垂体后叶素和加压素对离体心肌的直接作用

本实验采用大鼠离体右心房和右心室肌条模型,观察了垂体后叶素和加压素对右心房和右心室肌的直接作用。结果表明:垂体后叶素对右心房的自主性收缩频率和幅度及右心室肌的收缩幅度均有剂量依赖性抑制作用;加压素对右心房和右心室肌收缩幅度也有剂量依赖性抑制作用,但对右心房自主节律无影响;催产素对右心房的收缩频率和幅度则均无影响。加压素V_1、V_2受体拮抗剂d(CH_2)_5Tyr(Me)AVP和d(CH_2)_5(D-Ile~2,Ile~4,Ala(NH_2)~9)AVP对垂体后叶素的负性变力作用具有不同程度的阻断作用,但对垂体后叶素的负性变时作用无阻断作用。以上结果提示,垂体后叶素的负性变力作用主要是由加压素产生的,加压素对心肌有直接的负性变力作用;垂体后叶素的负性变时作用可能是非加压素和催产素成分的作用结果。     

Purified moniliformin does not affect the force or rate of contraction of isolated guinea pig atria

Aspergillus flavus Link ex Fries and A. parasiticus Speare can invade peanut kernels and under certain environmental conditions produce unacceptable levels of the mycotoxin aflatoxin. A concerted effort is underway to reduce aflatoxin contamination in peanut and peanut products. A potentially effective method of control in peanut is the discovery and use of genes for resistance to either fungal invasion or aflatoxin formation. The objective of the present experimental study was to develop an effective and efficient procedure for screening individual plants or pods of single plants for resistance to invasion by the aflatoxigenic fungi and subsequent aflatoxin production. Methods of obtaining adequate drought-stress and fungal infection were developed through this series of experiments. By completely isolating the pods from the root zone and imposing drought-stress only on pegs and pods, high levels of fungal infection were observed. High amounts of preharvest aflatoxin accumulation were also produced by completely isolating the pods from the root zone. Mid-bloom inoculation with A. parasiticus-contaminated cracked corn and drought-stress periods of 40 to 60 days were the most effective procedures. This technique was used to assess peanut genotypes previously identified as being partially resistant to A. parasiticus infection or aflatoxin contamination, and segregating populations from four crosses. Variability in aflatoxin contamination was found among the 11 genotypes evaluated, however, none were significantly lower than the standard cultivars. Broad-sense heritability of four crosses was estimated through evaluation of seed from individual plants in the F₂ generation. The heritability estimates of crosses GFA-2 × NC-V11 and Tifton-8 × NC-V11 were 0.46 and 0.29, respectively, but mean aflatoxin contamination levels were high (73,295 and 27,305 ppb). This greenhouse screening method could be an effective tool when genes for superior aflatoxin resistance are identified.Cooperative investigation of the USDA-ARS and the University of Georgia, College of Agriculture.     

Influence of sarmesin on the cardiac and vascular actions of angiotensin II

Summary The angiotensin II (ANG II) receptor blocker properties of sarmesin and its influence on the homotropic cooperativity of ANG II receptors were studied in two experimental models: isolated rabbit aorta and isolated rabbit atria. The results show that: (i) sarmesin is a specific competitive antagonist of ANG II receptors, with high affinity (pA₂=8.93 in the isolated aorta and 8.66 in the isolated atria); and (ii) the slope of the concentration-response curves to ANG II and the Hill coefficient increased in the presence of sarmesin, the latter suggesting an enhancement of the positive homotropic cooperativity of ANG II receptors. These results may be explained overall by the reciprocal negative modulation of receptor affinity between sarmesin and ANG II, due, possibly, to opposite effects on the binding of G-proteins to ANG II receptors.     

Cytosolic and nuclear calcium signaling in atrial myocytes: IP3-mediated calcium release and the role of mitochondria

In rabbit atrial myocytes Ca signaling has unique features due to the lack of transverse (t) tubules, the spatial arrangement of mitochondria and the contribution of inositol-1,4,5-trisphosphate (IP₃) receptor-induced Ca release (IICR). During excitation-contraction coupling action potential-induced elevation of cytosolic [Ca] originates in the cell periphery from Ca released from the junctional sarcoplasmic reticulum (j-SR) and then propagates by Ca-induced Ca release from non-junctional (nj-) SR toward the cell center. The subsarcolemmal region between j-SR and the first array of nj-SR Ca release sites is devoid of mitochondria which results in a rapid propagation of activation through this domain, whereas the subsequent propagation through the nj-SR network occurs at a velocity typical for a propagating Ca wave. Inhibition of mitochondrial Ca uptake with the Ca uniporter blocker Ru360 accelerates propagation and increases the amplitude of Ca transients (CaTs) originating from nj-SR. Elevation of cytosolic IP₃ levels by rapid photolysis of caged IP₃ has profound effects on the magnitude of subcellular CaTs with increased Ca release from nj-SR and enhanced CaTs in the nuclear compartment. IP₃ uncaging restricted to the nucleus elicites ‘mini’-Ca waves that remain confined to this compartment. Elementary IICR events (Ca puffs) preferentially originate in the nucleus in close physical association with membrane structures of the nuclear envelope and the nucleoplasmic reticulum. The data suggest that in atrial myocytes the nucleus is an autonomous Ca signaling domain where Ca dynamics are primarily governed by IICR.     

Correlation between endogenous polyamines in human cardiac tissues and clinical parameters in patients with heart failure

Polyamines contribute to several physiological and pathological processes, including cardiac hypertrophy in experimental animals. This involves an increase in ornithine decarboxylase (ODC) activity and intracellular polyamines associated with cyclic adenosine monophosphate (cAMP) increases. The aim of the study was to establish the role of these in the human heart in living patients. For this, polyamines (by high performance liquid chromatography) and the activity of ODC and N¹‐acetylpolyamine oxidases (APAO) were determined in the right atrial appendage of 17 patients undergoing extracorporeal circulation to correlate with clinical parameters. There existed enzymatic activity associated with the homeostasis of polyamines. Left atria size was positively associated with ODC (r = 0.661, P = 0.027) and negatively with APAO‐N¹‐acetylspermine (r = −0.769, P = 0.026), suggesting that increased levels of polyamines are associated with left atrial hemodynamic overload. Left ventricular ejection fraction (LVEF) and heart rate were positively associated with spermidine (r = 0.690, P = 0.003; r = 0.590, P = 0.021) and negatively with N¹‐acetylspermidine (r = −0.554, P = 0.032; r = −0.644, P = 0.018). LVEF was negatively correlated with cAMP levels (r = −0.835, P = 0.001) and with cAMP/ODC (r = −0.794, P = 0.011), cAMP/spermidine (r = −0.813, P = 0.001) and cAMP/spermine (r = −0.747, P = 0.003) ratios. Abnormal LVEF patients showed decreased ODC activity and spermidine, and increased N¹‐acetylspermidine, and cAMP. Spermine decreased in congestive heart failure patients. The trace amine isoamylamine negatively correlated with septal wall thickness (r = −0.634, P = 0.008) and was increased in cardiac heart failure. The results indicated that modifications in polyamine homeostasis might be associated with cardiac function and remodelling. Increased cAMP might have a deleterious effect on function. Further studies should confirm these findings and the involvement of polyamines in different stages of heart failure.     

Do ATP and UTP involve cGMP in positive inotropism on rat atria?

ATP and UTP induced a dual inotropic effect in rat left atria: first a decrease and then an increase in contractile tension were observed. PPADS, an antagonist of P2X receptors, inhibited positive inotropism induced by ATP and alpha,beta-meATP. Chiefly, we investigated intracellular mechanisms responsible for the positive inotropism. We tested cromakalim and glibenclamide, an activator and an inhibitor, respectively, of ATP-sensitive K(+) channels. These compounds did not influence the effects of ATP. IBMX, a phosphodiesterase inhibitor, and H-7, an inhibitor of protein kinase C and cAMP-dependent protein kinase, did not modify the inotropic effects of ATP. Instead, H-8, an inhibitor of cAMP- and cGMP-dependent protein kinases, strongly inhibited the positive effects of both ATP and UTP, suggesting the possible involvement of cGMP in the inotropism. Also, LY 83583, an inhibitor of cGMP production, reduced positive inotropism by alpha,beta-meATP, ATP and UTP. Moreover, 8-Br-cGMP (50 microM), a stable analogue of cGMP, inhibited positive inotropism by all nucleotides. Lastly, we determined intracellular cGMP levels by RIA; the cyclic nucleotide increased during positive inotropism induced by ATP and UTP. The results regarding positive inotropism suggest that: (a) ATP acts through P2X receptors, while UTP may act by P2X, but also through PPADS-insensitive receptors; and (b) changes in intracellular cGMP concentration are involved in this inotropic effect.     

The in vitro chronotropic and inotropic effects of vasoactive intestinal peptide (VIP) on the atria and ventricular papillary muscle from Cynomolgus monkey heart

The in vitro chronotropic and inotropic effects of vasoactive intestinal peptide (VIP) and of isoproterenol, two agents known to stimulate cardiac adenylate cyclase were compared on the heart from Cynomolgus monkey using the spontaneously beating right atrium, the electrically stimulated left atrium, and the electrically-stimulated ventricular papillary muscle. VIP increased concentration-dependently the rate of beating of the right atrium as well as the contractility of both atria but its efficiency was lower than that of D,L-isoproterenol. VIP also stimulated concentration-dependently, and this time as efficiently as D,L-isoproterenol, the contractility of papillary muscle. These VIP effects were unaltered by the neuronal blocker tetrodotoxin. In addition, the moderate inhibition exerted by the beta-adrenergic blocker D,L-propranolol on VIP effects argued against the implication of beta-adrenergic receptors in VIP effects. These results indicate that VIP exerts a direct stimulatory influence on the rate and contractility of Cynomolgus monkey heart.     

Role of cardiovascular nitric oxide system in C-type natriuretic peptide effects

The aims were to evaluate the role of cardiovascular nitric oxide (NO)-system in C-type natriuretic peptide (CNP) actions and to investigate receptor types and signaling pathways involved in this interaction. Wistar rats were infused with saline or CNP. Mean arterial pressure (MAP) and nitrites and nitrates (NOx) excretion were determined. NO synthase (NOS) activity and NOS expression (Western blot) were analyzed in atria, ventricle and aorta. CNP decreased MAP and increased NOx excretion. CNP estimulated NOS activity, inducing no changes on cardiac and vascular endothelial NOS expression. NOS activity induced by CNP was abolished by suramin and calmidazoliumand but it is not modified by anantin. CNP would interact with NPR-C receptor coupled via G proteins leading to the activation Ca(2+)-calmodulin dependent endothelial NOS, increasing NO production which would induce the reduction in cardiac myocyte contractility and ANP synthesis and secretion in right atria and the relaxation of vascular smooth muscle.     

Circulating antibodies against neonatal cardiac muscarinic acetylcholine receptor in patients with Sjögren's syndrome

Isolated congenital heart block may be associated with Primary Sjogren's Syndrome. In this work we demonstrated that IgG present in the sera ofpatients with Primary Sjogren's Syndrome (PSS) could bind and activate muscarinic acetylcholine receptors of rat neonatal atria. These antibodies were able to inhibit in a irreversible manner the binding of ³H-QNB to muscarinic cholinergic receptors of purified rat atria membranes. Moreover, IgG from PSS individuals could modify biological effects mediated by muscarinic cholinoceptors activation, i.e. decrease contractility and cAMP and increase phosphoinositide turnover and cGMP. Atropine blocked all of these effects and carbachol mimicked them; confirming muscarinic cholinergic receptors-mediated PSS IgG action. Neither binding nor biological effect were obtained using adult instead of neonatal rat atria. IgG from sera of normal women were not effective in the studied system. The prevalence of cholinergic antibody was 100% in PSS and was independent of Ro/SS-A and La/SS-B antibodies. It could be concluded that antibody against muscarinic cholinergic receptors may be another serum factor to be considered in the pathophysiology of the development of congenital heart block.     

豚鼠心房存在苯环立啶受体

用氚标记苯环立啶([~3H]-pcp)与豚鼠心房匀浆蛋白作受体结合试验。结果表明豚鼠心房具有与[~3H]-PCP 相结合的部位,结合具有特异性、饱和性、可逆性和立体专一性。Scatchard 分析,豚鼠心房有两个不同亲和力的特异结合部位;高亲和力和低亲和力结合部位。两者的解离常数 K_(dl)和K_(d2)分别为12.15±0.414nmol/L 和561.23±121.36nmol/L,最大结合 B_maxl 为0.71±0.029 pmol/mg 蛋白,B_maxe 为1.047±0.099 pmol/mg 蛋白。竞争性抑制分析结果显示 PCP 受体和 sigma 受体的配基都可抑制[~3H]-PCP 的结合,PCP 受体的配基的抑制作用强于 sigma 配基,而广谱阿片激动剂埃托啡(etorphine)却无抑制作用。结果提示豚鼠心房存在 PCP 受体。豚鼠右心房的冰冻切片和[~3H]-PCP 进行体外受体结合放射自显影,结果显示,在心房肌层有与[~3H]-PCP 特异性结合部位,且呈比较均匀的散在分布。