摘要:

The vasoconstrictor effects of 9,11-epithio-11,12-methano-thromboxane A2(STA2) on smooth muscle strips of the rabbit coronary artery have been investigated in vitro. Right coronary artery (RCA) was more responsive to STA2than either the left anterior descending or the circumflex coronary artery. On endothelium-denuded RCA strips, the sensitivity and responsiveness to STA2were greater than observed on intact muscle strips. A thromboxane(Tx)-antagonist, (9,11), (11,12)-dideoxa-9a, 11α-dimethylmethano-11,12-methano-13,14-dihydro-13-aza-14-oxo-15-cyclopenthyl-16,17,18,19,20-pethanoI-15-epi-TxA2(ONO-3708), inhibited the STA2-induced contraction, whereas atropine or prazosin had no effect. Nifedipine partly inhibited the STA2-induced contraction, one half of which was still evoked in Ca2+-free solution. When acetylcholine was applied prior to the application of STA2in Ca2+-free solution, the STA2-vasoconstriction disappeared. In saponin-treated chemically skinned muscle strips, STA2itself had no effect on either the pCa-tension relation or on the release of Ca2+from intracellular stores. However, inositol 1,4,5-trisphosphate released Ca2+from such stores, and 12-o-tetradecanoyl phorbol-13-acetate (TPA) and 1,2-diolein, activators of protein kinase C, enhanced the contraction induced by 0.3 μM Ca2+. It is concluded that STA2acts on the TxA2receptor and produces contraction due to an increase in both voltage- and agonist(receptor)-dependent Ca2+influx. STA2also releases Ca2+from ACh- and caffeine-sensitive storage sites.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Contractile agonists can mobilize Ca2+from both intracellular and extracellular stores in smooth muscle. This study addresses the role of Ca2+mobilization as it relates to the complex manner by which Ca2+regulates the contractile system in smooth muscle. In swine carotid media, both histamine and phenylephrine produced initial rapid increases in myosin phosphorylation and stress. Stress was sustained for the duration of the stimulus while myosin phosphorylation slowly declined to steady-state levels. Removal of extracellular Ca2+or elimination of cellular Ca2+influx did not dramatically reduce the initial rapid increase in myosin phosphorylation produced by either agonist but reduced steady-state levels of myosin phosphorylation to basal values. Initial rapid increases in stress were seen, but stress was not maintained. Following depletion of Ca2+from sarcoplasmic reticulum, muscle activation by Ca2+influx in the presence of phenylephrine occurred without an initial transient in myosin phosphorylation, and stress developed slowly. Steady-state levels of myosin phosphorylation and stress were not different from control values. Similar results were obtained with histamine, although a small transient in myosin phosphorylation was also seen. These results are consistent with the hypothesis that the role of the sarcoplasmic reticulum in vascular smooth muscle is to provide high myoplasmic Ca2+concentrations causing extensive myosin phosphorylation and rapid crossbridge cycling leading to rapid stress development. In the presence of extracellular Ca2+, control levels of agonist-induced steady-state stress and myosin phosphorylation could be produced without an initial phosphorylation transient when intracellular Ca2+pools were depleted, suggesting that the sarcoplas mic reticulum is not required for the regulation of steady-state myoplasmic [Ca2+] during “latch.”

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Cultured bovine aortic endothelial cells (BAEC) contain renin and angiotensinogen. To examine whether angiotensins are synthesized intracellularly and secreted by these cells, we assayed cell extracts as well as serum-free media of intact confluent BAEC. Angiotensins were identified by their retention time on reverse phase high performance liquid chromatography and direct radioimmunoas-say. BAEC and their media contain angiotensin II and angiotensin III. The rate of angiotensin accumulation in the media was a nonlinear function of time; the highest rate occurred in the first 15 minutes. The amount of angiotensin II accumulated in 30 minutes exceeded 200% of the intracellular concentration and that of angiotensin III exceeded 500% of the initial intracellular content. Neither renin nor angiotensinogen could be detected in the media. The viability of these cells was supported by low lactic dehydrogenase activity in the media (<0.5% of cellular level). These data suggest that BAEC is capable of synthesizing and secreting angiotensins. We postulate tht this endothelial-derived angiotensin system may play an important paracrine or autocrine role in influencing local vascular tone.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The present series of experiments used gas chromatography to identify vapor-phase photoproducts liberated during exciter laser irradiation of cardiovascular tissues in air and blood. In air, laser beams produced from ArF (193 nm) and XeF (351 nm) exciter laser gas mixtures were delivered to samples of myocardium and atherosclerotic coronary arterial segments through the wall of a quartz cell, using 8–40 mj/pulse. In blood, 351 nm were delivered via an optical fiber, using 14 mj/pulse. When the experiments were performed using an air-tissue interface, the dominant photoproducts identified in order of elution from the gas chromatographic column were methane, acetylene, ethyl-ene, ethane, propyne, allene, propylene, propane, and butene. When a fiberoptic was used to accom plish 351-nm excimer laser tissue ablation in a blood field, a similar gas chromatographic spectral distribution was observed. These vapor-phase photoproducts are indistinguishable from those ob served following continuous wave laser irradiation or flame torching of cardiovascular tissues. Thus, despite the fact that excimer laser ablation of cardiovascular tissues is characterized by the absence of signs of thermal injury, the results of these experiments suggest that the predominant mechanism of excimer ablation is, like continuous-wave laser irradiation, a thermal process.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The kinetics of crossbridge phosphorylation and cellular activation rates in arterial smooth muscle are unknown, and the response rates are usually limited by agonist diffusion rates. In this study, electrical field stimulation (10–20 V AC, 60 Hz) was used to activate strips of swine carotid artery smooth muscle. Pretreatment with 0.5 μM phenoxybenzamine (PBZ) for 30 minutes significantly inhibited field stimulated stress due to nor epinephrine released from adrenergic nerves. Addition of 1–10 mM tetraethyl ammonium ion (TEA) to PBZ-pretreated tissues allowed direct stimulation of muscle cells and significantly potentate the response to field stimulation. Activation in field stimulated tissues pretreated with PBZ and TEA was strongly inhibited by the Ca2+-channel antagonist verapamil (0.5 μM for 15 minutes). Activation was rapid with myosin light chain (MLC)-phosphorylation values rising to greater than 50% of total MLC, with a half-time of approximately 1 second. Stress and stiffness development was biphasic and lagged with an estimated half-time for the first phase of 3 seconds. Stress and stiffness continued to slowly rise after 5 seconds of stimulation, while MLC phosphorylation declined significantly between 5 and 10 seconds to a nearly constant value of 35–40% for up to 60 seconds. Unloaded shortening velocity was maximal (0.067 L0/sec) at the earliest time point examined (0.5 second), prior to significant stress development and at submaximal phosphoryla tion. Significant decreases in unloaded shortening velocity were observed after 10 seconds. These results show that the kinetics of phosphorylation and dephosphorylation and the rates of activation are very rapid in this arterial smooth muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The instantaneous force-velocity relations of cat papillary muscles were studied at different times in the twitch in normal and in postextrasystolic potentiated contractions. Fourteen to sixteen different loads were used to define each of the force-velocity curves. The curves were fitted by a least-squares procedure to the hyperbolic (Hill equation). The hyperbolae were extrapolated to obtain maximum velocity and isometric force and interpolated to obtain maximum power. All three of these values rose more quickly than developed force. Maximum velocity reached 77% of its peak at the earliest time studied, 20–25% of the time to peak force. Developed force achieved 22% of its final value at this time, while extrapolated isometric force and maximum power both reached 44% of their peak values. Postextrasystolic potentiation sufficient to produce a 1.5 to twofold increase in peak developed force produced less than a 20% increase in extrapolated maximum velocity. The results can be interpreted in terms of a model in which the maximum velocity of the contractile elements remains constant during the twitch. Variation in maximum velocity is attributed to a small internal load, equivalent to 6% of twitch force. Since maximum velocity is relatively constant, it does not give a good measure of changes in the force-velocity curves. By contrast, the extrapolated isometric force and maximum power are much more sensitive to changes in the force-velocity curves, and they vary in proportion to each other. The advantage of using interpolated maximum power rather than isometric force to define changes in the curves is that it can be normalized to muscle mass.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

To determine the feasibility of quantitative ultrasonic techniques to define the composition of athero sclerotic plaques, samples of freshly excised human aortas were sewn to a sample holder and immersed in a saline bath for ultrasonic interrogation. Integrated backscatter of a 2-microsecond portion of the backscattered radiofrequency signal was measured with a 10 MHz focused transducer. Integrated backscatter was calculated by normalizing the root-mean-square voltage of the gated signal to the root-mean-square voltage obtained by replacing the tissue sample with a nearly perfect reflector. Microscopic examination of the 124 interrogated sites allowed differentiation of normal, fibrous, fibrofatty, and calcified regions. A site was considered calcified if it contained any histochemically detectable calcium. Values of integrated backscatter were markedly elevated from calcified regions (−30.0 ± 6.4 dB, n = 25; mean ± SD; p< 0.001) compared to normal (−43.2 ± 2.4 dB, n = 20) and fibrofatty (− 43.9 ± 3.4 dB, n = 43) sites. Values from fibrous regions (− 40.7 ± 3.8 dB, n = 36) were also significantly different compared with the calcified and fibrofatty regions (p<0.001). Thus, we have demonstrated that quantitative ultrasonic backscatter identifies and differentiates calcification and fibrosis in atherosclerotic sites offering promise for the noninvasive assessment of the pathologic status of the arterial wall.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID