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  • 1
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. We have identified a neuronal nitric oxide synthase (NOS)-like constitutive form of NOS in vascular smooth muscle (VSM) using a functional contractility approach as well as immunohistochemical methods.2. NG-Nitro-L-arginine methyl ester, NG-monomethyl-L- arginine and NG-nitro-L-arginine (L-NOARG), the competitive inhibitors of NOS, inhibited Mg2+-induced relaxation of de-endothelialized rat aorta precontracted with phenylephrine (PE). This Mg2+ relaxation of VSM was not affected by inhibitors of inducible NOS.3. Electrical field stimulation (EFS; 30–70 Hz) caused relaxation of rat aorta in the presence of tetrodotoxin (therefore not a neurogenic effect) and this EFS relaxation was effectively inhibited by L-NOARG, oxyhemoglobin and methylene blue.4. Immunohistochemical studies of dog saphenous vein using antibodies raised against neuronal NOS indicated prominent staining along the plasmalemma in a punctate pattern similar to the distribution of antibodies against caveolin-1, a major constituent of the plasmalemmal caveolae.5. We propose that a constitutive NOS of non-endothelial, non-neuronal origin is present in a special caveolae domain of VSM cell membranes and could be activated by an ionic mechanism yet to be characterized.
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  • 2
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Fluorescent Ca2+ indicators, such as fura-2/AM and calcium green-1, have become one of the most popular tools for measuring intracellular calcium ([Ca2+]i).2. Electrical stimulation triggers a cascade of events in the cardiac muscle, which results in a [Ca2+]i transient and, eventually, contraction. The events that occur in electrically induced cardiac myocytes mimic the normal physiological events in vivo.3. The electrically induced [Ca2+]i transient represents influx of Ca2+ from outside and mobilization of Ca2+ from the intracellular store and is directly related to contraction. Thus, it is more important to determine the electrically induced [Ca2+]i transient than [Ca2+]i. The [Ca2+]i transient can be easily measured with the spectrofluorescence method using fura 2/AM as the Ca2+ indicator in a single ventricular myocyte preparation.4. We made use of the results of studies on carbachol, tetrandrine and cardiotoxin to illustrate the usefulness of the electrically induced [Ca2+]i transient in the study of actions of cardiac drugs.
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  • 3
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. These studies describe the functional effects of modulation of the sarcoplasmic reticulum (SR) Ca2+ stores at three levels of the vasculature: (i) large arteries (rat and guinea-pig aorta); (ii) small resistance arteries (rat tail artery, rabbit mesenteric artery, dog mesenteric artery); and (iii) arterioles (guinea-pig submucosal arterioles of the small intestine).2. All tissues responded to phenylephrine (PE; 10 μmol/L) with a transient contraction in Ca2+-free Krebs', reflecting Ca2+ release from PE-sensitive Ca2+ stores. After pretreatment with cyclopiazonic acid (CPA; 30 μmol/L) or thapsigargin (TSG; 1 μmol/L), putative SR Ca2+ pump inhibitors, the PE-induced contraction in a Ca2+-free medium was significantly inhibited in arterial tissues at all levels of the vasculature. Similarly, ryanodine (RYA; 30 μmol/L), an agonist that enhances Ca2+ release from the SR, also reduced the PE contraction in a Ca2+-free solution.3. CPA or TSG alone in the presence of extracellular Ca2+, caused marked and sustained contraction in the rat and guinea-pig aorta and marked but transient or no contraction in the resistance arteries. In the rat and guinea-pig aorta, RYA caused a slowly developing tension. Little increase in basal tension was produced by RYA in resistance arteries and arterioles.4. The findings show that an agonist-releasable Ca2+ pool is present at all levels of the vasculature that is independent of the size of the vessels and suggest that under normal physiological conditions there is an intimate balance between the roles of the plasma membrane and of the SR in the maintenance of vascular contractility. It appears that the role of the SR diminishes as the arteries become smaller, while Ca2+ fluxes across the plasma membrane predominates.
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  • 4
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The cytotoxic effects of cardiotoxin (CTX) purified from Cobra venom were tested in endothelium-denuded rat aortic ring preparations in tissue organ baths and the effect of extracellular Ca2+ on the cytotoxic effect of CTX was investigated using a digital dynamic calcium imaging technique.2. At 10 µmol/L, CTX induced a slowly developing and sustained contraction that amounted to approximately 50% of the maximal contraction induced by 80 mmol/L KCl. At high concentrations (〉 15 µmol/L), CTX caused irreversible damage to the smooth muscle contractile function. However, washout of CTX at its peak contraction did not affect the subsequent contraction to either KCl or phenylephrine.3. Contraction induced by CTX was dependent on the Ca2+concentration in the external solution. A maximal contractile response to CTX was obtained in medium containing 1–2.5 mmol/L Ca2+. This contractile response induced by CTX decreased with higher Ca2+ concentrations and was completely diminished when 7 mmol/L Ca2+, 3 mmol/L Ni2+ or 30 µmol/L tetrandrine (a non-selective calcium channel blocker) was present in the external solution before addition of CTX to the bath.4. The above observations were supported by the calcium imaging work performed with cultured aortic smooth muscle cells from Wistar-Kyoto rats, in which CTX was shown to induce the elevation of cytosolic Ca2+ in the presence, but not in the absence, of 2.5 mmol/L extracellular Ca2+. Increasing the extracellular Ca2+ concentration to 7 mmol/L, the addition of 3 mmol/L Ni2+ or inclusion of 30 µmol/L tetrandrine inhibited the elevation of cytosolic Ca2+ induced by CTX.5. These results suggest that: (i) a CTX-sensitive internal calcium store does not exist in rat aortic smooth muscle; (ii) the contractile effect CTX is associated with a Ca2+ influx process; and (iii) CTX interacts extracellularly with the plasma membrane at the level of the calcium channels, as well as anionic sites to which Ca2+ and other inorganic cations bind.
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  • 5
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Symposium PapersCardiovascular protection by ginsenosides and their nitric oxide releasing action X ChenProbing excitation-contraction coupling in trachealis smooth muscle with the mycotoxin cyclopiazonic acid D Amoako, Y Quian, C-Y Kwan and J-P BourreauAntihypertensive effects of DL-tetrahydropalmatine: An active principle isolated from Corydalis MT Lin, FY Chueh, MT Hsieh and CF ChenA family of novel actin-inhibiting marine toxins S-Y Saito and H KarakiIn vitro inhibitory effects of chebulinic acid on the contractile responses of cardiovascular muscles Y-Y Guan, C-Y Kwan, F-L Hsu and J-T ChengTetrandrine as a calcium antagonist H Takemura, K Imoto, H Ohshika and C- Y Kwan
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