Restoration of myocardial contractile function during gradual reperfusion after total ischemia

Isolated guinea pig hearts subjected to 25-min total normothermic ischemia and 30-min reperfusion with the initial rate exhibited a great rise in isovolumic diastolic pressure while the contractile function recovered to 34 +/- 4% of initial value. Reperfusion with gradually increased rate from 13% of initial rate to 100% resulted in better recovery of the contractile function--to 54 +/- 3% and markedly less rise in the diastolic pressure. This coincided with 28% less inosine loss. More better recovery of the myocardial contractile function (to 80 +/- 5%) was observed in experiments in which gradual reperfusion was combined with recirculation. In both gradual reperfusion series, the recovery of the heart rate and the contractile function were much delayed during first 5 min reperfusion and were associated with a rise in coronary resistance.     

Disorders of cardiac contractile function in ischemic shock; the protective effect of antioxidants and liposomes made from egg phospholipids

Experiments were made on Wistar rats with 6h tourniqueting of the hind limbs to study animal survival rate, myocardial contractile function and protective action of antioxidants and egg phospholipid liposomes during ischemic shock. It has been shown that reperfusion of the limbs leads to a high animal lethality, make lower myocardial contractile function and coronary flow of the hearts isolated from rats following a 6h reperfusion of the limbs. Well-known antioxidant butylated hydroxytoluene and a new antioxidant tetramethylpiperidine derivative bring animal lethality down and improve coronary flow and contractile function of the isolated heart. Phospholipid liposomes increase survival rate moderately but have no any effect on the heart contractile function. It has been deduced that lipid peroxidation takes part in the disturbance of heart contractile function and genesis of the death within ischemic shock.     

Molecular organization of cytokinesis node predicts the constriction rate of the contractile ring

The molecular organization of cytokinesis proteins governs contractile ring function. We used single molecule localization microscopy in live cells to elucidate the molecular organization of cytokinesis proteins and relate it to the constriction rate of the contractile ring. Wild-type fission yeast cells assemble contractile rings by the coalescence of cortical proteins complexes called nodes whereas cells without Anillin/Mid1p (Δmid1) lack visible nodes yet assemble contractile rings competent for constriction from the looping of strands. We leveraged the Δmid1 contractile ring assembly mechanism to determine how two distinct molecular organizations, nodes versus strands, can yield functional contractile rings. Contrary to previous interpretations, nodes assemble in Δmid1 cells. Our results suggest that Myo2p heads condense upon interaction with actin filaments and an excess number of Myo2p heads bound to actin filaments hinders constriction thus reducing the constriction rate. Our work establishes a predictive correlation between the molecular organization of nodes and the behavior of the contractile ring.     

The ionic composition of the contractile vacuole fluid of Paramecium mirrors ion transport across the plasma membrane

In vivo K+, Na+, Ca2+, Cl- and H+ activities in the cytosol and the contractile vacuole fluid, the overall cytosolic osmolarity, the fluid segregation rate per contractile vacuole and the membrane potential of the contractile vacuole complex of Paramecium multimicronucleatum were determined in cells adapted to 24 or 124 mosm l(-1) solutions containing as the monovalent cation(s): 1) 2 mmol l(-1) K+; 2) 2 mmol l(-1) Na+; 3) 1 mmol l(-1) K+ plus 1 mmol l(-1) Na+; or 4) 2 mmol l(-1) choline. In cells adapted to a given external osmolarity i) the fluid segregation rate was the same if adapted to either K+ or Na+, twice as high when adapted to solutions containing both K+ and Na+, and reduced by 50% or more in solutions containing only choline, ii) the fluid of the contractile vacuole was always hypertonic to the cytosol while the sum of the ionic activities measured in the fluid of the contractile vacuole was the same in cells adapted to either K+ or Na+, at least 25% higher in cells adapted to solutions containing both K+ and Na+, and was reduced by 55% or more in solutions containing only choline, iii) the cytosolic osmolarity was the same in cells adapted to K+ alone, to Na+ alone or to both K+ and Na+, whereas it was significantly lower in cells adapted to choline. At a given external osmolarity, a positive relationship between the osmotic gradient across the membrane of the contractile vacuole complex and the fluid segregation rate was observed. We conclude that both the plasma membrane and the membrane of the contractile vacuole complex play roles in fluid segregation. The presence of external Na+ moderated K+ uptake and caused the Ca2+ activity in the contractile vacuole fluid to rise dramatically. Thus, Ca2+ can be eliminated through the contractile vacuole complex when Na+ is present externally. The membrane potential of the contractile vacuole complex remained essentially the same regardless of the external ionic conditions and the ionic composition of the fluid of the contractile vacuole. Notwithstanding the large number of V-ATPases in the membrane of the decorated spongiome, the fluid of the contractile vacuole was found to be only mildly acidic, pH 6.4.     

Role of alpha-adrenergic receptors in the intrinsic inotropic selectivity of dobutamine in anesthetized dogs

The inotropic selectivity of dobutamine was examined in pentobarbital-anesthetized, vagotomized dogs pretreated with a ganglion blocker. The purpose was to determine if, in the presence of hexamethonium and vagotomy, the inotropic selectivity of dobutamine could be attributed to an action of dobutamine on alpha-adrenoreceptors. Dose-response curves were determined for either isoproterenol or dobutamine 30 min after treatment with hexamethonium (20mg/kg). Analysis of heart rate versus right ventricular contractile force showed that dobutamine produced less tachycardia for a given increase in contractile force than isoproterenol; this was statistically significant when contractile force was increased by either 50 or 100%. In a separate series of experiments, dobutamine (8 micrograms . kg(1-) . min(-1)) was administered 20 min after propranolol (3 mg/kg). Under these conditions there was a slight increase in contractile force which represented 12% of the dobutamine response prior to propranolol administration. This increase in contractile force in the presence of propranolol was completely prevented by the addition of phentolamine (1 mg/kg). Consequently, in another series of experiments, dose-response curves for dobutamine were performed in the presence of hexamethonium before and 30 min after phentolamine alone (1 mg/kg) or vehicle. Phentolamine did not influence the effect of dobutamine on heart rate or contractile force, but prevented the increase in diastolic blood pressure caused by dobutamine. In addition, analysis of heart rate versus contractile force indicated that there were no statistically significant effects of phentolamine on the inotropic selectivity of dobutamine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of contraction by gelation/solation in a reconstituted motile model

The actin-based cytoskeleton is a dynamic component of living cells with major structural and contractile properties involved in fundamental cellular processes. The action of actin-binding proteins can decrease or increase the gel structure. Changes in the actin-based cytoskeleton have long been thought to modulate the myosin II-based contractions involved in these cellular processes, but there has been some debate concerning whether maximal gelation increases or decreases contractile activity. To address this question, we have examined how contractile activity is modulated by the extent of actin gelation. The model system consists of physiologically relevant concentrations and molar ratios of actin filaments (whose lengths are controlled by gelsolin), the actin-cross-linking protein filamin, and smooth muscle myosin II. This system has been studied at the macroscopic and light microscopic levels to relate the gel structure to the rate of contraction. We present results which show that while a minimal amount of structure is necessary to transmit the contractile force, increasing the gel structure inhibits the rate of contraction, despite an increase in the actin-activated Mg(2+)-ATPase activity of myosin. Decreasing the total myosin concentration also inhibits the rate of contraction. Application of cytochalasin D to one side of the contractile network increases the rate of contraction and also induces movement comparable to flare streaming observed in isolated amoeba cytoplasm. These results are interpreted relative to current models of the relationship between the state of gelation and contraction and to the potential effects of such a relationship in the living cell.     

The effect of adrenomedullin,amylin fragment 8-37 and calcitonin gene-related peptide on contractile force,heart rate and coronary perfusion pressure in isolated rat hearts

The effect of human adrenomedullin, human amylin fragment 8-37 (amylin 8-37) and rat calcitonin gene-related peptide (CGRP) on contractile force, heart rate and coronary perfusion pressure has been investigated in the isolated perfused rat hearts. Adrenomedullin (2x10(-10), 2x10(-9) and 2x10(-8) M) produced a significant decrease in contractile force and perfusion pressure, but only the peptide caused a decline in heart rate at the highest dose. Amylin (10(-9), 10(-8) and 10(-7) M) significantly increased and then decreased contractile force. Two doses of amylin (10(-8) and 10(-7) M) induced a significant increase in heart rate, however amylin did not change perfusion pressure in all the doses used. Rat alpha CGRP (10(-8), 10(-7) and 10(-6) M) evoked a slight decline in contractile force following a significant increase in contractile force induced by the peptide. CGRP in all the doses raised heart rate and lowered perfusion pressure. Our results suggest that adrenomedullin has negative inotropic, negative chronotropic and coronary vasodilator actions. Amylin produces a biphasic inotropic effect and evokes a positive chronotropy. CGRP causes positive inotropic, positive chronotropic and vasodilatory effects in isolated rat hearts.     

萎缩比目鱼肌间断强直收缩疲劳后恢复速率的影响因素

为研究模拟失重大鼠萎缩比目鱼肌强直收缩疲劳后恢复速率的影响因素,采用尾部悬吊模拟失重大鼠模型及离体骨骼肌条灌流技术,观测其在不同收缩模式下疲劳后的恢复过程。正常大鼠离体比目鱼肌条实验显示,10s短时程（S10P）与300s长时程（L10P）强直收缩轻度疲劳[强直收缩最大张力（P0）下降10％]后,在20min恢复期末,均可恢复至疲劳前P0,且恢复程度不受疲劳持续时间的影响;轻度疲劳后,在灌流液中加入10μmol／L钌红抑制肌浆网Ca^2＋释放功能,恢复速率减慢,恢复程度最大仅至94％P0,然后呈下降趋势,提示轻度疲劳可能仅抑制肌原纤维功能。60s短时程（S50P）与300s长时程（L50P）强直收缩中度疲劳（P0下降50％）后,在20min恢复期末,收缩张力分别恢复至95％P0和90％P0,表明中度疲劳持续时间影响恢复的速率;相同条件中度疲劳后,在灌流液中加入5mmol／L咖啡因促进肌浆网Ca62＋释放功能,恢复速率明显加快,无论疲劳持续时间长短,5min便可完全恢复,提示中度疲劳不仅抑制肌原纤维功能,还抑制肌浆网Ca^2＋释放功能。尾部悬吊1周的大鼠比目鱼肌明显萎缩,其重量／体重之比仅为对照大鼠的60％。采用短与长持续时间的轻与中度疲劳作用后,在20min恢复期末,收缩张力分别恢复至94％P0（S10P）、95％P0（L10P）、92％P0（S50P）、84％P0（L50P）,均与同步对照组有显著差异。以上结果提示：模拟失重1周大鼠萎缩的比目鱼肌,轻度与中度疲劳均可抑制肌原纤维功能与肌浆网Ca^2＋释放功能,使恢复速率减慢。     

Intrinsic factors influencing the maintenance of contractile embryonic heart cells in vitro. 3. The effect of inoculum level

Seven-day embryonic heart cells are tested for their ability to condition their own medium by comparing cell responses at various inoculum levels. The data show that contractile activity, spreading on glass, and survival increase as inoculum level rises. The data also show that the cell death rate is inversely proportional to the rate at which cell spreading and contractile activity increase.     

The response of contractile and non-contractile vacuoles of Paramecium calkinsi to widely varying salinities.

Paramecium calkinsi from tidal marshes survive a wide salinity range. Fluid output of contractile vacuoles of these cells decreased as salinity of the medium to which they were acclimated increased, and both pulse rate and vacuole volume were used to regulate output. When cells were first exposed to more dilute medium, contractile vacuoles greatly increased volume so that fluid output increased even though pulse rate decreased. In cells shifted to a more concentrated medium, contractile vacuole output decreased by decreasing pulse rate. The contractile vacuole is surrounded by a set of collecting structures which change form as the salinity changes. Distensible ampullae are found in media of low salinity and collecting canals are found in media of high salinity. When cells are shifted from high salinity to low, the number of ampullae increases and the number of canals decreases. When cells are shifted from low salinity to high, the number of ampullae decreases and the number of canals decreases. Other non-contracting vacuoles also appear in response to a hypoosmotic shock. These include vacuoles within the cell as well as "blisters" on the surface. The number and frequency of blisters increases with the size of the hypoosmotic shock. They detach from cells without resulting in any visible loss of cytoplasm. Non-contractile vacuoles may play a role in sequestering and removing excess water that the contractile vacuoles cannot handle.     

Intrinsic factors influencing the maintenance of contractile embryonic heart cells in vitro : II. Biochemical analysis of heart muscle conditioned medium

Seven-day embryonic heart cells are tested for their ability to condition their own medium by comparing cell responses at various inoculum levels. The data show that contractile activity, spreading on glass, and survival increase as inoculum level rises. The data also show that the cell death rate is inversely proportional to the rate at which cell spreading and contractile activity increase.     

The Response of Contractile and Non-Contractile Vacuoles of Paramecium calkinsi to Widely Varying Salinities

ABSTRACT. Paramecium calkinsi from tidal marshes survive a wide salinity range. Fluid output of contractile vacuoles of these cells decreased as salinity of the medium to which they were acclimated increased, and both pulse rate and vacuole volume were used to regulate output. When cells were first exposed to more dilute medium, contractile vacuoles greatly increased volume so that fluid output increased even though pulse rate decreased. In cells shifted to a more concentrated medium, contractile vacuole output decreased by decreasing pulse rate. The contractile vacuole is surrounded by a set of collecting structures which change form as the salinity changes. Distensible ampullae are found in media of low salinity and collecting canals are found in media of high salinity. When cells are shifted from high salinity to low, the number of ampullae increases and the number of canals decreases. When cells are shifted from low salinity to high, the number of ampullae decreases and the number of canals decreases. Other non-contracting vacuoles also appear in response to a hypoosmotic shock. These include vacuoles within the cell as well as "blisters" on the surface. The number and frequency of blisters increases with the size of the hypoosmotic shock. They detach from cells without resulting in any visible loss of cytoplasm. Non-contractile vacuoles may play a role in sequestering and removing excess water that the contractile vacuoles cannot handle.     

Engineered early embryonic cardiac tissue retains proliferative and contractile properties of developing embryonic myocardium

Embryonic myocardium has a high rate of cell proliferation and regulates cellular proliferation, contractile function, and myocardial architecture in response to changes in external mechanical loads. However, the small and complex three-dimensional (3D) structure of the embryonic myocardium limits our ability to directly investigate detailed relationships between mechanical load, contractile function, and cardiomyocyte proliferation. We developed a novel 3D engineered early embryonic cardiac tissue (EEECT) from early embryonic ventricular cells to test the hypothesis that EEECT retains the proliferative and contractile properties of embryonic myocardium. We combined freshly isolated White Leghorn chicken embryonic ventricular cells at Hamburger-Hamilton (HH) stage 31 (day 7 of a 46-stage, 21-day incubation period), collagen type I, and matrix factors to construct cylindrical-shaped EEECTs. We studied tissue architecture, cell proliferation patterns, and contractile function. We then generated engineered fetal cardiac tissue (EFCT) from HH stage 40 (day 14) fetal ventricular cells for direct comparison with EEECT. Tissue architecture was similar in EEECT and EFCT. EEECT maintained high cell proliferation patterns by culture day 12, whereas EFCT decreased cell proliferation rate by culture day 9 (P < 0.05). EEECT increased active contractile force from culture day 7 to day 12. The culture day 12 EEECT contractile response to the beta-adrenergic stimulation was less than culture day 9 EFCT (P < 0.05). Cyclic mechanical stretch stimulation induced myocardial hyperplasia in EEECT. Results indicate that EEECT retains the proliferative and contractile properties of developing embryonic myocardium and shows potential as a robust in vitro model of developing embryonic myocardium.     

Counting actin in contractile rings reveals novel contributions of cofilin and type II myosins to fission yeast cytokinesis

Cytokinesis by animals, fungi, and amoebas depends on actomyosin contractile rings, which are stabilized by continuous turnover of actin filaments. Remarkably little is known about the amount of polymerized actin in contractile rings, so we used low concentrations of GFP-Lifeact to count total polymerized actin molecules in the contractile rings of live fission yeast cells. Contractile rings of wild-type cells accumulated polymerized actin molecules at 4900/min to a peak number of ∼198,000 followed by a loss of actin at 5400/min throughout ring constriction. In adf1-M3 mutant cells with cofilin that severs actin filaments poorly, contractile rings accumulated polymerized actin at twice the normal rate and eventually had almost twofold more actin along with a proportional increase in type II myosins Myo2, Myp2, and formin Cdc12. Although 30% of adf1-M3 mutant cells failed to constrict their rings fully, the rest lost actin from the rings at the wild-type rates. Mutations of type II myosins Myo2 and Myp2 reduced contractile ring actin filaments by half and slowed the rate of actin loss from the rings.     

Circulatory responses to selective stimulation of medullated and non-medullated fibers of the aortic nerve

Circulatory responses to selective afferent stimulation of medullated and non-medullated fibers in the left aortic nerve were followed in terms of changes in arterial pressure, heart rate, contractile force of the left ventricular fragment and vascular resistance of the hind limb of cats with an opened thorax. Stimulation of the medullated afferents induced a reflex fall of blood pressure mainly by means of decrease in the peripheral vascular resistance, while activation of non-medullated fibers influenced the heart work, i. e. decreased heart rate and myocardial contractile force.     

Load dependence of ventricular performance explained by model of calcium-myofilament interactions

Although a simple concept of load-independent behavior of the intact heart evolved from early studies of isolated, intact blood-perfused hearts, more recent studies showed that, as in isolated muscle, the mode of contraction (isovolumic vs. ejection) impacts on end-systolic elastance. The purpose of the present study was to test whether a four-state model of myofilament interactions with length-dependent rate constants could explain the complex contractile behavior of the intact, ejecting heart. Studies were performed in isolated, blood-perfused canine hearts with intracellular calcium transients measured by macroinjected aequorin. Measured calcium transients were used as the driving function for the model, and length-dependent rate constants yielding the highest concordance between measured and model-predicted midwall stress at different isovolumic volumes were determined. These length-dependent rate constants successfully predicted contractile behavior on ejecting contractions. This, along with additional model analysis, suggests that length-dependent changes in calcium binding affinity may not be an important factor contributing to load-dependent contractile performance in the intact heart under physiological conditions.     

Study of cardio- and hemodynamic reactions to administration of GABA into the neuronal structures of the ventrolateral area of the medulla oblongata of cats

The data obtained in acute experiments on cats have indicated that the most GABA-sensitive injected neuronal structures in the ventrolateral medulla appear to be located in the vicinity to the roots of the XII cranial nerves. GABA injected into these structures just rostrally to the roots induced hypotensive reactions due to heart rate and myocardial contractile activity decrease, besides inhibition of sympathetic vasoconstrictor influences. GABA injected into the neuronal structures in the caudal ventrolateral medulla induced hypertensive reactions, to a large extent due to increase in heart rate and contractile activity of myocardium.     

The Role of the Contractile Vacuole in the Osmoregulation of Tetrahymena pyriformis*

The relationship of cell size and contractile vacuole efflux to osmotic stress was studied in Tetrahymena pyriformis strain W, after transfer into fresh solutions iso- or hypoosmotic to the growth medium. Microscopic measurements of the cell and contractile vacuole dimensions, made with an image-sharing ocular at 27 C, allowed the calculation of the cell size and shape and the vacuolar efflux rate which provide a measure of osmoregulation. The contractile vacuole cycles have no homeostatic oscillations. In 0.03–0.10 osmolar solutions, the cell size and shape are constant while the vacuolar efflux rate has an inverse linear dependence upon extracellular osmolarity. Regression analyses indicate that for cells with systole faster than 0.1 sec (the major part of the population), it is only the final diastolic volume of the contractile vacuole that is related to osmotic stress while the frequency of systole is independent of osmotic stress and has a constant period of 7.7 ± 0.2 sec. Therefore, osmotic stress upon Tetrahymena is regulated by a corresponding change in the filling rate of its contractile vacuole to allow an unaltered cell size and shape. Kinetic measurements of vacuoles during diastole fit the model (dV/dt = K_1-K₂A), where (dV/dt) is the vacuolar filling rate and (A) is the vacuolar surface area. This dependence of vacuolar volume upon its surface area may be ascribed either to elastic components of the vacuolar membrane or to an increasing leakiness of this membrane during diastole. Mitochondrial inhibitors were used to observe the energy requirements of vacuolar operation and of intracellular secretion of water.     

Stress-induced inhibition of the ileal, caecal, and colonic contractile activity in rabbits]

In alert rabbits, immobilisation stress decreased the spike burst rate and amplitude in ileum, caecum, and colon for 20 min. Following beta-adrenoceptor blockade, the contractile activity suppression was aggravated. The stress seems to lead to suppression of the ileal, caecal, and colonic contractile activity for up to 40 min which is unrelated to adrenergic inhibition of the smooth muscle activity mediated by beta-adrenoceptors.     

Structure of the cardiac systole in mammals and birds

The comparative analysis of the contractile function of the heart left ventricle in four species of homoeothermic tetrapods (chicken, quail, rat, sheep) who differ in their spatio-temporal pattern of ventricular excitation, heart rate, and heart weight was performed. The analysis of cardiac cycle structure was performed on the basis of synchronous recording of ECG, phonocardiogram, and apex cardiogram. Indices of myocardial contractility of the left ventricle calculated on the basis of the analysis of the cardiac dynamics indicate disadvantageous contractile function of the left ventricle in rodents and non-flying birds in comparison with sheep. The functioning of the left ventricle in male rats is more strained than in female rats. One fundamental factor determining a more strained functioning of the left ventricle in birds in comparison with mammals is the heart rate. The relative weight and activation pattern of the left ventricular myocardium govern the contractile function of the left ventricle to a lesser extent.