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M Masuo

Publications and source records attributed to M Masuo.

15 recordsLinked to original sources
PubMed1992

Myosin light chain phosphatase activities and the effects of phosphatase inhibitors in tonic and phasic smooth muscle.

Phosphatase inhibitors microcystin-LR, tautomycin, and okadaic acid caused contraction and increased 20-kDa myosin light chain (MLC20) phosphorylation in Ca(2+)-free solutions in both phasic and tonic smooth muscle permeabilized with beta-escin, and inhibited the heavy meromyosin (HMM) phosphatase activity of smooth muscle homogenates with the same potency sequence: microcystin-LR greater than tautomycin greater than okadaic acid. The sensitivity to all three inhibitors was significantly higher, the half-times of relaxation and dephosphorylation were 4-6 times longer, and the HMM phosphatase and MLC20 kinase activity/smooth muscle cell wet weight was 2.0- and 1.9-fold lower in the tonic, femoral artery, than in the phasic, ileum or portal vein, smooth muscle. Preincubation with 0.2 microM inhibitor-2 decreased the HMM phosphatase activity by 35% in the ileum and by 60% in the femoral artery. The results suggest that the HMM phosphatases of smooth muscle have properties common to type 1 protein phosphatases, but are inhibited only partially by high concentrations of inhibitor-2, and that the lower HMM phosphatase activity of tonic smooth muscle may contribute to its greater sensitivity to phosphatase inhibitors and its slower rate of relaxation.

Animals↗
PubMed1992

Mechanism of inhibitory effects of azelastine on smooth muscle contraction.

The mechanism of inhibitory effects of azelastine, an antiallergic and antiasthmatic agent, on depolarization- and alpha-1 adrenergic agonist-induced contractions of intact smooth muscle was studied. The effects of azelastine on membrane currents were determined in isolated guinea pig ileum smooth muscle cells with the whole-cell clamp technique; the effects on contraction were evaluated in receptor- and G-protein-coupled, alpha-toxin-permeabilized rabbit femoral artery and portal vein smooth muscle strips. Azelastine (1-20 microM), like dihydropyridines, inhibited spontaneous rhythmic and high K(+)-induced contractions, mainly through inhibition of the voltage-dependent (L-type) Ca++ current. The tonic component of high K+ contractions was inhibited more than the phasic component, correlating to voltage-dependent inhibition of Ca++ current by the drug. Azelastine (IC50 of 0.25 microM), a known histamine blocker, also reversibly inhibited alpha-1 agonist-induced contractions in the presence and absence of extracellular Ca++. Both major pathways of pharmacomechanical coupling, agonist-induced Ca++ release from the sarcoplasmic reticulum and Ca++ sensitization of the regulatory/contractile apparatus were blocked by the same concentration of drug in permeabilized as in intact muscle. Inositol 1,4,5-trisphosphate-induced Ca++ release and guanosine 5'-O-(tau-thiotriphosphate)-induced Ca++ sensitization, however, were not inhibited. Azelastine at high (greater than 10 microM) concentrations reversibly inhibited Ca(++)-activated contraction, more potently at lower Ca++ concentration and in phasic smooth muscle, but inhibited neither adenosine 5'-O-(tau-thiotriphosphate)-induced, Ca(++)-independent nor phorbol ester-induced contractions. These results indicate that azelastine is a genuine Ca++ antagonist that inhibits voltage-gated Ca++ inward current and agonist-induced Ca++ release and Ca++ sensitization.

Animals↗
PubMed1991

G protein-mediated inhibition of myosin light-chain phosphatase in vascular smooth muscle.

The mechanism of G protein-mediated sensitization of the contractile apparatus of smooth muscle to Ca2+ was studied in receptor-coupled alpha-toxin-permeabilized rabbit portal vein smooth muscle. To test the hypothesis that Ca2+ sensitization is due to inhibition of myosin light-chain (MLC) phosphatase activity, we measured the effect of guanosine 5'-[gamma-thio]triphosphate and phenylephrine on the rate of MLC dephosphorylation in muscles preactivated with Ca2+ and incubated in Ca(2+)- and ATP-free solution containing 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) to block MLC kinase activity. Guanosine 5'-[gamma-thio]triphosphate alone (300 microM) or in combination (3 microM) with phenylephrine decreased the rates of relaxation and dephosphorylation of MLC to about half of control values; this inhibition is sufficient to account for maximal G protein-mediated Ca2+ sensitization of MLC phosphorylation. The rate of thiophosphorylation of MLC with adenosine 5'-[gamma-thio]-triphosphate was not affected by guanosine 5'-[gamma-thio]triphosphate. We suggest that inhibition of protein phosphatase(s) by G protein(s) may have important regulatory functions.

Adenosine Triphosphate↗
PubMed1991

Subpopulations of rat vascular smooth muscle cells as discriminated by calcium release mechanisms from internal stores.

Transsarcolemmal influx and release from the sarcoplasmic reticulum (SR) through specific Ca2+ channels are the two main pathways to elevate cytosolic Ca2+ (Ca2+i) in vascular smooth muscle cells (VSMCs). To elucidate intercellular distribution and function of the Ca2+ channel in SR in cultured VSMCs, we observed Ca2+i transients by digital two-dimensional imaging with a fluorescent Ca2+ indicator, fura-2, and found an alternative response to either caffeine or angiotensin II under the condition that selectively enabled Ca2+ release from SR. Caffeine (20 mM) increased the Ca2+i by 292 +/- 36% (mean +/- SEM) over the basal level in one third of the VSMC population (n = 19), while the remaining cells in the same observation field showed no or very weak response (110 +/- 4%). In contrast, after the treatment with caffeine plus ryanodine (30 microM), which inactivates the caffeine-sensitive channel, and with 1 mM Ca2+ chelator (EGTA) instead of Ca2+ in the incubation medium to block the CA2+ entry from outside, angiotensin II (10 nM) induced the Ca2+i elevation (287 +/- 26%) in previously caffeine-nonresponsive cells, although caffeine-responsive cells retained quiescence (112 +/- 2%). These responses did not differ when the order of the reagent application was reversed. These heterogeneities of VSMCs in the Ca2+i response to vasoactive substances indicate that VSMCs are functionally divided into subgroups with different Ca2+ channel predominance on SR, necessitating reevaluation of the previous studies obtained from multiple VSMCs.

Angiotensin II↗
PubMed1991

Growth-dependent alterations of intracellular Ca(2+)-handling mechanisms of vascular smooth muscle cells. PDGF negatively regulates functional expression of voltage-dependent, IP3-mediated, and CA(2+)-induced Ca2+ release channels.

To examine the alterations of intracellular Ca2+ ([Ca2+]i)-handling mechanisms in cultured vascular smooth muscle cells (VSMCs) of rat aorta (Shin et al Circ Res 1991;69:551-556), we stimulated VSMCs by extracellular high K+, caffeine, and angiotensin II and evaluated Ca2+ influx through voltage-dependent Ca2+ channels, Ca(2+)-induced Ca2+ release, and inositol trisphosphate-dependent Ca2+ release from internal stores. Percentage of VSMCs responding to each stimulant (responder ratio) and degree of [Ca2+]i increase in the responding cells were analyzed by a two-dimensional fura-2 imaging system. The responder ratios to the three stimulants were high (70-90%) in the quiescent phase (days 1-2), although some cells selectively responded to one or two of the stimulants. Responder ratios prominently decreased to approximately 20% in the proliferating phase (days 2.5-3). In the subconfluent (days 3.5-4) and postconfluent (days 5-6) phases, the responder ratio to high K+ and angiotensin II recovered to the same level as during the quiescent phase, whereas that to caffeine remained low (approximately 10-20%). In responding cells, the degree of [Ca2+]i increase by caffeine and angiotensin II was stable (approximately 100%) during culturing, whereas that to high K+ was small (approximately 30-40%) in the quiescent and proliferating phases and rapidly increased threefold in the subconfluent and postconfluent phases. Furthermore, arrest of cell growth in serum-free medium prevented the reduction of responder ratios in the proliferating phase and restored the decreased ratio of the caffeine responder. Acceleration of VSMC proliferation by platelet-derived growth factor decreased the ratios in all phases. These results imply that 1) the functional expressions of [Ca2+]i-handling mechanisms in response to these vasoactive stimuli are influenced by cell growth and cytodifferentiation of VSMCs or platelet-derived growth factor and 2) they are regulated independently from each other.

Angiotensin II↗
PubMed1991

Noninvasive method to obtain input function for measuring tissue glucose utilization of thoracic and abdominal organs.

We have developed a method for the noninvasive estimation of regional tissue glucose utilization in humans that employs positron emission tomography (PET) and 2-(18F)fluoro-2-deoxy-d-glucose (FDG). Unlike other methods, the input function used in this method is obtained from the corrected time-activity curve of the descending aorta, not the left ventricle, because the descending aorta is relatively free of spillover from other organs and extends from the upper thorax to the lower abdomen. With this method the time-activity curve of the descending aorta must be corrected for the partial volume effect and the difference in counts between plasma and whole blood. Using the noninvasively obtained input function, regional tissue glucose utilization was calculated by Patlak graphic analysis. k1k3/(k2 + k3) was in good agreement with k1k3/(k2 + k3) calculated from the plasma input function by arterial sampling (r = 0.9995). These results suggest that the input function and regional tissue glucose utilization (not only of myocardium but also of other thoracic and abdominal organs) can be determined noninvasively.

Abdomen↗
PubMed1988

Effects of alpha human atrial natriuretic polypeptide on the systemic hemodynamics and coronary circulation in patients with ischemic heart disease.

Alpha human atrial natriuretic polypeptide (alpha-hANP) was intravenously infused into 7 patients with ischemic heart disease who had almost normal cardiac function at a rate of 0.025 micrograms/kg/min for 15 min. During infusion of alpha-hANP, left ventricular (LV) systolic pressure decreased from 144 +/- 19 (SD) to 129 +/- 22 mmHg (p less than 0.01), LV end diastolic pressure (EDP) from 15 +/- 5 to 13 +/- 4 mmHg (p less than 0.05), mean aortic pressure from 102 +/- 14 to 91 +/- 14 mmHg (p less than 0.01), time constant of LV pressure fall (T) from 100 +/- 15 to 88 +/- 13 msec (p less than 0.05), systemic vascular resistance (SVR) from 1711 +/- 206 to 1424 +/- 340 dynes.sec.cm-5 (p less than 0.05) and coronary vascular resistance (CVR) from 8.5 +/- 1.2 to 7.4 +/- 1.3 x 10(4) dynes.sec.cm-5 (p less than 0.05). There was a linear correlation between percent changes in SVR and those of CVR (r = 0.92, p less than 0.01), and the fall in CVR was approximately 68% of that in SVR. Increases occurred in heart rate from 63 +/- 7 to 66 +/- 8 beats/min (p less than 0.05), LV dp/dt from 1558 +/- 266 to 1627 +/- 238 mmHg/sec (p less than 0.05), LV dp/dt/p from 22.9 +/- 3.2 to 25.6 +/- 3.7/sec (p less than 0.01), and myocardial oxygen consumption (from 7.9 +/- 2.4 to 9.8 +/- 2.1 ml/min, p less than 0.05), while mean right atrial and mean pulmonary arterial pressures and pulmonary vascular resistance were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Experimental canine arterial thrombus formation and thrombolysis: a fiberoptic study.

We produced arterial thrombi that simulated the clinical condition in canine iliac arteries by endothelial denudation and partial occlusion. The processes of thrombus formation and thrombolysis were examined by vascular fiberscope. Laminar mural thrombi developed in all 21 preparations 10 minutes after blood reperfusion, with stenosis formation. Over 50% luminal obstruction with thrombi occurred in 10 preparations 30 minutes after inducing stenosis. Total occlusion with thrombi occurred in four preparation (31%) at 1 hour, and in all nine at 3 hours after inducing stenosis. Usually, red thrombus at the denudated region grew in size distal to the sited of stenosis. Histologically, thrombi of less than 1 hour duration consisted of a loose fibrin network and those of over 3 hours' duration consisted of a dense fibrin network. Infusion of 144,000 IU of urokinase (UK) reduced the size of thrombi less than 1 hour old during fiberoptic observation. However, UK infusion of similar dose failed to recanalize two of four preparations with 3-hour-old thrombi. In conclusion, arterial thrombi that closely simulate those observed clinically can be made by endothelial denudation and partial occlusion, and the vascular fiberscope provides a useful method for analysis of thrombosis and thrombolysis.

Animals↗
PubMed1987

[Effects of alpha-human atrial natriuretic polypeptide (alpha-hANP) on congestive heart failure in dogs].

Effects of alpha-human atrial natriuretic polypeptide (alpha-hANP) on a model of congestive heart failure (CHF), we established in dogs, were investigated. The model was made by protease injection into the left ventricular free wall, saline loading, and dextran and methoxamine infusion. By this maneuver, left atrial pressure (LAP), systemic vascular resistance (SVR) and left ventricular end-diastolic pressure (LVEDP) were markedly increased, aortic blood flow (AoBF) was decreased and systemic blood pressure (SBP) was unchanged. Following intravenous application of 0.50 microgram/kg alpha-hANP, LAP was reduced from 18.9 to 14.0 mmHg (N = 7, mean); SBP, from 114.4 to 105.1 mmHg; SVR, from 21603 to 15602 dyne sec/cm5; and LVEDP, from 22.2 to 17.6 mmHg; while AoBF was increased from 0.46 to 0.54 l/min. Vmax and T were little influenced. The results indicate that alpha-hANP improved canine CHF mainly through its vasodilating action.

Animals↗
PubMed1987

Evaluation of regurgitant fraction of the left ventricle by gated cardiac blood-pool scanning using SPECT.

Regurgitant fraction (RF) of patients with and without mitral regurgitation (MR) and/or aortic regurgitation (AR) was evaluated by gated cardiac blood-pool scanning using single photon emission computed tomography (SPECT). Using the stroke count image of a short-axis tomogram to separate the right atrium and ventricle, the left ventricular stroke count (LVSC) and right ventricular stroke count (RVSC) were determined. The RF equaled (LVSC - RVSC)/LVSC. Calculated RF in 14 subjects without significant regurgitation by contrast angiography was 5.8 +/- 5.9% (mean +/- s.d.), RF of 17 cases with angiographic regurgitation was 42.5 +/- 16.8% (p less than 0.001). The sensitivity of the radionuclide method compared to angiography was 94% (16/17 cases), and specificity was 100% (14/14 cases). RF of mild Re (1+ or 2+) was 26.0 +/- 8.9% (n = 6) and RF of severe Re (3+ or 4+) was 51.5 +/- 12.7% (n = 11) (p less than 0.001). Correlation between the RF determined with the radionuclide method and with cardiac catheterization was good (y = 5.85 + 0.700 x, r = 0.821, n = 17). We conclude that RF of MR and/or AR can be accurately evaluated by gated cardiac blood-pool scanning using SPECT.

Cardiac Catheterization↗
PubMed1986

Fiberoptic observation of thrombosis and thrombolysis in isolated human coronary arteries.

Coronary arteries isolated from cadavers autopsied within 7 hours after death were perfused with canine arterial blood, and the processes of thrombus formation at the segments stenosed with atheroma and the thrombolytic effects of urokinase were investigated by angioscopy. Ten minutes of blood perfusion caused thin mural thrombi localized at the stenotic or nonstenotic segments. During 30 minutes of blood perfusion, the thin mural thrombi of the outlet or inlet of the segment grew into a doughnut-shaped thrombus. Also, the thin mural thrombi in the stenotic segment grew into a streamer-like thrombus and drifted downstream. These thrombi grew in size with increasing perfusion time and finally obstructed the stenotic segment. Globular thrombi close to the outlet also were formed in a few preparations. Unlike the thrombi at the stenotic segment, the mural thrombi in the nonstenotic segments did not grow into massive thrombi. The thrombi were reduced in size within 10 minutes of perfusion with 320 U/ml or more of urokinase. During thrombolysis, sandstorm-like dispersion of the blood cells occurred, small fragments detached from the mother thrombus and flew downstream, or the fibrin core of the thrombus was exposed. The results indicate the usefulness of angioscopy for the dynamic and serial investigation of thrombosis and thrombolysis.

Adult↗
PubMed1986

[Effects of forskolin on canine congestive heart failure].

Forskolin is a diterpene of the labdane family which activates adenylate cyclase. The effects of forskolin were investigated in a congestive heart failure (CHF) model that we newly established using anesthetized dogs. The model was made by the intramural injection of protease into the left ventricular free wall, saline loading, and dextran and methoxamine infusion. By this maneuver, aortic blood flow (AoBF) was decreased; left atrial pressure (LAP), systemic vascular resistance (SVR) and left ventricular endodiastolic pressure (LVEDP) were markedly increased; and systemic blood pressure was unchanged. A bolus injection of 5.0 micrograms/kg forskolin reversed the hemodynamic findings of CHF. It reduced LAP (17.5----7.9 mmHg) (mean, N = 7), SVR (19980----10390 dyne sec/cm5), time constant T (90.7----59.2 msec) and LVEDP (22.8----16.8 mmHg); and it increased Vmax (2.32----2.82 l/sec) and AoBF (0.50----0.72 l/min). Forskolin improved the CHF mainly through its vasodilator and positive inotropic actions.

Animals↗
PubMed1986

A decrease in plasma factor which stimulates prostaglandin I2 synthesis in patients with acute myocardial infarction.

PG I2 stimulating plasma factor was measured in patients with ischemic heart disease and age-matched controls. The plasma factor measured by bioassay using rat aorta was 3.2 +/- 0.6 (n = 21), 2.7 +/- 0.8 (n = 7), 1.6 +/- 1.5*** (n = 18) and 2.2 +/- 0.06** (n = 3) PG I2 ng/mg rat aorta (mean +/- SD; * p less than 0.05, ** p less than 0.01, *** p less than 0.001) in control, angina pectoris, acute myocardial infarction and old myocardial infarction with angina pectoris groups, respectively. The plasma factor measured by radioimmunoassay was 43.5 +/- 19.5 (n = 11), 35.4 +/- 13.1 (n = 4), 38.5 +/- 18.0 (n = 9), 26.0 +/- 20.1* (n = 7) and 59.5 +/- 31.2 (n = 5) ng/mg rat aortic protein/15 min in control, variant angina, stable angina, acute myocardial infarction and old myocardial infarction groups, respectively. The factor in deproteinized plasma of the acute myocardial infarction group was also smaller than that of the control group. PG I2 synthesis by rat aortic ring was inhibited by mepacrine, which inhibits phospholipase A2. The plasma factor was not inactivated by heating. The results indicate that a heat-stable plasma factor which acts on phospholipase A2 or on its surrounding reaction systems is deficient in the early stage of acute myocardial infarction. A decrease in the factor may cause PG I2 deficiency, resulting in coronary thrombosis or vasospasm and consequently in acute myocardial infarction.

Aged↗