Combined exposure to manganese and iron decreases oxidative stress-induced nerve damage by increasing Nrf2/HO-1/NQO1 expression.

BACKGROUND: Manganese (Mn) and iron (Fe) are essential trace elements for humans, yet excessive exposure to Mn or Fe can accumulate in the central nervous system (CNS) and cause neurotoxicity. The purpose of this study was to investigate the effects of Mn and Fe exposure, alone or in combination, on inducing oxidative stress-induced neurological damage in rat cortical and SH-SY5Y cells, and to determine whether combined exposure to these metals increases their individual toxicity. METHODS: SH-SY5Y cells and male Sprague-Dawley rats were used to observe the effects of oxidative stress-induced neurological damage induced by exposure to manganese and iron alone or in combination. To detect the expression of anti-oxidative stress-related proteins, Nrf2, HO-1, and NQO1, and the apoptosis-related proteins, Bcl2 and Bax, and the neurological damage-related protein, α-syn. To detect reactive oxygen species generation and apoptosis. To detect the expression of the rat cortical protein Nrf2. To detect the production of proinflammatory cytokines. RESULTS: We demonstrate that juvenile developmental exposure to Mn and Fe and their combination impairs cognitive performance in rats by inducing oxidative stress causing neurodegeneration in the cortex. Mn, Fe, and their combined exposure increased the expression of ROS, Bcl2, Bax, and α-syn, activated the inflammatory factors IL-6 and IL-12, inhibited the activities of SOD and GSH, and induced oxidative stress-induced neurodegeneration both in rats and SH-SY5Y cells. Combined Mn-Fe exposure attenuated the oxidative stress induced by Mn and Fe exposure alone by increasing the expression of antioxidant factors Nrf2, HO-1, and NQO1. CONCLUSION: In both in vivo and in vitro studies, manganese and iron alone or in combination induced oxidative stress, leading to neuronal damage. In contrast, combined exposure to manganese and iron mitigated the oxidative stress induced by exposure to manganese and iron alone by increasing the expression of antioxidant factors. Therefore, studies to elucidate the main causes of toxicity and establish the molecular mechanisms of toxicity should help to develop more effective therapeutic modalities in the future.

Protective Effects of Sodium Para-Aminosalicylic Acid on Lead and Cadmium Co-Exposure in SH-SY5Y Cells.

BACKGROUND: Combined exposure to lead and cadmium is common in occupational environments. However, the effects of co-exposure to Pb-Cd on neurotoxicity have not been fully clarified. Sodium para-aminosalicylic acid (PAS-Na) has previously been shown to protect neurons from Pb-induced toxicity. This study aimed to investigate the beneficial effect of PAS-Na against co-exposure to Pb-Cd-induced neurodegeneration in SH-SY5Y cells. METHODS: The MTT assay was used to detect the effects of Pb and Cd alone, or in combination, on SH-SY5Y cell survival. The effects of Pb and Cd alone or in combination on oxidative stress were assessed by reactive oxygen species (ROS) level. Nrf2, the master switch for antioxidant responses, was detected by immunofluorescence. Protein expression levels of PI3K, Akt, p-Akt, Nrf2 and HO-1 were determined by Western blot analysis. RESULTS: MTT assay results established that the survival rate of SH-SY5Y cells was not significantly affected by exposure to 1 µmol/L lead, 0.25 µmol/L cadmium, and 1-fold Pb-Cd mixture (1 µmol/L Pb + 0.25 µmol/L Cd), while 10-fold Pb-Cd combined exposure (10 µmol/L Pb + 2.5 µmol/L Cd) significantly reduced the survival rate of SH-SY5Y cells. Combined Pb-Cd exposure significantly increased intracellular ROS levels, and N-Acetyl-L-cysteine (NAC) treatment in the 10 µmol/L Pb + 2.5 µmol/L Cd group significantly decreased ROS expression levels, attenuating the levels of oxidative stress. Protein expression of PI3K and p-Akt significantly decreased in the 10 µmol/L Pb + 2.5 µmol/L Cd group, while the expression of PI3K and p-Akt protein increased after PAS-Na intervention. Immunofluorescence analysis showed that levels of Nrf2 in the nucleus increased in the 10 µmol/L Pb + 2.5 µmol/L Cd group, along with Nrf2 protein levels, suggesting that Nrf2 was translocated from the cytoplasm into the nucleus upon combined Pb-Cd exposure. In addition, HO-1 protein expression level, a downstream gene product of Nrf2, was increased. In response to NAC intervention, HO-1 protein expression levels significantly decreased. PAS-Na had the same intervention effect as NAC. CONCLUSION: Combined exposure to Pb-Cd induced oxidative stress and cytotoxicity in SH-SY5Y cells. PAS-Na displayed antagonistic effects on neurodegenerative changes induced by combined Pb-Cd exposure; hence, it may afford a novel treatment modality for exposure to these metals.

Comparison of Proteomics Profiles Between Xenografts Derived from Cell Lines and Primary Tumors of Thyroid Carcinoma.

Patient-consistent xenograft model is a challenge for all cancers but particularly for thyroid cancer, which shows some of the greatest genetic divergence between human tumors and cell lines. In this study, proteomic profiles of tumor tissues from patients, included anaplastic thyroid carcinoma (ATC) and papillary thyroid carcinoma, and xenografts (8305C, 8505C, FRO, BAPAP and IHH4) were obtained using HPLC-tandem mass spectrometry and compared based on all proteins detected (3,961), cancer-related proteins and druggable proteins using pairwise Pearson's correlation analysis. The human tissue showed low proteomic similarity to the ATC cell lines (8305C, r = 0.344-0.416; 8505C, 0.47-0.579; FRO, 0.267-0.307) and to PTC cell lines (BCPAP, 0.303-0.468; IHH4, 0.262-0.509). Human tissue showed the following similarity to cell lines at the level of 135 cancer-related pathways. The ATC cell lines contained 47.4% of the cancer-related pathways (19.26%-33.33%), while the PTC cell lines contained 40% (BCPAP, 25.93%; IHH4, 28.89%). In patient tumor tissues, 44-60 of 76 and 52-53 of 93 druggable proteins were identified in ATC and PTC tumors, respectively. Ten and 29 druggable proteins were not identified in any of the ATC and PTC xenografts, respectively. We provide a reference for CDX selecting in in vivo studies of thyroid cancer.

Destrin Contributes to Lung Adenocarcinoma Progression by Activating Wnt/ß-Catenin Signaling Pathway.

Lung cancer, especially lung adenocarcinoma, is one of the most common neoplasms worldwide. However, the mechanisms underlying its initiation, development, and metastasis are still poorly understood. Destrin (DSTN) is a member of ADF/cofilin family. Its detailed biological function remains unknown, although it is reported that DSTN is involved in cytoskeleton remodeling and regulation of actin filament turnover. Recent evidence has shown that high expression of cofilin-1 is associated with invasion and poor prognosis of several types of human tumors, but the detailed mechanism is still entirely unclear, particularly in lung cancer tumorigenesis and malignancy. Here, we report that DSTN was highly expressed in a mouse lung cancer model induced by urethane and in clinical lung adenocarcinoma tissue samples. Its expression level was positively correlated with cancer development, as well as metastasis to the liver and lymph nodes. Consistently, it was directly associated with the poor prognosis of lung adenocarcinoma patients. Furthermore, we also found that DSTN promotes cell proliferation, invasion, and migration in vitro, and facilitates subcutaneous tumor formation and lung metastasis via intravenous injection in vivo. Mechanically, DSTN associates with and facilitates nuclear translocation of ß-catenin, which promotes epithelial-to-mesenchymal transition (EMT). Taken together, our results indicated that DSTN enhances lung cancer malignancy through facilitating ß-catenin nuclear translocation and inducing EMT. Combined with multivariate analyses, DSTN might potentially serve as a therapeutic target and an independent prognostic marker of lung adenocarcinoma. IMPLICATIONS: This finding indicates that DSTN facilitates ß-catenin nuclear translocation and promotes malignancy in lung adenocarcinoma.

Elevated proportion of collapsed microvessels indicate poor survival outcome in patients with non-small cell lung cancer.

BACKGROUND: An integral and well-functioning vascular system is essential for tumor progression and chemotherapy infusion. However, the lumen integrity of the microvessels and its significance in prognosis has not been studied. In this study, we found that the proportion of collapsed microvessels is suggested to be a novel biomarker for predicting prognosis in patients with non-small cell lung cancer (NSCLC). METHODS: In this study, immunohistochemical CD31 staining was performed to identify the microvessels in tumor specimens. Proportions of collapsed vessels were estimated in CD31-stained tumor specimens from 100 patients with NSCLC. The correlation between collapsed microvessel proportion and survival time were evaluated by univariate and multivariate analysis. RESULTS: Data from 99 patients were analyzed and a wide range of collapse-microvessel fraction was observed in 96 patients (1.4%-70%). Elevated collapse proportion (⩾6.5%) indicated poor overall survival in both univariate analysis (p = 0.042) and multivariate analysis (p = 0.014). CONCLUSIONS: Elevated proportion of collapsed microvessels indicted poor survival outcome in patients with NSCLC.

Hyphobacterium indicum sp. nov., isolated from deep seawater, and emended description of the genus Hyphobacterium.

A novel aerobic, Gram-stain-negative bacterium, designated strain 2ED5T, was isolated from a deep seawater sample in the north-west Indian Ocean. Cells of the strain were oval- to rod-shaped, and motile by a polar flagellum or sessile by a prostheca. The strain formed creamy white colonies on 2216E marine agar plates. It grew at 10-40 °C (optimum 28 °C) and pH 5.0-8.0 (optimum pH 6.0-7.0). The strain required 1-6 % (w/v) NaCl for growth and grew optimally in the presence of 2-3 % NaCl. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain 2ED5T was affiliated with the genus Hyphobacterium in the family Hyphomonadaceae of the class Alphaproteobacteria, sharing 95.1 % similarity at the 16S rRNA gene sequence level with the type strain of Hyphobacterium vulgare, the only species in the genus Hyphobacterium. The major fatty acids of the strain were C18 : 1ω7c and iso-C17 : 1ω9c, and the polar lipids included monoglycosyl diglyceride, sulfoquinovosyl diacylglycerol, glucuronopyranosyl diglyceride, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and an unidentified glycolipid. The strain contained ubiquinone Q-10 as the predominant respiratory quinone. The G+C content of the genomic DNA of the strain was 60.9 mol%. Based on the results of this polyphasic analysis, strain 2ED5T represents a novel species in the genus Hyphobacterium, for which the name Hyphobacterium indicum sp. nov. is proposed. The type strain is 2ED5T (=CGMCC 1.16466T=JCM 32612T).

The Polymorphism in ADORA3 Decreases Transcriptional Activity and Influences the Chronic Heart Failure Risk in the Chinese.

AIM: To investigate the genetic contribution of adenosine A3 receptor (ADORA3) gene polymorphisms in the pathogenesis of chronic heart failure (CHF). METHODS: Firstly, a case-control study was performed to investigate the association of ADORA3 polymorphisms with CHF risk. Three hundred northern Chinese Han CHF patients and 400 ethnicity-matched healthy controls were included. Four polymorphisms were genotyped. This case-control study was also replicated in 304 CHF patients and 402 controls from southern China. Finally, the functional variability of positive polymorphism was analyzed using luciferase reporter assay and real-time PCR. RESULTS: Overall, the rs1544223 was significantly associated with CHF risk under the dominant model (P = 0.046, OR = 1.662, 95% CI = 1.009-2.738). But it did not affect disease severity. These results were also consistent in replicated population. In addition, the transcriptional activity for promoter with the A allele was lower than that with the G allele (n = 3, 4.501 ± 0.308 versus 0.571 ± 0.114, P < 0.01) and ADORA3 mRNA levels were significantly higher in GG homozygotes than subjects carrying GA (n = 6, 0.058 ± 0.01 versus 0.143 ± 0.068, P = 0.004) or AA genotypes (n = 6, 0.065 ± 0.01 versus 0.143 ± 0.068, P = 0.008). CONCLUSIONS: Should the findings be validated by further studies with larger patient samples and in different ethnicities, they may provide novel insight into the pathogenesis of CHF.

Effect of hypoglycemic agents on survival outcomes of lung cancer patients with diabetes mellitus: A meta-analysis.

BACKGROUND: To assess the association between hypoglycemic agents and prognosis of lung cancer patients with diabetes. METHODS: A comprehensive literature search was performed in PubMed, Web of Science, Embase, and Cochrane Library until May 2017. The search yielded 2593 unique citations, of which 18 articles met inclusion criteria. The hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated by a fixed-effects or random-effects model. RESULTS: The pooled HRs favoring metformin users were 0.77 for overall survival (OS) (n = 15, 95% CI: 0.68-0.86) and 0.50 for disease-free survival (n = 5, 95% CI: 0.39-0.64). One study assessed the relationship between metformin and cancer-specific survival (CSS), reporting no significant results. No significant association between insulin and OS (n = 2, HR: 0.95, 95% CI: 0.79-1.13) or CSS (n = 2, HR: 1.03, 95% CI: 0.76-1.41) was noted. One study evaluated association of sulfonylureas with lung cancer survival and reported no clinical benefit (HR: 1.10, 95% CI: 0.87-1.40). One study reported no association of thiazolidinediones with lung cancer survival (HR: 1.04, 95% CI: 0.65-1.66). CONCLUSIONS: This meta-analysis demonstrated that metformin exposure might improve survival outcomes in lung cancer patients with diabetes.

Effect of Oridonin on Cytochrome P450 Expression and Activities in HepaRG Cell.

Oridonin, the major terpene found in Rabdosia rubescens, is widely used as a dietary supplement or therapeutic drug. However, the effects of oridonin on major CYP450s are still unclear. As oridonin can enhance the effect of other clinical drugs, in this study, we investigated the influence of oridonin on CYP450s mRNA expression and its impact on activities in human HepaRG cell to evaluate the safety by studying its potential drug interaction. HepaRG cells were cultured with series concentrations of oridonin (1, 5, 10, and 20 µmol/L), and the major CYP450s mRNA and protein expression, as well as enzyme activities were analyzed by real-time polymerase chain reaction, Western blot analysis and UPLC-MS/MS-based metabolite assay. In general, ordonin has induced effects on the major member of CYP450s mRNA and protein expression, as well as on the enzyme activity in human HepaRG cells, especially on CYP3A4 and CYP2C9. To our knowledge, this is the first systematic research about the inductive effects of oridonin on the major member of CYP450s in human cell line. These results may provide at least partly of the basis for potential drug-drug interactions and oridonin should be used with caution to avoid potential risk.

Phenylarsine oxide (PAO) induces apoptosis in HepG2 cells via ROS-mediated mitochondria and ER-stress dependent signaling pathways.

Arsenic trioxide (As2O3) is an old drug that has recently been reintroduced as a therapeutic agent for acute promyelocytic leukemia (APL). Although As2O3 is also applied to treat other types of cancer in vitro and in vivo, it has been reported that single agent As2O3 has poor efficacy against non-hematologic malignant cancers in clinical trials. Recently, a few reports have indicated that organic arsenic compounds can be a possible alternative for the treatment of As2O3-resistant cancers. In this study, we aimed to investigate whether the organic arsenic compound phenylarsine oxide (PAO) has potent cytotoxic effects against human hepatocellular carcinoma (HCC) HepG2 cells. Our results showed that PAO not only had a potent inhibitory effect on the proliferation of HepG2 cells but also activated apoptosis-related proteins (e.g., caspase-3 and -9 and poly-ADP ribose polymerase) in a dose- and time-dependent manner. Furthermore, intracellular ROS were specifically accumulated in the mitochondria and endoplasmic reticulum (ER) after exposure to PAO, implying that they are the target organelles for PAO-induced cytotoxicity. Additionally, when the cells were pretreated with antioxidant N-acetylcysteine (NAC), apoptosis and ER-stress were attenuated significantly, suggesting that induction of apoptosis and cell death probably occurs through the ROS-mediated mitochondria and ER-stress dependent signaling pathways.

Histone deacetylase inhibitor reverses multidrug resistance by attenuating the nucleophosmin level through PI3K/Akt pathway in breast cancer.

The development of multidrug resistance (MDR) is the major obstacle in the chemotherapy of breast cancer, and it restricts the application of antitumor drugs in the clinic. Therefore it is urgent to search for ways to reverse MDR and restore sensitivity to chemotherapeutics in breast carcinoma. Currently, histone deacetylase inhibitors (HDACIs) offer a promising strategy for tumor therapy as the effective anticancer drugs. Based on the potential resistant target of nucleophosmin (NPM), the purpose of this study was to explore the reversal effect of a new synthetic histone deacetylase inhibitor, FA17, on MDR in methotrexate-resistant breast cancer cells (MCF-7/MTX) and xenograft tumors. It was shown that the abnormal expression of NPM induced MDR and inhibited downstream mitochondrial apoptotic pathway by activating PI3K/Akt signaling pathway in MCF-7/MTX cells. The reversal effect and molecular mechanism of FA17 were investigated both in vitro and in vivo. We found that FA17 could significantly reverse resistance and sensitize MCF-7/MTX cells to methotrexate. FA17 obviously enhanced resistant cell apoptosis, inhibited expressions of NPM and efflux transporters. Additionally, FA17 could reverse MDR via inactivating PI3K/Akt pathway and accelerating mitochondrial apoptotic pathway both in MCF-7/MTX cells and in xenograft tumors. Taken together, the novel histone deacetylase inhibitor could effectively reverse drug resistance due to suppressing the activity of NPM and drug efflux pumps by PI3K/Akt and mitochondrial apoptotic pathway. The above not only indicated the potential applied value of FA17 in reversing MDR and enhancing the sensitivity of chemotherapy, but also confirmed the role of NPM in the development of MDR in breast cancer.

The association of ADORA2A and ADORA2B polymorphisms with the risk and severity of chronic heart failure: a case-control study of a northern Chinese population.

The causes of chronic heart failure (CHF) and its progression are likely to be due to complex genetic factors. Adenosine receptors A2A and A2B (ADORA2A and ADORA2B, respectively) play an important role in cardio-protection. Therefore, polymorphisms in the genes encoding those receptors may affect the risk and severity of CHF. This study was a case-control comparative investigation of 300 northern Chinese Han CHF patients and 400 ethnicity-matched healthy controls. Four common single-nucleotide polymorphisms (SNPs) of ADORA2A (rs2236625, rs2236624, rs4822489, and rs5751876) and one SNP of ADORA2B (rs7208480) were genotyped and an association between SNPs and clinical outcomes was evaluated. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the association. The rs4822489 was significantly associated with the severity of CHF after adjustment for traditional cardiovascular risk factors (p = 0.040, OR = 1.912, 95% CI = 1.029-3.550). However, the five SNPs as well as the haplotypes were not found to be associated with CHF susceptibility. The findings of this study suggest that rs4822489 may contribute to the severity of CHF in the northern Chinese. However, further studies performed in larger populations and aimed at better defining the role of this gene are required.

Synthesis of organic nitrates of luteolin as a novel class of potent aldose reductase inhibitors.

Aldose reductase (AR) plays an important role in the design of drugs that prevent and treat diabetic complications. Aldose reductase inhibitors (ARIs) have received significant attentions as potent therapeutic drugs. Based on combination principles, three series of luteolin derivatives were synthesised and evaluated for their AR inhibitory activity and nitric oxide (NO)-releasing capacity in vitro. Eighteen compounds were found to be potent ARIs with IC50 values ranging from (0.099±0.008) µM to (2.833±0.102) µM. O(7)-Nitrooxyethyl-O(3'),O(4')-ethylidene luteolin (La1) showed the most potent AR inhibitory activity [IC50=(0.099±0.008) µM]. All organic nitrate derivatives released low concentrations of NO in the presence of l-cysteine. Structure-activity relationship studies suggested that introduction of an NO donor, protection of the catechol structure, and the ether chain of a 2-carbon spacer as a coupling chain on the luteolin scaffold all help increase the AR inhibitory activity of the resulting compound. This class of NO-donor luteolin derivatives as efficient ARIs offer a new concept for the development and design of new drug for preventive and therapeutic drugs for diabetic complications.

Andrographolide exerted its antimicrobial effects by upregulation of human ß-defensin-2 induced through p38 MAPK and NF-κB pathway in human lung epithelial cells.

Andrographis paniculata (Burm. f) Nees is a traditional herbal medicine for the treatment of infection and inflammation in China. Andrographolide (andro) is one of the major components. Human ß-defensin-2 (hBD-2) is an inducible antimicrobial peptide that plays an important role in innate immunity. The present study aimed to investigate the effect of andro on upregulation of hBD-2 and the key signaling pathways involved in andro-induced hBD-2 expression. Real-time reverse transcription - PCR and Western blot assays showed that andro (1.0-10 µmol/L) can upregulate the expression of hBD-2 in a dose-dependent manner. Further studies suggested that hBD-2 mRNA and protein expression in responsive to andro were attenuated by pretreatment with SB203580 (an inhibitor of p38 mitogen-activated protein kinase (p38 MAPK)), MG-132 (an inhibitor of nuclear factor κB (NF-κB)), and an NF-κB activator inhibitor, but not by an inhibitor of ERK (PD98059) or by an inhibitor of JNK(SP600125). Moreover, we found that a second p38 MAPK inhibitor (SB202190) significantly blocked andro-mediated hBD-2 induction in SPC-A-1 lung epithelial cells. Finally, the p-c-Jun transcription factor activity assay also showed that AP-1 activity was induced by andro compared with the untreated group. We conclude that andro may exert its antimicrobial effects by upregulating the expression of hBD-2 through the p38 MAPK and NF-κB pathway.

Inhibitory effects of ß,ß-dimethylacrylshikonin on hepatocellular carcinoma in vitro and in vivo.

ß,ß-Dimethylacrylshikonin is one of the most abundant naphthoquinones in the root extracts of Lithospermum erythrorhizon Sieb. et Zucc. (Boraginaceae), which have been reported to have antitumor effects. This study evaluated the antiproliferative activity of ß,ß-dimethylacrylshikonin on human hepatocellular carcinoma (HCC) cells both in vitro and in vivo. In vitro, the MTT assay showed that ß,ß-dimethylacrylshikonin inhibited the proliferation of SMMC-7721 cells in both dose- and time-dependent manners with its 50% inhibitory concentration (IC(50) ) at 48 h being 15.01 ± 0.76 µg/mL. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) and Hoechst staining detected the characteristics of cell apoptosis in ß,ß-dimethylacrylshikonin-treated cells and the apoptotic rates of treated groups were increased in a dose-dependent manner. Flow cytometric analysis revealed that ß,ß-dimethylacrylshikonin could block the cell cycle arrest at G2 phase. Furthermore, ß,ß-dimethylacrylshikonin down-regulated the mRNA and protein expression of Bcl-2 but up-regulated that of Bax. The cleaved caspase-3 protein was also detected in treated cells. The experiment in vivo showed that ß,ß-dimethylacrylshikonin significantly suppressed the growth of H(22) transplantable hepatoma, and induced the activation of caspase-3 determined by immunohistochemistry. The results indicate that ß,ß-dimethylacrylshikonin has significant antitumor effects on hepatocellular carcinoma both in vitro and in vivo.

The effect of hypoxia-inducible factor 1-alpha on hypoxia-induced apoptosis in primary neonatal rat ventricular myocytes.

AIM: To study the role of hypoxia-inducible factor 1-alpha (HIF-1alpha) on hypoxia-induced apoptosis in primary neonatal rat ventricular myocytes. METHODS: Primary neonatal rat ventricular myocytes were exposed to hypoxia for 24 hours. HIF-1alpha activity was suppressed by treating the cells with 3-(5'-hydroxymethyl-2'- furyl)-1-benzyl indazole (YC-1). The degree of cell apoptosis was assessed by Hoechst 33258 DNA staining. The levels of HIF-1alpha and the pro-apoptotic proteins Bnip3, Bax and Bad were measured with western blotting. RESULTS: On exposure to hypoxia, there was an increase in the expression levels of HIF-1alpha, and the pro-apoptotic protein Bnip3 was upregulated. Suppression of HIF-1alpha activity by YC-1 treatment was followed by blockade of hypoxia-induced apoptosis and Bnip3 expression; however, the changes in the levels of Bax and Bad expression were unclear. CONCLUSION: Acute hypoxia enhanced primary neonatal rat ventricular myocyte apoptosis through the activation of HIF-1alpha and a mechanism that perhaps involved Bnip3. Targeting HIF-1alpha may be a new strategy for reducing the degree of hypoxia-induced apoptosis in ventricular myocytes.