舒尼替尼对结肠成纤维细胞体内外抑制机制研究(英文)

研究目的:探索小分子酪氨酸激酶抑制剂舒尼替尼(sunitinib)对结肠肿瘤微环境中的肿瘤相关成纤维细胞的作用及其机制。创新要点:舒尼替尼通过抑制肿瘤间质成纤维细胞的生长,间接发挥抗肿瘤效应,为结肠癌综合治疗的提供新途径。研究方法:通过细胞周期分析和细胞增殖测定进行舒尼替尼体外抑制肿瘤细胞的研究。采用Western-blot检测磷酸化血小板衍生生长因子β受体(PDGFR-β)、蛋白激酶B(Akt)及细胞外信号调节蛋白激酶(ERK)的蛋白水平。通过注射肠腺癌细胞株SW620和结肠成纤维细胞构建的裸鼠移植瘤模型来研究舒尼替尼的体内抑瘤效果。重要结论:舒尼替尼可有效抑制结肠癌来源的原代结肠成纤维细胞生长,该抑制作用主要通过抑制血小板衍生生长因子(PDGF)信号通路得以实现。     

Chlorogenic acid prevents acetaminophen-induced liver injury: the involvement of CYP450 metabolic enzymes and some antioxidant signals

Chlorogenic acid (CGA), a polyphenolic compound, is abundant in fruits, dietary vegetables, and some medicinal herbs. This study investigated the prevention of CGA against acetaminophen (AP)-induced hepatotoxicity and its engaged mechanisms. CGA reversed the decreased cell viability induced by AP in L-02 cells in vitro. In addition, CGA reduced the AP-induced increased serum levels of alanine/aspartate aminotransferase (ALT/AST) in vivo. The effect of CGA on cytochrome P450 (CYP) enzymatic (CYP2E1, CYP1A2, and CYP3A4) activities showed that CGA caused very little inhibition on CYP2E1 and CYP1A2 enzymatic activities, but not CYP3A4. The measurement of liver malondialdehyde (MDA), reactive oxygen species (ROS), and glutathione (GSH) levels showed that CGA prevented AP-induced liver oxidative stress injury. Further, CGA increased the AP-induced decreased mRNA expression of peroxiredoxin (Prx) 1, 2, 3, 5, 6, epoxide hydrolase (Ephx) 2, and polymerase (RNA) II (DNA directed) polypeptide K (Polr2k), and nuclear factor erythroid-2-related factor 2 (Nrf2). In summary, CGA ameliorates the AP-induced liver injury probably by slightly inhibiting CYP2E1 and CYP1A2 enzymatic properties. In addition, cellular important antioxidant signals such as Prx1, 2, 3, 5, 6, Ephx2, Polr2k, and Nrf2 also contributed to the protection of CGA against AP-induced oxidative stress injury.     

Influence of low protein diets on gene expression of digestive enzymes and hormone secretion in the gastrointestinal tract of young weaned piglets

To investigate dietary protein level effects on digestive mechanisms, weaned piglets were fed for 45 d with diets containing 20%, 17%, or 14% crude protein (CP) supplemented to meet requirements for essential amino acids. This article describes the influence of dietary protein on gastrointestinal hormones and expression of an array of digestive enzymes in the gastrointestinal tract and pancreas. Results indicated that there were no significant differences in expression of enzymes involved in carbohydrate digestion, except for maltase in the duodenum. In the jejunum, amylase expression in pigs fed 20% CP was much higher than that in pigs fed other diets (P<0.05) and maltase expression in those fed 17% CP was higher than that in other treatments (P<0.05). Although there were no remarkable differences in expression of aminopeptidase in the small intestine or carboxypeptidase in the pancreas (P>0.05), there was a trend towards higher expression of various proteases in pigs fed 17% CP. The duodenal expression of enteropeptidase in diets with 14% and 17% CP was significantly higher than that with 20% CP (P<0.05), but treatment differences did not existed in jejunum (P>0.05). The expression of GPR93 as a nutrient-responsive G protein-coupled receptor in 14% and 17% CP diets was significantly higher than that in 20% CP diet in the small intestine (P<0.05). The expressions of genes for pancreatic enzymes, lipase and elastase, were significantly higher in pigs fed diets with low CP, while similar trends occurred for carboxypeptidase, chymotrypsin and amylase. Conversely, the gastric expressions of pepsinogen A and progastricsin were lower with the 17% CP diet. Differences between treatments were found in the gastric antral contents of cholecystokinin and somatostatin: both increased in pigs fed 17% CP, accompanied by decreased content of motilin, which was also seen in plasma concentrations. These patterns were not reflected in duodenal contents. In general, 17% dietary CP was beneficial to the digestion of nutrient substance in the gastrointestinal tract.     

A simple and inexpensive enteric-coated capsule for delivery of acid-labile macromolecules to the small intestine

Understanding the ecology of the gastrointestinal tract and the impact of the contents on the host mucosa is emerging as an important area for defining both wellness and susceptibility to disease. Targeted delivery of drugs to treat specific small intestinal disorders such as small bowel bacterial overgrowth and targeting molecules to interrogate or to deliver vaccines to the remote regions of the small intestine has proven difficult. There is an unmet need for methodologies to release probes/drugs to remote regions of the gastrointestinal tract in furthering our understanding of gut health and pathogenesis. In order to address this concern, we need to know how the regional delivery of a surrogate labeled test compound is handled and in turn, if delivered locally as a liquid or powder, the dynamics of its subsequent handling and metabolism. In the studies we report on in this paper, we chose ¹³C sodium acetate (¹³C-acetate), which is a stable isotope probe that once absorbed in the small intestine can be readily measured non-invasively by collection and analysis of ¹³CO₂ in the breath. This would provide information of gastric emptying rates and an indication of the site of release and absorptive capacity. In a series of in vitro and in vivo pig experiments, we assessed the enteric-protective properties of a commercially available polymer EUDRAGIT®L100-55 on gelatin capsules and also on DRcaps®. Test results demonstrated that DRcaps®coated with EUDRAGIT®L100-55 possessed enhanced enteric-protective properties, particularly in vivo. These studies add to the body of knowledge regarding gastric emptying in pigs and also begin the process of gathering specifications for the design of a simple and cost-effective enteric-coated capsule for delivery of acid-labile macromolecules to the small intestine.     

CIDE gene expression in adipose tissue,liver, and skeletal muscle from obese and lean pigs

The expression of the cell death-inducing DNA fragmentation factor α-like effector (CIDE) family including Cidea, Cideb, and Cidec was significantly increased in mouse and human models of obesity. However, there was less information on these genes’ expression in pigs. Here, we hypothesized that different fat accumulation between lean (Duroc×Landrace×Yorkshire gilts, DLY) and obese (Lantang) pigs was attributed to porcine CIDE-modulating lipid metabolism. Our data showed that Cidea and Cidec were expressed at a high level in adipose tissue, and at a relatively high level in skeletal muscle, whereas Cideb was mainly expressed in the liver in both breeds of pig. Lantang pigs had higher white adipose and skeletal muscle Cidea and Cidec mRNA abundance, and hepatic and muscle Cideb mRNA than DLY pigs. Lipid metabolism-related genes including sterol regulatory element binding protein 1c (SREBP-1c), hepatocyte nuclear factor-4α (HNF-4α), peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), fatty acid synthase (FASN), diacylglycerol O-acyltransferase 1 (DGAT1), and DGAT2 showed a higher expression level in adipose tissue from obese pigs than in that from lean pigs. Lantang pigs exhibited higher mRNA abundance for liver SREBP-1c, HNF-4α, and PGC-1α, and higher skeletal muscle SREBP-1c, HNF-4α, PGC-1α, and DGAT2 expression, as compared with DLY pigs. However, the perlipin2 mRNA levels in adipose tissues, liver, and skeletal muscle were significantly lower in obese pigs than in their lean counterparts. Furthermore, plasma non-esterified fatty acid (NEFA), glucose, and triacylglycerol (TAG) levels were greater in obese pigs than in lean pigs. Finally, data from correlation analysis further found that CIDE mRNA expression was positively correlated with back fat thickness (BFT), abdominal fat mass (AFM), and the levels of NEFA, TAG, and glucose in the two breeds. Collectively, these data revealed that the porcine CIDEs possibly modulated lipid metabolism and contributed to the development of fat deposition and obesity in Lantang pigs.     

<Emphasis Type="Italic">Phyllanthus emblica</Emphasis> Linn. fruit extract potentiates the anticancer efficacy of mitomycin C and cisplatin and reduces their genotoxicity to normal cells in vitro

Objective

Fruit of Phyllanthus emblica Linn. (PE) is widely consumed as a functional food and used as a folk medicine due to its remarkable nutritional and pharmacological effects. Mitomycin C (MMC) and cisplatin (cDDP) are the most widely used forms of chemotherapeutic drug, but their clinical use is limited by their genotoxicity to normal cells. We aimed to determine whether PE has potential to reduce the genotoxicity, while improving the anticancer effect, of MMC and cDDP.

Methods

Cell proliferation was evaluated using the trypan blue exclusion assay and colony-forming assay. Genomic instability (GIN) was measured using the cytokinesis-block micronucleus assay.

Results

Co-treatment (72 h) with PE at 20–320 μg/ml significantly enhanced the efficacy of MMC (0.05 μg/ml) and cDDP (1 μg/ml) against Colo205 colorectal cancer cells (P<0.05), and at 80–320 μg/ml significantly decreased MMCand cDDP-induced GIN and multinucleation in normal colonic NCM460 cells (P<0.05). PE significantly decreased the mitotic index (P<0.01), blocked mitotic progression (P<0.05), and promoted apoptosis (P<0.01) in MMC- and cDDP-treated NCM460 cells, suggesting that PE-mediated inhibition of mitosis and induction of apoptosis may limit the division and survival of highly damaged cells. Also, PE was found to inhibit the clonal expansion of MMC- and cDDP-treated NCM460 cells (P<0.05) and decrease the heterogeneity of the surviving clones.

Conclusions

PE potentiates the anticancer efficacy of MMC and cDDP, while preventing their genotoxicity and inhibiting clonal expansions of unstable genomes in normal cells. These data suggest that PE has the potential to reduce the risk of secondary cancers induced by chemotherapeutics.

     

Effect of interrupted endogenous BMP/Smad signaling on growth and steroidogenesis of porcine granulosa cells

Bone morphogenetic proteins (BMPs) play a critical role in the growth and steroidogenesis of granulosa cells (GCs). BMP signals act through membrane-bound heteromeric serine/threonine kinase receptors. Upon ligand binding, BMPs activate intracellular Smad proteins and regulate growth and apoptosis in various cell types. The objective of this study was to demonstrate the effects of BMP/Smad signal on growth and steroidogenesis of porcine GCs. A strategy of RNA interference (RNAi)-mediated ‘gene silencing’ of Smad4, a core molecule mediating the intracellular BMP/Smad signal transduction pathways, was used to interrupt endogenous BMP/Smad signaling. Results indicate that Smad4-small interfering RNA (siRNA) caused specific inhibition of Smad4 mRNA and protein expression after transfection. Interrupted endogenous BMP/Smad signaling significantly inhibited growth, and induced apoptosis of porcine GCs, while decreasing estradiol production. In addition, interrupted BMP/Smad signaling significantly (P<0.05) changed the expression of Cyclin D2, CDK4, Bcl-2, and Cyp19a1. These findings provide new insights into how BMP/Smad signaling regulates the growth and steroidogenesis of porcine GCs.     

Cytotoxicity and effect of extraction methods on the chemical composition of essential oils of Moringa oleifera seeds

Renewed interest in natural materials as food flavors and preservatives has led to the search for suitable essential oils. Moringa oleifera seed essential oil was extracted by solvent-free microwave and hydrodistillation. This study assessed its chemical constituents. Cytotoxicity of the oils was investigated using hatchability and lethality tests on brine shrimps. A total of 16 and 26 compounds were isolated from the hydrodistillation extraction (HDE) and solvent-free microwave extraction (SME) oils, respectively, which accounted for 97.515% and 97.816% of total identifiable constituents, respectively. At 24 h when the most eggs had hatched, values of the SME (56.7%) and HDE (60.0%) oils were significantly different (P<0.05) from those of sea water (63.3%) and chloramphenicol (15.0%). Larva lethality was different significantly (P<0.05) between HDE and SME oils at different concentrations and incubation periods. The median lethal concentration (LC₅₀) of the oils was >1000 mg/ml recommended as an index for non-toxicity, which gives the oil advantage over some antioxidant, antimicrobial, therapeutic, and preservative chemicals.     

Effect of siRNA-mediated knockdown of eIF3c gene on survival of colon cancer cells

Eukaryotic initiation factor subunit c(eIF3c) has been identified as an oncogene that is over-expressed in tumor cells and,therefore,is a potential therapeutic target for gene-based cancer treatment.This study was focused on investigating the effect of small interfering RNA(siRNA)-mediated eIF3c gene knockdown on colon cancer cell survival.The eIF3c gene was observed to be highly expressed in colon cancer cell models.The expression levels of the gene in eIF3c siRNA infected and control siRNA infected cells were compared via real-time polymerase chain reaction(PCR) and western blotting analysis.Cell proliferation levels were analyzed employing 3-(4,5-dimethylthiazol 2-yl)-2,5-diphenyltetrazolium bromide(MTT) and colony formation assays.Furthermore,the effects of eIF3c gene knockdown on the cell cycle and apoptosis were analyzed using flow cytometry.The results showed that suppression of eIF3c expression significantly(P<0.001) reduced cell proliferation and colony formation of RKO colon cancer cells.The cell cycle was arrested by decreasing the number of cells entering S phase.Further,apoptosis was induced as a result of eIF3c knockdown.Collectively,eIF3c deletion effectively reduced the survival of colon cancer cells and could be used as a therapeutic tool for colon cancer therapy.     

顺铂联合热处理对术中回收血红细胞及其中混杂的肝肿瘤细胞株(HepG2)的影响（英文）

目的:研究离体热处理和顺铂联合热处理对术中回收血红细胞功能的影响及其中混杂的肝肿瘤细胞株(HepG2)的杀灭作用。创新点:(1)采用多种评价指标研究了不同时间离体热处理对术中回收血中混杂的HepG2的杀灭作用及对红细胞的影响,并确定了对红细胞安全且能有效杀灭HepG2的离体热处理时间。(2)从多个角度评价了离体顺铂联合热处理对术中回收血红细胞的影响及对其中混杂的HepG2的杀灭作用,确定了该方案中对红细胞安全且能有效去除HepG2的顺铂浓度。方法:采用3-(4,5-二甲基噻唑-2)-2,5-二苯基四氮唑溴盐(MTT)、5-乙炔基-2’脱氧尿嘧啶核苷(EdU)和平板克隆形成评估HepG2的细胞存活率、DNA复制率和克隆形成能力(图1和3);从红细胞渗透脆性、携氧能力(2,3-二磷酸甘油酸(2,3-DPG)、半饱和氧分压(P50))、能量代谢(Na+-K+-ATPase、pH)、膜完整性(游离血红蛋白(Hb)、血清K+和Na+浓度、细胞膜磷脂酰丝氨酸外翻比例)等角度评估红细胞功能(图2和4;表3)。结论:肝肿瘤术中回收血经离体顺铂联合热处理(42°C,50μg/ml)60min后,能有效清除其中混杂的HepG2,但对红细胞无显著影响,值得体内进一步研究顺铂热处理有效应用于肿瘤手术自体血液回输的安全方案。     

A high-fat diet increases body fat mass and up-regulates expression of genes related to adipogenesis and inflammation in a genetically lean pig

Because of their physiological similarity to humans, pigs provide an excellent model for the study of obesity. This study evaluated diet-induced adiposity in genetically lean pigs and found that body weight and energy intake did not differ between controls and pigs fed the high-fat (HF) diet for three months. However, fat mass percentage, adipocyte size, concentrations of total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), insulin, and leptin in plasma were significantly higher in HF pigs than in controls. The HF diet increased the expression in backfat tissue of genes responsible for cholesterol synthesis such as Insig-1 and Insig-2. Lipid metabolism-related genes including sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase 1 (FASN1), diacylglycerol O-acyltransferase 2 (DGAT2), and fatty acid binding protein 4 (FABP4) were significantly up-regulated in backfat tissue, while the expression of proliferator-activated receptor-α (PPAR-α) and carnitine palmitoyl transferase 2 (CPT2), both involved in fatty acid oxidation, was reduced. In liver tissue, HF feeding significantly elevated the expression of SREBP-1c, FASN1, DGAT2, and hepatocyte nuclear factor-4α (HNF-4α) mRNAs. Microarray analysis further showed that the HF diet had a significant effect on the expression of 576 genes. Among these, 108 genes were related to 21 pathways, with 20 genes involved in adiposity deposition and 26 related to immune response. Our results suggest that an HF diet can induce genetically lean pigs into obesity with body fat mass expansion and adipose-related inflammation.     

Effects of hypoxic exercise training on microRNA expression and lipid metabolism in obese rat livers

To investigate the effects of hypoxic exercise training on microRNA (miRNA) expression and the role of miRNA expression in regulating lipid metabolism, 20 dietary-induced obese SD rats were divided into a normoxic sedentary group (N, n=10) and a hypoxic exercise training group (H, n=10). After four weeks, measurements were taken of body weight, body length, fat mass, serum lipid concentration, miRNAs differentially expressed in rat liver, and gene and protein expression levels of peroxisome proliferator activated receptor α (PPARα), fatty acid synthetase (FAS), and carnitine palmitoyl transferase 1A (CPT1A) in rat liver. Body weight, Lee’s index, fat mass, fat/weight ratio, and serum levels of total cholesterol (TC) and high density lipoprotein cholesterol (HDL-C) were all significantly lower in the H group than in the N group (P<0.01). Six miRNAs expressed significantly differently in the liver (P<0.05). Specifically, expression levels of miR-378b were significantly lower in the H group than in the N group (P<0.05). Compared with the normoxic sedentary group, hypoxic exercise training resulted in a lower ratio of FAS mRNA to CPT1A mRNA (P<0.05), as well as lower CPT1A protein levels (P<0.01), while a higher ratio of FAS to CPT1A protein levels (P<0.01) was observed. In conclusion, hypoxic training may elevate the resistance of high fat diet induced obesity in rats by reducing the expression of miR-378b, and decrease the fatty acid mitochondrial oxidation in obese rat livers by decreasing the protein expression of CPT1A and increasing the protein expression ratio of FAS/CPT1A.     

Alteration of <Emphasis Type="Italic">SlYABBY2b</Emphasis> gene expression impairs tomato ovary locule number and endogenous gibberellin content

Tomato is an ideal model species for fleshy fruit development research. SlYABBY2b regulates the ovary locule number, which is increased by gibberellins, in tomato. However, the relationship between SlYABBY2b and endogenous gibberellin is poorly understood. In this study, SlYABBY2b-overexpressing and RNA interference (RNAi) transgenic tomato plants were used to elucidate the mechanism by which SlYABBY2b regulates the ovary locule number and endogenous gibberellin content in tomato. SlYABBY2b-overexpressing plants showed fewer locules and lower gibberellin content than the control plants. Contrasting results were found in the RNAi lines. Therefore, the SlYABBY2b gene negatively regulates tomato ovary locule number and endogenous gibberellin content. Furthermore, the expression of SlYABBY2b gene was remarkably higher than that of the wild type in the apical shoots of gibberellindeficient mutants. This showed that the gibberellins can inhibit the expression of SlYABBY2b gene negative regulation. Further study revealed that SlYABBY2b suppressed the expression of SlGA20ox1 and SlGA3ox2, but increased that of SlGA2ox1 and SlGA2ox5 in the apical shoots of SlYABBY2b-overexpressing plants, thereby reducing gibberellin content. Contrasting results were found in the RNAi lines. Our results showed that the SlYABBY2b gene was located on gibberellin signal transduction pathways, fed back regulation of the synthesis of gibberellin, and felt exogenous gibberellin signal to further regulate the formation of tomato locule.     

Rumen fermentation and acetogen population changes in response to an exogenous acetogen TWA4 strain and Saccharomyces cerevisiae fermentation product

The presence of yeast cells could stimulate hydrogen utilization of acetogens and enhance acetogenesis. To understand the roles of acetogens in rumen fermentation, an in vitro rumen fermentation experiment was conducted with addition of acetogen strain (TWA4) and/or Saccharomyces cerevisiae fermentation product (XP). A 2×2 factorial design with two levels of TWA4 (0 or 2×10⁷ cells/ml) and XP (0 or 2 g/L) was performed. Volatile fatty acids (VFAs) were increased (P<0.05) in XP and TWA4XP, while methane was increased only in TWA4XP (P<0.05). The increase rate of microorganisms with formyltetrahydrofolate synthetase, especially acetogens, was higher than that of methanogens under all treatments. Lachnospiraceae was predominant in all acetogen communities, but without close acetyl-CoA synthase (ACS) amino acid sequences from cultured isolates. Low-Acetitomaculum ruminis-like ACS was predominant in all acetogen communities, while four unique phylotypes in XP treatment were all amino acid identified low-Eubacterium limosum-like acetogens. It differs to XP treatment that more low-A. ruminis-like and less low-E. limosum-like sequences were identified in TWA4 and TWA4XP treatments. Enhancing acetogenesis by supplementation with an acetogen strain and/or yeast cells may be an approach to mitigate methane, by targeting proper acetogens such as uncultured low-E. limosum-like acetogens.     

Effects of dietary fresh fermented soybean meal on growth performance,ammonia and particulate matter emissions,and nitrogen excretion in nursery piglets

This study was conducted to investigate the effects of fresh fermented soybean meal (FSM) on the growth performance of nursery piglets, nitrogen excretion in feces, and the concentrations of ammonia (NH₃) and particulate matter (PM) in the piggery. A total of 472 nursery piglets (Landrace×Yorkshire, (16.3±0.36) kg body weight) were randomly allocated into two treatments with 236 pigs in each treatment. The pigs were fed the basal diet without fresh FSM (control) or diet containing 10% (100 g/kg) fresh FSM (FSM group), and the crude protein content of the two groups was consistent. The feeding trial lasted for 28 d. The results showed that the pigs fed fresh FSM had increased (P<0.05) average daily gain (ADG) compared with the control. There was no significant difference (P>0.05) in feed to gain ratio (F:G) between the two groups. During the whole experiment, the concentration of NH₃ in the piggery decreased (P<0.05) by 19.0%, and the concentrations of PM (PM₁₀ and PM_2.5) in the piggery decreased (P<0.05) by 19.9% and 11.6%, respectively, in the FSM group, compared with the control. The ammonia nitrogen and nitrite content in feces increased (P<0.05) by 32.9% and 28.4%, respectively, in the FSM group. The fecal pH declined (P<0.05) significantly in the FSM group compared with the control. At the end of experiment, total protein (TP) concentration was increased (P<0.05) significantly and blood urea nitrogen (BUN) concentration was decreased (P<0.05) for pigs fed the diet with fresh FSM. The results indicated that dietary fresh FSM not only improved the growth performance of nursery piglets, but also reduced the NH₃ concentration in the piggery due to nitrogen conversion, and decreased the concentrations of PM₁₀ and PM_2.5 in the piggery.     

Reduction of methylviologen-mediated oxidative stress tolerance in antisense transgenic tobacco seedlings through restricted expression of StAPX

Ascorbate peroxidases are directly involved in reactive oxygen species (ROS) scavenging by reducing hydrogen peroxide to water. The tomato thylakoid-bound ascorbate peroxidase gene (StAPX) was introduced into tobacco. RNA gel blot analysis confirmed that StAPX in tomato leaves was induced by methylviologen-mediated oxidative stress. The sense transgenic seedlings exhibited higher tAPX activity than that of the wild type (WT) plants under oxidative stress conditions, while the antisense seedlings exhibited lower tAPX activity. Lower APX activities of antisense transgenic seedlings caused higher malondialdehyde contents and relative electrical conductivity. The sense transgenic seedlings with higher tAPX activity maintained higher chlorophyll content and showed the importance of tAPX in maintaining the optimal chloroplast development under methylviologen stress conditions, whereas the antisense lines maintained lower chlorophyll content than WT seedlings. Results indicated that the over-expression of StAPX enhanced tolerance to methylviologen-mediated oxidative stress in sense transgenic tobacco early seedlings, whereas the suppression of StAPX in antisense transgenic seedlings showed high sensitivity to oxidative stress.     

Streptomycin inhibits electrophysiological changes induced by stretching of chronically infarcted rat hearts

Objective

To investigate stretch-induced electrophysiological changes in chronically infarcted hearts and the effect of streptomycin (SM) on these changes in vivo.

Methods

Sixty Wistar rats were divided randomly into four groups: a control group (n=15), an SM group (n=15), a myocardial infarction (MI) group (n=15), and an MI+SM group (n=15). Chronic MI was obtained by ligating the left anterior descending branch (LAD) of rat hearts for eight weeks. The in vivo blockade of stretch-activated ion channels (SACs) was achieved by intramuscular injection of SM (180 mg/(kg·d)) for seven days after operation. The hearts were stretched for 5 s by occlusion of the aortic arch. Suction electrodes were placed on the anterior wall of left ventricle to record the monophasic action potential (MAP). The effect of stretching was examined by assessing the 90% monophasic action potential duration (MAPD₉₀), premature ventricular beats (PVBs), and ventricular tachycardia (VT).

Results

The MAPD₉₀ decreased during stretching in both the control (from (50.27±5.61) ms to (46.27±4.51) ms, P<0.05) and MI groups (from (65.47±6.38) ms to (57.47±5.76 ms), P<0.01). SM inhibited the decrease in MAPD₉₀ during inflation ((46.27±4.51) ms vs. (49.53±3.52) ms, P<0.05 in normal hearts; (57.47±5.76) ms vs. (61.87±5.33) ms, P<0.05 in MI hearts). The occurrence of PVBs and VT in the MI group increased compared with that in the control group (PVB: 7.93±1.66 vs. 1.80±0.86, P<0.01; VT: 7 vs. 1, P<0.05). SM decreased the occurrence of PVBs in both normal and MI hearts (0.93±0.59 vs. 1.80±0.86 in normal hearts, P<0.05; 5.40±1.18 vs. 7.93±1.66 in MI hearts, P<0.01).

Conclusions

Stretch-induced MAPD₉₀ changes and arrhythmias were observed in chronically infarcted myocardium. The use of SM in vivo decreased the incidence of PVBs but not of VT. This suggests that SACs may be involved in mechanoelectric feedback (MEF), but that there might be other mechanisms involved in causing VT in chronic MI.