摘要:

Ventricular arrhythmias that accompany myocardial infarction in dogs may be secondary to the altered electrophysiological properties of the subendocardial Purkinje fibers that survive 24 hours after the coronary occlusion. To better understand the ionic mechanisms that underlie the altered electrical activity of these fibers, we have dispersed, using an enzymatic technique, Purkinje cells from the subendocardium of the infarcted ventricle (IZPCs) and compared their electrical and structural properties to Purkinje cells dispersed from fiber strands (SPCs) and from the subendocardium of the noninfarcted ventricle (NZPCs). Ultrastructural analysis of these cells shows that IZPCscontain an increased number of lipid droplets when compared with the SPCs and NZPCs. In addition, transmembrane action potentials of IZPCshave reduced resting potentials, action potential amplitudes, and upstroke velocity and are increased in duration when compared with either SPCs or NZPCs. Input resistance of IZPCs is increased over that measured in control cells (SPCs and NZPCs). Furthermore, the time course of the process of electrical restitution of action potential duration is altered in IZPCs with long action potentials. Finally, using K+M-sensitive microelectrode techniques, we have determined that intracellular free K+activity (aK1) in IZPCs(93.7 ± 15 niM) is not significantly different from control aK1measurements (SPC, 106 ± 13 mM; NZPC, 103 ± 12 mM). Thus a reduction in aK1does not provide a basis for the reduced resting potentials observed in IZPCs. By studying the relation between the resting potential and log [K+]owe determined that in IZPCswith reduced resting potentials, there is a significant increase in the PNa/PKratio when compared with control. In summary, to better understand the cellular basis of ventricular arrhythmias postinfarction, we have developed a single cell model that will allow for more rigorous electrophysiological studies of the specific ionic currents that underlie the abnormal electrophysiology.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The effects of near-maximal coronary vasodilation were examined in conscious dogs with left ventricular (LV) failure after pressure overload hypertrophy induced by either aortic banding alone or aortic banding plus a peripheral arteriovenous shunt. The findings were compared with results in littermates with compensated LV hypertrophy and with a third group of normal dogs. At rest, there was a marked difference in the intramyocardial distribution of coronary flow, measured with radiolabeled microspheres. The endocardial/epicardial (endo/epi) flow ratio in the LV failure dogs was 0.96 ± 0.08 as compared with control dogs (1.28 ± 0.06,p<0.05) or dogs with compensated LV hypertrophy (1.23 ± 0.08,p<0.05). During near-maximal coronary vasodilation with adenosine, all groups showed similar increases in subepimyocardial (epi) flow. While significant increases in subendomyocardial (endo) flow during adenosine infusion were seen in the control group (0.88 ± 0.10 to 3.53 ± 0.24 ml/min/g) and in dogs with compensated LV hypertrophy (1.12 ± 0.14 to 3.60 ± 0.16 ml/min/g), there was no change in endo flow in the LV failure dogs (1.55 ± 0.20 to 1.71 ± 0.47 ml/min/g) and a further significant reduction in the endo/epi flow ratio was observed (030 ± 0.06,p<0.01). These hemodynamic changes were associated with chronic multifocal interstitial or discrete areas of fibrosis observed preferentially in endo layers. Thus, endo flow reserve is nearly exhausted in dogs with decompensated pressure overload LV hypertrophy, which may induce periodic episodes of endo ischemia resulting in myocyte necrosis and fibrosis, which in turn results in exacerbation of LV failure.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A fatty acid-binding protein (FABP) was purified from rabbit heart and characterized with respect to size, isoelectric point, and tissue distribution. This protein was found in red muscle, diaphragm, and aorta, as well as in the heart. Amino acid composition of rabbit heart FABP differed only slightly from the human and rat proteins. Rabbit heart FABP was shown to bind two molecules of fatty acid. A monoclonal antibody was developed and used to demonstrate the feasibility of a one-step purification with affinity chromatography. Cross-reactivity was found between the human protein and the rabbit antibody, and an immunoassay was developed to human heart FABP. Levels of human heart FABP in the plasma of patients with acute myocardial infarction were significantly elevated (83 ± 9 μg/ml) compared with patients with pulmonary edema (52 ± 7 μg/ml) and normal volunteers (28 ± 5 μg/ml;p< O.OS, mean ± SEM).

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The incorporation of32P1into phospholamban, troponin I, phosphatidylinositols, and inositol trisphosphates was studied in Langendorff-perfused guinea pig hearts stimulated with isoproterenol. Hearts were perfused with Krebs-Henseleit buffer containing [32P]P|and freezeclamped at different times during the positive inotropic response. Exposure of the hearts to 0.1 μM isoproterenol for up to 1 minute was associated with significant (up to threefold) increases in phospholamban and troponin I phosphorylation, but there was no significant increase in32P incorporation into phospholipids. However, longer exposure (2 minutes or more) to isoproterenol was associated with increases in the degree of P labeling of phosphatidylinositols and phosphatidic acid. Examination of32P labeling of Inositol trisphosphates in the same hearts revealed that the radioactivity associated with these compounds decreased with time. The decreases were significant at times of exposure of 2 minutes or longer to β-adrenergic stimulation. The tissue levels of the inositol 1,4,5-trisphosphate isoform were also measured in hearts perfused with isoproterenol for 3 minutes, and they were found to be significantly lower compared with values obtained in control hearts. The effects of isoproterenol on32P incorporation into phospholipids and proteins were observed in the presence of prazosin, and they were completely abolished by the β-receptor blocker propranolol. Examination of the phosphoinositldespecific phosphoUpase C activity in the perfused hearts revealed that isoproterenol stimulation was associated with a decrease in the membrane-associated enzymatic activity at physiological calcium concentrations. These findings indicate that β-adrenergic stimulation of isolated hearts is associated with changes in basal phosphatidylinositol turnover that may be mediated, at least in part, by inhibition of the phosphoUpase C enzymatic activity specific for phosphatidylinositols.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The escape of solutes from the blood during passage along capillaries hi heart and skeletal muscle occurs via diffusion through clefts between endothelial cells and, for some solutes, via adsorption to or transport across the luminal plasmalemma of the endothelial cell. To quantitate the rates of permeation via these two routes of transport across capillary wall, we have developed a linear model for transendothelial transport and Illustrated its suitability for the design and analysis of multiple simultaneous indicator dilution curves from an organ. Data should be obtained for at least three solutes: 1) an intravascular reference, albumin; 2) a solute transported by endothelial cells; and 3) another reference solute, of the same molecular size as solute 2, which neither binds nor traverses cell membranes. The capillary-tissue convectionpermeation model is spatially distributed and accounts for axial variation in concentrations, transport through and around endothelial cells, accumulation and consumption within them, exchange with the interstitium and parenchyma! cells, and heterogeneity of regional flows. The upslope of the dilution curves is highly sensitive to unidirectional rate of loss at the luminal endothelial surface. There is less sensitivity to transport across the antiluminal surface, except when endothelial retention is low. The model is useful for receptor kinetics using tracers during steady-state conditions and allows distinction between equilibrium binding and reaction rate limitations. Uptake rates at the luminal surface are readily estimated by fitting the model to the experimental dilution curves. For adenosine and fatty acids, endothelial transport accounts for 30-99% of the transcapillary extraction.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

General anesthetics, typically octanol, were found to inhibit the influx of calcium in isolated sodium-loaded adult rat heart cells, using45Ca, quin 2, or indo 1. Inhibition by octanol, like inhibition by sodium, was competitive with calcium. Octanol and sodium together inhibited calcium influx synergistically. At physiological levels of extracellular calcium and sodium, the EC50was 177 ± 37 μM for octanol and 48 ± 5 μM for decanol. These values are threefold to fourfold larger than those reported to cause 50% loss of righting reflex in tadpoles, a measure of their anesthetic effectiveness. We conclude that general anesthetics inhibit Na-Ca exchange at the sarcokmma. We suggest that octanol inhibits like sodium, and the synergism stems from the cooperativity of sodium inhibition at the binding and regulatory sites of the exchanger. Insofar as Na-Ca exchange may regulate inotropy, the inhibition of Na-Ca exchange by general anesthetics could contribute to their negative inotropic effect.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

In studies of ischemia and reperfusion, a major experimental problem has been the inability to measure intracellular ionized calcium ([Ca2+])) in the intact heart. We have developed a new approach in which the bioluminescent calcium indicator aequorin is used to measure [Ca2+]i, in the isolated, coronary-perfused ferret heart. Aequorin is loaded into subepicardial myocytes of the left ventricle, and the signals are recorded simultaneously along with isovolumic left ventricular (LV) pressure at a constant pacing rate. This system shows 1) no attenuation or change of time course of LV pressure development or coronary perfusion pressure after aequorin loading; 2) consistent responses to physiological interventions and drugs; 3) individual aequorin and pressure signals that do not require signal averaging for analysis; and 4) [Ca2+]i, levels comparable with those reported in tissue or isolated myocyte cell preparations. During 5 minutes of hypoxia, diastolic [Ca2+)iand LV diastolic pressure increased while the systolic values of both [Ca2+]iand pressure decreased. The peak-to-peak systolic [Ca2+]iversus LV isovolumic pressure relation remained close to the control curve. In contrast, during 3 minutes of global ischemia, LV systolic and diastolic pressures fell rapidly, while [Ca2+]iincreased substantially. The [Ca2+]iversus pressure relations for both systole and diastole shifted to the right, indicating desensitization of the contractile apparatus to [Ca2+]i. These results provide evidence that different primary mechanisms determine the systolic and diastolic responses to acute hypoxia versus ischemia. During hypoxia, changes in [Ca2+]ihandling probably play a major role, while during ischemia, changes in the Ca2+sensitivity of the myofilaments appear to be of primary importance in the modulation of contractile dysfunction.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The roles of H+-Na+and Na+-Ca2+exchange in the depression of ventricular function were studied in the reperfused isolated ischemic rat heart. Zero-flow global ischemia was induced for either IS or 30 minutes and was followed by 30 minutes of aerobic reperfusion. Intracellular Na+(Na+i) and45Ca2+uptake were measured during ischemia and reperfusion. Accumulation of Na+, was modified by prior grycogen depletion and by treatment with amiloride, a H+-Na+exchange inhibitor, or monensin, a Na+ionophore. Na+irose continuously during ischemia and rapidly during the first two minutes of reperfusion. The larger inhibitory effect of amiloride and preischemic glycogen depletion was on Na+iaccumulation during reperfusion; this finding suggests that the uptake occurs by H+-Na+exchange. Reduction of Na+iaccumulation by glycogen depletion was associated with less lactate and, presumably, H+production and accumulation during ischemia. The rapid increase in Na+iduring early reperfusion may reflect the readjustment of the low intracellular pH resulting from ischemia. The level of Na+iat the end of ischemia and especially after two minutes of reperfusion were linearly correlated with45Ca2+uptake and depression of ventricular function during subsequent reperfusion. This highly significant correlation between Na+iand45Ca2+uptake when Na+iwas varied by several independent procedures, including monensin, strongly suggests that reperfiision45Ca2+uptake occurs at least in part by Na+-Ca2+exchange. The rate of45Ca2+uptake during reperfusion was linearly and highly significantly correlated with elevation of diastolic pressure, reduced developed pressure, and decreased recovery of ventricular function. The data strongly support a mechanism of ischemic cell damage that involves excessive production and accumulation of H+during Ischemia that exchanges for extracellular Na+during ischemia and rapidly during the first few minutes of reperfusion. Increased Na+ithen causes excessive45Ca2+uptake and depressed recovery of cellular functions with continued reperfusion. Increased levels of Na+imay be a major event that couples a decreased intracellular pH during ischemia to excessive45Ca2+uptake and depressed recovery of cellular function with reperfusion.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Endothelial cell (EC) injury and the response of EC and smooth muscle cells (SMCs) to injury contribute to the pathophysiology in patients with vascular disease and atherosclerosis. Since platelets have been suggested to play an important role in modulating vascular injury, the present study was undertaken to examine the influence and mechanism of action of individual platelet factors on bovine aortic EC and SMC migration using an in vitro wound assay system. Serotonin decreased EC proliferation and reduced EC migration 21 ± 1% (p<0.005), which was attenuated by imipramine. Transforming growth factor-β reduced EC proliferation and decreased EC migration 52 ± 3% (p<0.005). Norepinephrine increased EC proliferation but decreased EC migration 26 ± 2% (p< 0.005), which was abolished by phenoxybenzamine. Histamine increased EC proliferation but reduced EC migration 29 ± 2% (p< .005), which was attenuated by diphenhydramine. Platelet-derived growth factor decreased EC proliferation and decreased EC migration 40 ± 2% (p<0.005). In contrast, serotonin increased SMC proliferation and increased SMC migration 31 ± 2% (p<0.005), which was abolished by ketanserin. Transforming growth factor-β increased SMC migration 35 ± 5% (p<0.005). Norepinephrine increased SMC proliferation and increased SMC migration 43 ± 4% (p<0.005), which was abolished by propranolol. Histamine increased SMC proliferation and increased SMC migration 38 ± 3% (p<0.005), which was abolished by cimetidine. Platelet-derived growth factor increased SMC proliferation and increased SMC migration 40 ± 3% (p<0.005). Changes in migration were unaffected by growth-arresting treatment. Hence, these individual platelet factors inhibit EC migration and augment SMC migration via specific receptors and independent of proliferation changes. These results suggest mechanisms in which platelet factors may contribute to blood vessel injury in vivo.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Experiments were carried out in hearts from guinea pigs that were fed either the adenosine receptor antagonist theophylline (0.6 mg/ml) or no drug. The Aiadenosine receptor radioligand [125l]aminobenzyladenosine bound to a single affinity class of receptors in heart cell membranes from control animals with Bmaxand KDof 183 ± 1.0 fmol/mg protein and 3.7 ± 0.6 nM, respectively (n=8). Heart cell membranes from animals fed theophylline for 2, 7, and 14 days bound the radioligand with about the same affinity, but the number of binding sites was significantly increased (p<0.01) to 30.6 ± 1.7 (n=3), 30.0 ± 0.8 (n=3), and 27.3 ± 2.9 (n=4), respectively. Nearly identical results were obtained with membranes prepared from enzymatically dispersed ventricular myocytes. Fourteen days of theophylline treatment also produced a small increase (12%,p< 0.01) in the number of binding sites in membranes derived from cerebral cortexes. Isolated ventricular myocytes prepared from animals fed no drug or theophylline for 7 days were used to determine the effect of adenosine on 20 nM isoproterenolstimulated calcium current (Icameasured by the whole-cell patch-clamp technique. Adenosine reduced isoproterenol-stimulated Icawithout affecting the activation or inactivation kinetics of the current; Icadensity was reduced less by 5 μM adenosine in cells from control (25 ± 3 to 21 ± 3 μA/μF) than in cells from theophylline-fed animals (26 ± 5 to 17 ± 2 μA/μF). Although a high concentration (0.5 mM) of adenosine abolished isoproterenol-stimulated Icain cells from control or theophylline-fed animals, the IC50for adenosine was sixfold less in cells derived from theophylline-fed animals than in cells from control animals (4.6 ± 0.6 μM and 283 ± 1.4 μM, respectively,p< 0.01). In contrast, the increase in Icain response to isoproterenol alone and the potency of acetylcholine to antagonize this effect of isoproterenol were the same in both groups of cells. A maximally effective concentration ofR-phenylisopropyladenosine (0.1 mM) inhibited isoproterenol-stimulated cyclic AMP accumulation less in cardiomyocytes from control than from theophylline-fed animals (28.7 ± 1.8% vs. 42.0 ± 4.2%,p< 0.05). In summary, exposure of the myocardium to theophylline increases the number of adenosine receptors and the effects of receptor occupancy by agonists. These findings imply that the endogenous concentration of adenosine is high enough in the normoxic guinea pig heart to chronically maintain adenosine receptors in a partially down-regulated state.

ISSN:0009-7330    

出版商:OVID    

年代:1989

数据来源: OVID