative stress, the active site in 1-Cys prx is either oxidized to cysteine sulfenic acid or overoxidized to cysteine sulfonic acid. While the first modification is DTT sensitive and therefore undetectable in 2-D electrophoresis gels, the latter modification is DTT resistant and results in a charge shift toward a more acidic pI (33). Thus 1-Cys prxs are often encountered as doublet spots in 2-D electrophoresis. Interestingly, 1-Cys prx was exclusively present as a DTT sensitive (basic) isoform in PKC-–/– hearts, whereas the predominant isoform in wild-type hearts was the DTT insensitive (acidic) one, corresponding to overoxidation of the active site cysteine into a cysteine sulfonic acid (Fig. 3A).
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–/– hearts, RT-PCR showed higher levels of 1-Cys prx mRNA, indicating an increased turnover of this antioxidant protein compared with PKC-–/– hearts (Fig. 3B). Total protein levels of 1-Cys prx were almost twofold decreased in PKC-–/– hearts, as estimated by quantification on 2-D electrophoresis gels (Fig. 3A; signal intensity 4,055 vs. 2,179 arbitrary units). Similarly, expression of selenium-binding protein 1, another protein related to protection against oxidative stress, was altered in PKC-–/– hearts (Table 2).
Changes in chaperones in PKC-–/– hearts.
Previous findings in PKC- transgenic mice demonstrated that inhibition of PKC- translocation resulted in focal cytoskeletal disruption and upregulation of crystallin-/B (6), the most abundant small heat shock protein (HSP) in cardiac tissue. In PKC-–/– hearts, no quantitative difference in crystallin-/B expression was observed (Fig. 4A), but a protein similar to HSP 20 was found to be present in a more basic isoform compared with PKC-+/+ hearts (Fig. 4B, spots 17a and 17b). Its identification was confirmed by tandem MS (Fig. 4C). A common modification causing such pI changes on 2-D gels is dephosphorylation: whereas phosphorylated HSP20 is proposed to interact with monomeric actin, dephosphorylated forms of HSP20 bind to polymeric actin. HSP20 may also form heterocomplexes with other HSPs, including crystallin-/B.
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-subunit of CCT-1 were differentially expressed in PKC-–/– hearts (Table 2). Because no differences in protein abundance were observed in Western blots of one-dimensional gels (Fig. 5A), we verified our findings by immunoblotting of 2-D gels. HSP27 was visualized as a charge train consisting of three major spots (Fig. 5B), which are known to represent different phosphorylation states. The most acidic (and most phosphorylated) spot of HSP27 was less abundant in PKC-–/– hearts (Fig. 5B, bottom). This is in excellent agreement with our findings in 2-D gels, where spot 18 was identified as HSP27 with an estimated pI of 5.4 compared with the theoretical value of 6.4.
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(18), there has been no evidence so far that PKC- plays a role in regulating CCT-1. CCT-1 is a heterooligomeric complex of eight different subunits. Its folding substrate specificity is mainly restricted to actin and tubulin, with the -subunit being involved in tubulin binding (17). Immunoblotting of 2-D gels revealed that the most basic isoform of CCT- was absent in PKC-–/– hearts, whereas no differences were observed for other subunits (Fig. 5, C and D). Thus changes in 2-D gels represented no differences in protein abundance but reflected altered posttranslational modification.
Metabolic changes in PKC-–/– hearts.
Enzymatic changes constituted by far the majority of differences in the protein profile of PKC-–/– hearts. To clarify the metabolic net effect of these proteomic changes, we measured cardiac metabolites with high-resolution NMR spectroscopy (Fig. 6) (5). Within the aliphatic region (–0.05 to 4.2 ppm) of the NMR spectra, resonances have been assigned to -ketoisovalerate, lactate, alanine, acetate, glutamate, succinate, creatine, choline, carnitine, taurine, and glycine (5). The presence of glycerophosphocholine within the carnitine peak was ruled out by NMR analysis at low pH. NMR spectra of PKC-+/+ and PKC-–/– hearts are shown in Fig. 6, A and B. Metabolite concentrations were similar in wild-type and knockout hearts except for the ratio of glycolytic end products (alanine + lactate) to end products of lipid metabolism (acetate), which was significantly decreased in PKC-–/– hearts (Fig. 6C). Thus our metabolomic data confirm the functional relevance of the proteomic changes described above.
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DISCUSSION |
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TOPABSTRACTEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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activation is thought to be crucial in cardiac pathology, such as cardiac hypertrophy, heart failure, and ischemia-reperfusion injury (6, 9, 16). Accordingly, delineating the in vivo effects of PKC- in myocardial tissue is a scientific priority. So far, approaches to study PKC- activation in hearts have included the use of isozyme-nonselective inhibitors. In the present study, we investigated the role of PKC- in cardiac tissue by using PKC- knockout mice. Mutational ablation of the PKC- gene caused profound alterations in the proteome and metabolome, which resulted in a metabolic shift from glycolysis toward increased lipid metabolism. Considering the importance of energy metabolism in cardiac tissues, our findings could contribute to a better understanding of PKC- isoform specific effects in the pathological conditions mentioned above.
Altered energy generation in PKC-–/– hearts.
It has been demonstrated that PKC- and PKC- have overlapping functions in myocardial growth (3). This functional redundancy might explain why neither PKC-–/– nor PKC-–/– mice show an overt cardiac phenotype. However, expression levels of PKC- as studied by Western blot analysis were similar in PKC-+/+ and PKC-–/– hearts (data not shown). Interestingly, transgenic mice expressing a PKC- or PKC- translocation inhibitor developed lethal cardiomyopathies (6, 23), highlighting fundamental differences between these mouse models.
Our proteomic analysis demonstrates that several enzymatic isoforms related to glucose metabolism were absent in PKC-–/– hearts. This is in line with a recent report by Caruso et al. (2) suggesting that PKC- is required for insulin stimulation of the pyruvate dehydrogenase complex in L6 skeletal muscle cells and immortalized mouse hepatozytes. Pyruvate dehydrogenase catalyzes the oxidation of pyruvate to acetyl-CoA, which represents the irreversible step from glycolysis to the tricarboxylic acid cycle. Altered activitiy of the pyruvate dehydrogenase complex is a likely explanation for the observed changes in glycolytic enzymes in our proteomic analysis.
Interestingly, enzymes related to lipid metabolism, i.e., phosphorylated isoforms of acyl-CoA dehydrogenases, were more abundant in PKC-–/– hearts. To translate such findings into a functional context is a common problem of proteomic analysis because differences at the protein level do not necessarily allow any conclusions about enzymatic activity. In the present study, we demonstrated that NMR analysis is a powerful tool to reveal the metabolic net effect of proteomic changes: the observed decrease in the ratio of glycolytic end products to end products of lipid metabolism suggests that increased fatty acid oxidation might compensate for impaired glycolysis in PKC-–/– hearts, supporting our proteomic findings. Therefore, our study provides the first evidence that loss of PKC- is associated with increased lipid metabolism, which would contribute to the inhibition of the pyruvate dehydrogenase complex.
Antioxidants in PKC-–/– hearts.
PKC- is activated by hydrogen peroxide and has been suggested as a sensor of oxidative stress (8). Our proteomic analysis showed altered expression of antioxidant proteins in PKC-–/– hearts. First, total protein levels and de novo synthesis of 1-Cys prx were decreased in PKC-–/– hearts. This is consistent with a previous report (12) showing that PKC- is required for transcriptional activation of peroxiredoxin 1, another member of the peroxiredoxin family. Second, 1-Cys prx was only present in its reduced form in PKC-–/– hearts despite its importance for the detoxification of phospholipid hydroperoxides as well as organic peroxides (derived from short-chain organic fatty acids) (19). This observation is consistent with our previous finding: that loss of PKC- is associated with decreased oxidative stress in vascular smooth muscle cells (11). Third, apart from 1-Cys prx, selenium-binding protein 1, which accomplishes the intracellular transport of the trace element (30), was differentially expressed in PKC-–/– hearts. The amino acid selenocysteine is present in various redox enzymes, including the active site of thioredoxin reductase and glutathione peroxidase, which scavenges hydrogen peroxide (7). Thus by modulating the cellular oxidative status, PKC- deficiency influences antioxidant expression in murine hearts.
Altered chaperones.
Among the PKC- family, PKC- and, to a lesser extent, PKC-, appear to be the most effective HSP kinases (18). Our findings in PKC-–/– mice provide evidence that posttranslational modifications of three chaperones, namely, HSP20, HSP27, and the -subunit of CCT-1, are dependent on PKC-. All these chaperones are associated with cytoskeleton function by regulating actin and tubulin polymerization. That PKC- activity is required for cytoskeletal integrity has been suggested previously: transgenic mice overexpressing a PKC- translocation inhibitor developed myofibrillar cardiomyopathy in a dose-dependent fashion, which was characterized by focal cytoskeletal disruption, upregulation of crystalline /B, and the formation of protein aggregates containing mitochondria (6). Interestingly, small HSPs guard the cytoskeleton from stressful stimuli by phosphorylation-dependent mechanisms and protect cardiomyocytes against oxidative stress (15).
Knockout mice.
Recently, we (11) and another group (22) independently developed mice deficient in PKC-. Both studies demonstrated that knockout mice developed normally and were fertile. Although PKC- is proposed to act as a tumor suppressor, no obvious increase of cancer-induced death was observed. Whereas we observed an abnormal accumulation of vascular smooth muscle cells and accelerated arteriosclerosis in PKC--deficient vein grafts (11), Miyamato et al. (22) showed increased proliferation of B lymphocytes and loss of B cell tolerance in PKC- null mice. Given the wide distribution of PKC- in cells and tissues, it was rather unexpected that PKC-–/– mice showed a clear phenotype only in certain cells. In the present study, we characterized the metabolic effects of PKC- deficiency, which are likely to be relevant for most insulin-sensitive tissues.
In conclusion, we have provided evidence that PKC- deficiency is associated with increased lipid metabolism in cardiac tissues. To the best of our knowledge, our study is the first to characterize proteomic as well as metabolomic changes in the same animal model. Our findings could be important for a better understanding of PKC--induced signaling and could lead to new therapeutic strategies for PKC--related diseases.
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TOPABSTRACTEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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REFERENCES |
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TOPABSTRACTEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONGRANTSREFERENCES |
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-protein kinase C inhibitor and -protein kinase C activator. Circulation 108: 869–875, 2003. and - isoforms. Am J Physiol Heart Circ Physiol 281: H404–H410, 2001. null mice. Am J Physiol Heart Circ Physiol: H946–H956, 2004.
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