摘要:

A prejunctional mechanism involving an α1-adrenergic receptor may exert control on the release of acetylcholine from parasympathetic nerve endings in the heart. To test this hypothesis in vivo, rats were prepared for electrical stimulation of the vagus nerves. Blood pressures and heart rates were monitored, and the animals were treated with α-agonists and α-antagonists. The α1-selective agonist phenylephrine significantly attenuated vagally induced bradycardia in a dose-dependent fashion (ED50= 19 μg/kg). This is consistent with the hypothesis that there is α-adrenergic inhibition of ACh release. In contrast, the α2-selective agonist, BHT-920, caused no change in heart rate during vagal stimulation. The effects of phenylephrine to raise heart rate and blood pressure during vagal stimulation were blocked by the α1-selective antagonist prazosin (ID50approximately 1 μg/kg) but not by the α2-selective antagonists yohimbine and rauwolscine. This further supports an α1assignment to the prejunctional adrenergic receptor mechanism, which can regulate the release of acetylcholine from cardiac parasympathetic neurons.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

31P-NMR has been used extensively to estimate intracellular pH. It also can be used to measure extracellular pH and volume when an NMR-detectable extracellular phosphorous probe is used. Phosphonic acids have been suggested as useful31P-NMR extracellular markers. The present study was designed to assess the utility of phenylphosphonic acid (PPA) as a31P-NMR extracellular marker in perfused smooth muscle. Rabbit bladder strips were exposed to PPA concentrations of 1–20 mM. Tension development in response to maximal carbachol challenges (10 μM) was independent of PPA concentration. Addition of PPA (6 mM) to the perfusate supplying the isolated resting rabbit bladder had no effect on31P-NMR-detectable phosphatic compounds. PPA's resonance frequency was distinctly downfield from endogenous phosphates and demonstrated a pH-dependent chemical shift of ± 1.12 ppm/pH unit over the range of 6.4 to 7.6 with a pK' of 7.09 at 23± C. The time courses for washing PPA in and out of the resting bladder were best described by monotonic exponential growth (r= 0.972;n= 3) and decay (r= 0.972;n= 3) equations, respectively. Rate and time constants for PPA wash-in (0.039 ± 0.004 min−1and 25.7 ± 2.3 minutes) and washout (0.038 ± 0.000 min−1and 26.3 ± 0.0 minutes) were not significantly different. Using steady state PPA and ATP peak intensities and concentrations, an extracellular-to-intracellular ratio was calculated to be 0.31 ± 0.03 (n= 3). These data indicate that PPA remains distributed exclusively in the extracellular spaces. Further, they affirm that PPA is noncytotoxic and pH-sensitive over a physiological pH range under normal flow conditions. Using PPA, therefore, is a reliable way to measure both extracellular pH and volume while concomitantly monitoring the energy state of the cell. These measurements will assist in understanding the dynamic interdependence of extracellular and intracellular metabolic events.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The role of cytoskeletal damage in the disruption of the plasma membrane observed during myocardial ischemia has been studied using antibodies to vinculin to identify changes in the distribution of this membrane associated cytoskeletal protein. Vinculin is a component of the cytoskeletal attachment complex between the plasma membrane and the Z-line of the underlying myofibrils. The effects of varying periods of total ischemia on the localization of vinculin were assessed by immunofluorescence and evidence of membrane disruption was evaluated by electron microscopy. Thin tissue slices prepared from the ischemic tissue were incubated in oxygenated Krebs-Ringer phosphate buffer at 37± C to assess inulin permeability, ultrastructure, and any changes in the distribution of vinculin associated with incubation. The previously reported costameric pattern of vinculin staining was observed in longitudinal sections of control myocardium, myocardium subjected to 60 minutes of total ischemia, and myocardium subjected to 60 minutes of ischemia followed by 60 minutes of incubation in oxygenated media. Electron microscopy and inulin permeability measurements confirmed that plasma membrane integrity was preserved under these conditions. However, when the duration of total ischemia was extended to 120 minutes or longer, there was a progressive loss of vinculin staining along the lateral margin of myocytes. This change correlates with the appearance of subsarcolemmal blebs and breaks in the plasma membranes observed by electron microscopy and confirmed by the increase in inulin permeability observed in tissue slices. These data demonstrate that there is a close association between cytoskeletal damage and plasma membrane disruption and suggest that breakdown of the cytoskeletal scaffold underlying the plasma membrane may be responsible for weakening the plasma membrane and allowing it to rupture as a consequence of cell swelling during ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Hypertrophy of the mammalian heart, regardless of the initiating event, results in architectural remodeling of ventricular components that maintain structural and functional characteristics of this organ. Ventricular components that vary their morphology and morphometry in a hypertrophic state are the muscle cells, connective tissue elements, vasculature, or a combination of some or all of the above. Morphologic quantification of the progressive tissue changes occurring throughout the natural life span of the spontaneously hypertensive and normotensive Wistar-Kyoto rats has not been thoroughly documented. Using perfused-fixed tissue from both strains at 1, 6, 12, 18, and 24 months of age, we have determined the morphometric changes that occurred in the subepicardial and midwall regions of the left ventricle. Myocyte cell size, wall thickness, and arterial blood pressure were elevated in 1-month-old spontaneously hypertensive rats, reached significance by 6 months, and remained significantly greater throughout the 24 months examined. Tissue morphometry demonstrated significant tissue component volumetric differences at 6 months in the spontaneously hypertensive rat. Age-related morphometric tissue changes occurred in both strains yet were exacerbated (percent volume of myocytes) or diminished (percent volume interstitial space) in the mature and aging spontaneously hypertensive rat. Capillary density of SHR left ventricle showed a drastic decline so that 6-month-old SHR had the same density as a senescent Wistar-Kyoto. Tissue morphometry and capillary density data strongly support the hypothesis that tissue oxygenation is diminished in the spontaneously hypertensive rat, and as a result, tissue necrosis and myocyte cell death occur.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

To investigate the mechanisms of action of ryanodine and caffeine, changes in mechanical and electrical activity caused by these agents were correlated with alterations in45Ca fluxes and cell Ca contents in chick embryo ventricular cell monolayer cultures. Ryanodine (10−10-10−5M) irreversibly decreased contraction amplitude by 10–70% relative to control in a concentration-dependent manner with minimal effects on electrical activity. Ryanodine caused a slight decrease in rapid45Ca uptake, but no change in total exchangeable calcium content or rapid45Ca efflux. Caffeine (1-20 mM) caused a transient (less than 10 seconds) 5–12% increase in contraction amplitude followed by a sustained 9–76% decrease in contraction amplitude and a 10 mV decrease in diastolic membrane voltage. Caffeine caused a decrease in rapid45Ca uptake, a decrease in total exchangeable calcium content, and an increase in rapid45Ca efflux. These results suggest that caffeine produces a decrease in sarcoplasmic reticulum (SR) Ca2+uptake, and/or an increase in SR Ca2+release that eventually depletes the SR of Ca2+, presumably accounting for the negative inotropic effect. The ryanodine effects on contraction are more difficult to account for solely in terms of alterations of transsarcolemmal Ca2+fluxes and Ca2+contents. Our data indicate an important role for the SR in excitation-contraction coupling in cultured chick embryo ventricular cells and suggest that SR Ca2+is part of the rapidly exchanging Ca2+compartment noted in45Ca flux studies.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Positron emission tomography is a unique noninvasive imaging technique that provides cross-sectional images of radiotracer concentrations in myocardium and permits measurement of blood flow as well as metabolism. Ammonia and glutamate have been labeled with the positron-emitter13N (half-life 10 minutes) for use with positron emission tomography as tracers of flow and metabolism, respectively. In order to characterize the fate of these13N-labelled compounds in myocardium, isolated rabbit interventricular septa were used to study the kinetics of [13N] glutamate ([3N]glu) and13NH3under aerobic and anoxic conditions. Tissue analyses 6 minutes after injection of a [13N]glu bolus into myocardium revealed that 70% of the13N-label was present in [13N]glu with 12% 11%, and 4% in [13N]alanine ([13N]ala), [13N]aspartate ([13N]asp), and [13N]glutamine ([13N]gln), respectively. The corresponding relative specific activities were 1.0:0.4:0.5:0.01. Anoxia resulted in a significant increase in [13N]ala with a reduction in [13N]glu. This was consistent with increased pyruvate production due to increased anaerobic glycolysis and transamination of pyruvate with [13N]glu to yield [13N]ala. In support of this, addition of 2 mM pyruvate to the perfusate under control conditions produced a tissue distribution of13N similar to that with anoxia. Six minutes after a bolus of13NH3during both control and anoxic conditions, 60% of the tissue13N-label was in [13N]gln with no detectable amounts in other amino acids. The rest of the13N-label was in13NH3. Time-activity curve analyses demonstrated that anoxia significantly reduced the tissue retention of13N-label from13NH3but not from [13N]glu. Thus,13N from13NH3and [13N]glu was retained in tissue by different mechanisms involving glutamate, which were affected differentially by anoxia. These results suggest that positron emission tomography imaging with13NH3and [13N]glu in combination may be useful in identifying ischemic myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The ability of human umbilical endothelial cells to release relaxing substance(s) in response to different agonists was investigated. Endothelium-denuded aortic rings of rats were used for the bioassay and tension recording. After precontraction, this preparation showed no response to histamine, acetylcholine, A 23187, or adenosine triphosphate while serotonin elicited further contraction. Super-fusion of the precontracted preparations with the perfusate from umbilical veins and arteries stimulated with histamine (10−7-10−5M), A23187 (10−7-10−6M), or adenosine triphosphate (10−5-10−4M) elicited a relaxation. No relaxation was obtained with acetylcholine (10−8-10−6M) or serotonin (10−8-10−6M). The relaxation of bioassay aortic rings under the influence of the perfusate from histamine-stimulated umbilical vessels was inhibited by mepyramine (10−5M) but not by cimetidine (10−4M) suggesting the involvement of H1-receptors. The relaxation was also inhibited by increasing the transit time between the donor and the detector preparation, by methylene blue (5 ± 10−5M), and by nordihydroguaiaretic acid (5 ± 10−5M) but not by indomethacin (5 ± 10−5M), characteristics which have been reported for endothelium-derived relaxing factor. The involvement of umbilical endothelial cells in the relaxation response was further confirmed by studying precontracted, rubbed rat aortic rings seeded with cultured endothelial cells from human umbilical veins. Such preparations relaxed in response to histamine (10−7-10−4M) in contrast with the control preparations. No relaxations of these preparations were observed in response to acetylcholine (10−9-10−6M). We conclude that the endothelial cells of the human umbilical blood vessels release an endothelium-derived relaxing factor in response to histamine, acting via H1-receptors, but not in response to acetylcholine.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Whole-cell and single-channel calcium currents in enzymatically isolated dog saphenous vein cells were recorded by the patch-clamp method. Test pulses to negative potentials from holding potentials of −90 to −40 mV elicited currents that inactivated quickly and in a voltage-dependent manner (called Ilowfor low threshold). A second calcium current persisted even at relatively positive holding potentials of − 30 to −10 mV, required stronger depolarizations for maximum current, and inactivated slowly (Ihighfor high threshold). Ihightransported barium more than calcium, whereas Ilowtransported the two ions equally. Single-channel current records (90 mM barium) showed a larger conductance that activated at relatively positive potentials and a smaller (about one-third) conductance that activated at weak depolarizations. Nitrendipine suppressed Ihigh, and the effect was voltage dependent as observed in cardiac cells, although block of resting channels was much greater in vein cells (KR±10−8M). Exposure to the stereoisomer (−)Bay K 8644 increased Ihighbut not Ilow. The (−)Bay K 8644 also increased the channel activity and prolonged the open time of the larger conductance current. Thus, two types of calcium channels, differing in potential-dependence of activation and inactivation, calcium/barium selectivity, single-channel conductance, and sensitivities to dihydropyridines were identified in smooth muscle cells isolated from a large cutaneous vein.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Rat kidneys were isolated and perfused with a modified Krebs-Henseleit buffer containing 4% albumin. Perfusate recirculated except during L-platelet activating factor (L-PAF), angiotensin II (ang II), and norepinephrine (NE) infusions. L-PAF caused a dose-dependent decrease in renovascular resistance (RVR): −6 ± 3% at 10−9M, −12 ± 6% at 10−8M, −18 ± 3% at 10−7M and −20 ± 7% at 10−6M. L-PAF increased immunoreactive PGE (iPGE) and thromboxane (iTXB) release into the venous effluent from 2.4 ± 0.2 to 3.9 ± 0.4 ng/min (p<0.05) and from 2.1 ± 0.4 to 3.5 ± 0.5 ng/min (p<0.05), respectively. Vasodilation by L-PAF (10−7M) in the presence of indomethacin (INDO) (5 μM) was enhanced compared to the non-INDO response (RVR change: L-PAF = −18 ± 3% vs. L-PAF + INDO = −26 ± 3%;p<0.05). As a control for specificity, the structural isomer D-PAF was infused at 10−9M, 10−8M, and 10−7M. None of these concentrations changed renal vascular resistance. To study the vascular receptor responsible for L-PAF-induced vasodilation, dose-response curves to NE and ang II were established with and without L-PAF (10−7M). The NE dose-response curve was unchanged by L-PAF, whereas the ang II dose-response curve was shifted to the right by one order of magnitude. In kidneys pretreated with INDO (5 μM), the L-PAF-induced shift of the ang II dose-response relation was increased to 2–3 orders of magnitude. Renin release was unchanged at 10−9M, 10−8M, and 10−7M L-PAF, but rose threefold at 10−6M concomitant with maximal vasodilation. We conclude that L-PAF is a potent vasodilator of the rat renal vasculature, specifically antagonizing ang-II-induced vasoconstriction. L-PAF also releases prostaglandins, which antagonize the vasodilation. Renin release is increased at a high dose of L-PAF and may be an indirect effect secondary to decreased perfusion pressure.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The myocardial potassium uptake during intracoronary isoproterenol stimulation was characterized in 12 anesthetized pigs. The β-receptor subtype specificity and the effect of adenylate cyclase activation were determined. Potassium concentrations were continuously recorded by PVC-valinomycin minielectrodes in the left atrial cavity and in coronary sinus blood diverted through a shunt to the right atrium. The difference in potassium concentration between the left atrial cavity and coronary sinus, and the accumulated myocardial potassium uptake were calculated after computerized data sampling. By intracoronary drug infusion, changes in heart rate and systemic effects were minimized. Isoproterenol (0.6-0.8 μg/min), a nonspecific β-agonist, reduced coronary sinus potassium concentration transiently to a nadir of 0.28 (0.15-0.43) mM (median and 95% confidence interval) below control values (n = 12). The potassium uptake, which amounted to 140 (79-202) μmol/100 g tissue, corresponding to an intracellular potassium increase of about 3 mM, was abolished after selective β1-blockade by pafenolol. The specific β1-agonist dobutamine (40 μg/min) caused a similar potassium uptake before and after selective β2-blockade by ICI 118, 551. Salbutamol (2 μg/min), a specific β2-agonist, induced a minor potassium uptake of 4 (1-20) μmol/100 g, blocked by pafenolol. After nonselective β-blockade by propranolol the adenylate cyclase stimulator forskolin caused a myocardial potassium uptake of similar magnitude to that of isoproterenol before β-blockade. We conclude that a myocardial potassium uptake ensues during β1-adrenoceptor stimulation and adenylate cyclase activation.

ISSN:0009-7330    

出版商:OVID    

年代:1987

数据来源: OVID