bluuebunny/crossref_metadata_2025 huggingface dataset:
Decreased endothelium-dependent hyperpolarization to acetylcholine in smooth muscle of the mesenteric artery of spontaneously hypertensive rats.
Authors: Fujii K , Tominaga M , Ohmori S , Kobayashi K , Koga T , Takata Y , Fujishima M
Published: June 2012

The endothelium-dependent vascular relaxation to acetylcholine (ACh) in spontaneously hypertensive rats (SHR) may be impaired because of an imbalance of endothelium-derived relaxing factor and contracting factor. However, the role of the endothelium-dependent hyperpolarization remains undetermined. We examined the ACh-induced hyperpolarization and its contribution to relaxation in arteries of SHR. Membrane potentials were recorded from the mesenteric artery trunk of 6-8-month-old male SHR and also Wistar-Kyoto (WKY) rats. Endothelium-dependent hyperpolarization to ACh was unaffected by NG-nitro-L-arginine, indomethacin, or glibenclamide; was reduced by tetraethylammonium or high K+ solution; and was enhanced by low K+ solution or methylene blue, thereby indicating that hyperpolarization is not mediated by nitric oxide (endothelium-derived relaxing factor) but is presumably mediated by a hyperpolarizing factor and is due to an opening of K+ channels that probably differ from the ATP-sensitive ones. Hyperpolarizations to ACh were markedly reduced in SHR compared with findings in WKY rats (maximum, 8 +/- 1 versus 17 +/- 1 mV). In addition, under conditions of depolarization with norepinephrine (10(-5) M), the ACh-induced hyperpolarization was even less and transient in SHR, while it was large and sustained in WKY rats (6 +/- 1 versus 29 +/- 2 mV). Endothelium-dependent relaxations to ACh in arterial rings precontracted with 10(-5) M norepinephrine were far less in SHR than in WKY rats, even in the presence of indomethacin. Furthermore, high K+ solution showed smaller inhibitory effects on the relaxations in SHR than in WKY rats. Endothelium-independent hyperpolarizations and relaxations to cromakalim, a K+ channel opener, were similar between SHR and WKY rats. It would thus appear that the endothelium-dependent hyperpolarization to ACh is reduced in SHR and this would, in part, account for the impaired relaxation to ACh in SHR mesenteric arteries.
Effect of alpha-adrenergic stimulation on activation of protein kinase C and phosphorylation of proteins in intact rabbit hearts.
Authors: Talosi L , Kranias E G
Published: June 2012

The intracellular events and specifically the role of protein kinase C-mediated protein phosphorylation, after alpha-adrenergic receptor stimulation of the heart, are not well understood. We examined the phosphorylation of sarcolemmal, sarcoplasmic reticular, myofibrillar, and cytosolic proteins in perfused beating rabbit hearts on activation of protein kinase C by phenylephrine. Perfusion of rabbit hearts with phenylephrine was associated with a positive inotropic response, which was dose and time dependent. Maximal stimulation (1.54-fold increase in +dP/dt) was obtained with 10 microM phenylephrine at 4 minutes. Examination of the activity levels of protein kinase C in these hearts revealed a redistribution of this activity from the cytosolic to the membranous fraction, suggesting the activation of this enzyme in vivo. Prazosin, an alpha 1-adrenergic antagonist, prevented the increase in the inotropy and the redistribution of protein kinase C activity mediated by phenylephrine. Examination of the degree of phosphorylation of membranous, myofibrillar, and cytosolic proteins revealed that activation of protein kinase C in vivo was associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein. There were no increases in the degree of phosphorylation of phospholamban in the sarcoplasmic reticulum and of troponin I, troponin T, and C protein in the myofibrils, although these proteins were found to be substrates for protein kinase C in vitro. These findings provide evidence that protein kinase C is activated in response to alpha-adrenergic stimulation and that activation is associated with increased phosphorylation of a 15-kd sarcolemmal protein and a 28-kd cytosolic protein in the myocardium.
Effect of field stimulation on cellular repolarization in rabbit myocardium. Implications for reentry induction.
Authors: Knisley S B , Smith W M , Ideker R E
Published: June 2012

We have investigated the effects of electric field stimulation on membrane repolarization in rabbit papillary muscles and assessed the consequences of these effects for the dispersion of intracellular potentials and the production of a propagation wave front or unidirectional block in relatively refractory tissue. The stimuli studied had electric field strength of 0.25-14 V/cm, duration of 2 msec, and field orientation along or across the myocardial fibers. The field strengths to excite the muscles in diastole were 0.68 or 1.23 V/cm for stimuli oriented along or across the fibers, respectively (p less than 0.01, along versus across). A 2.5-V/cm stimulus given near the end of the action potential (AP) produced either no response or, after increasing the stimulus delay only 2-3 msec, a full response with almost no AP durations that were intermediate. For stimulation along and across the fibers, respectively, given at 70% of the AP duration, a 4-V/cm stimulus produced AP prolongation (measured at 90% repolarization) of 20% and 4% (p less than 0.05), an 8-V/cm stimulus produced AP prolongation of 36% and 20% (p less than 0.05), and a 14-V/cm stimulus produced AP prolongation of 36% and 30% (p = NS). For either orientation, AP prolongation by stimuli of 8 V/cm or 14 V/cm increased gradually as the stimulus delay was increased. The different effects in relatively refractory tissue of stimuli of 2.5 V/cm compared with 8 V/cm can explain the propagation wave front and block that occur with electrically induced functional reentry in the heart.(ABSTRACT TRUNCATED AT 250 WORDS)
Existence of both fast and slow channel activity during the early stages of ventricular fibrillation.
Authors: Zhou X , Guse P , Wolf P D , Rollins D L , Smith W M , Ideker R E
Published: June 2012

Although sodium channels have been reported to be inactive after 5-10 minutes of ventricular fibrillation (VF), their state during early VF is unknown. In 12 open-chest dogs, a floating glass microelectrode was used to record intracellular action potentials from the right ventricle during pacing and during electrically induced VF. Before any drug was administered, an initial episode of VF was continuously recorded for at least 20 seconds followed by defibrillation. Recordings were made during VF episodes after superfusion for 15 minutes around the microelectrode site by low (2.8 x 10(-5) M) and high (10(-4) M) concentrations of tetrodotoxin (TTX) in five dogs, or by low (4 microM) and high (100 microM) concentrations of verapamil in another four dogs. In three dogs, VF was induced without drugs three times to determine if the effects observed in the previous dogs were caused by the drugs or by successive episodes of VF. Ten consecutive action potentials were analyzed at the onset and after 5, 10, 15, and 20 seconds of VF. Action potential amplitude and duration during paced rhythm or VF were not changed by the local perfusion of either TTX or verapamil. In the TTX group, the maximum upstroke rate of depolarization of an action potential (Vmax) during paced rhythm was 104 +/- 14 V/sec for control cycles before any drug was given, 86 +/- 15 V/sec for the low TTX concentration, and 55 +/- 14 V/sec for the high TTX concentration (p less than 0.05 versus other two). Vmax decreased from 55 +/- 32 V/sec at the beginning of VF to 37 +/- 27 V/sec after 20 seconds of VF for predrug VF, from 39 +/- 20 V/sec to 18 +/- 11 V/sec for low-dose TTX VF, and from 18 +/- 13 V/sec to 12 +/- 7 V/sec for high-dose TTX VF (p less than 0.05 among the three groups). In the dogs receiving verapamil, VF was still inducible with Vmax not significantly different from predrug VF at the onset and after 5 or 20 seconds of VF but with Vmax smaller (p less than 0.05) for verapamil than for predrug VF after 10 or 15 seconds of VF. In three dogs, Vmax was not significantly different during three successive episodes of VF when no drug was given between the episodes.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of calcium on shortening velocity in frog chemically skinned atrial myocytes and in mechanically disrupted ventricular myocardium from rat.
Authors: Hofmann P A , Moss R L
Published: June 2012

Effects of [Ca2+] on isometric tension and unloaded shortening velocity were characterized in single chemically skinned myocytes from frog atrium and in mechanically disrupted myocardium from rat ventricle. The preparations were attached to a force transducer and piezoelectric translator and were viewed with an inverted microscope to allow continuous monitoring of sarcomere length during mechanical measurements. Unloaded shortening velocity was determined by measuring the time required to take up various amounts of slack imposed at one end of each preparation. Ca2+ sensitivity of isometric tension was assessed as pCa50, i.e., the Ca2+ concentration at which tension was 50% maximal, and was greater for frog atrial myocytes (pCa50 6.17) than for rat ventricular myocytes (pCa50 6.06). This difference in Ca2+ sensitivity may be due to variations in myofibrillar protein isoform composition in the two preparations. Inclusion of caffeine in the activating solutions substantially increased the Ca2+ sensitivity of tension, which may be a manifestation of a direct effect of caffeine on the myofibrillar proteins. Unloaded shortening velocity during maximal activation averaged 4.32 muscle lengths per second in frog atrial myocytes and 4.46 muscle lengths per second in rat ventricular myocytes. When [Ca2+] was reduced, unloaded shortening velocity decreased substantially in both preparations. Possible mechanisms for the effect of Ca2+ on shortening velocity in myocardium include Ca2+ dependence of the rate of ADP dissociation from actomyosin complexes or a shortening-dependent internal load involving structures such as C protein or long-lived myosin cross-bridges.
Effect of cyclooxygenase blockade on blood flow through well-developed coronary collateral vessels.
Authors: Altman J , Dulas D , Bache R J
Published: June 2012

Collateral vessels that develop after coronary artery occlusion demonstrate perivascular inflammation, subintimal hyperplasia, and endothelial proliferation. This study was performed to test the hypothesis that these abnormalities are associated with evidence for increased production of vasodilator prostaglandins. Eight dogs were studied 4-6 months after occlusion of the anterior descending coronary artery had been performed to stimulate collateral vessel growth. At the time of study, the anterior descending coronary artery was cannulated at the site of occlusion to allow measurement of retrograde blood flow as an index of interarterial collateral flow. Injection of radioactive microspheres during the retrograde flow collection allowed determination of continuing tissue flow in the collateral-dependent zone as an index of intramural microvascular collateral flow. Retrograde and tissue flows were measured before and 20 minutes after 5 mg/kg i.v. indomethacin, a dose that caused 95 +/- 3% inhibition of the coronary vasodilation in response to a 500 micrograms intracoronary bolus of arachidonic acid. Heart rate and mean aortic pressure were not significantly altered by indomethacin, and blood flow to the normally perfused myocardial region was not changed by administration of indomethacin. However, indomethacin caused a 40 +/- 7% decrease in retrograde flow (p less than 0.01), and microvascular collateral flow to the dependent myocardium decreased by 20 +/- 10% (p less than 0.05). These data indicate that, unlike the normal coronary circulation, well-developed coronary collateral vessels are under the tonic influence of vasodilator prostaglandins.
Phenotype-related alteration in expression of natriuretic peptide receptors in aortic smooth muscle cells.
Authors: Suga S , Nakao K , Kishimoto I , Hosoda K , Mukoyama M , Arai H , Shirakami G , Ogawa Y , Komatsu Y , Nakagawa O
Published: June 2012

To elucidate the physiological and pathophysiological roles of the natriuretic peptide family in vascular smooth muscle cells, in which the natriuretic peptide family is implicated in growth inhibition as well as vasorelaxation, we have examined the phenotype-related expression of three kinds of natriuretic peptide receptors in rat aortic smooth muscle cells. The expression of natriuretic peptide receptors at the mRNA level was studied by Northern blot hybridization, and the expression at the protein level was determined by the cGMP production method and receptor binding assay. In intact aortic media, atrial natriuretic peptide (ANP)-A receptor mRNA and ANP-B receptor mRNA were detected, and the potency of cGMP production by ANP was at least two orders of magnitude stronger than that by C-type natriuretic peptide. Clearance receptor mRNA was undetectable, and only a small amount of the clearance receptor was detected by the binding assay in intact aortic media. By contrast, in cultured aortic smooth muscle cells at the first, fifth, and 17th passages, the ANP-B receptor mRNA level markedly increased; meanwhile, the expression of the ANP-A receptor mRNA became undetectable. C-type natriuretic peptide was one order of magnitude more potent than ANP in cGMP production in cultured aortic smooth muscle cells. The clearance receptor density and its mRNA level increased tremendously in these cultured cells. These results demonstrate that the marked phenotype-related alteration occurs in the expression of natriuretic peptide receptors in rat aortic smooth muscle cells.
Role of epicardial mesothelial cells in the modification of phenotype and function of adult rat ventricular myocytes in primary coculture.
Authors: Eid H , Larson D M , Springhorn J P , Attawia M A , Nayak R C , Smith T W , Kelly R A
Published: June 2012

Adult rat ventricular myocytes undergo a well-documented sequence of phenotypic changes during adaptation to primary culture. However, we observed that coculture of myocytes with a specific subset of nonmyocyte cardiac cells could slow and even reverse the process of adaptation. These nonmyocyte cells were isolated and identified by immunohistochemical and ultrastructural criteria as being of epicardial mesothelial origin. When added to long-term primary cultures of adult ventricular myocytes, epicardial mesothelial cells appeared to induce myofibrillar arrays that were more organized than those seen in noncocultured myocytes; these changes that occurred were concurrent with the appearance of large amplitude contractions and multicellular synchronous beating that was facilitated by gap junctions between myocytes and epicardial mesothelial cells. The changes in morphology and function were accompanied by a marked increase in beta-myosin heavy chain isoform transcription in cocultured myocytes, a return to the ratio of cardiac to skeletal alpha-actin expected in adult rat myocardium, and a much reduced expression of smooth muscle alpha-actin. These changes in myocyte phenotype and function appeared to require epicardial cell-myocyte contact, or close apposition, because media conditioned by epicardial mesothelial cells alone or in coculture had no effect. Thus, these rapid and reversible changes in myocyte ultrastructure, function, and gene expression may provide a useful in vitro model with which to study the mechanism responsible for regulating the plasticity of ventricular myocyte phenotype and the role of specific cell-cell interactions.
Changes in intracellular free calcium concentration during long exposures to simulated ischemia in isolated mammalian ventricular muscle.
Authors: Lee J A , Allen D G
Published: June 2012

Intracellular free calcium concentration ([Ca2+]i) was measured in isolated ferret ventricular papillary muscles during and after long exposures to ischemia. All experiments were performed at 37 degrees C, and the muscles were stimulated at 1 Hz. Ischemia was simulated by changing from superfusion with oxygenated Tyrode's solution to superfusion with water-saturated gas (95% N2-5% CO2), thus simultaneously stopping oxygenation and restricting the extracellular space. [Ca2+]i was measured with aequorin, which was microinjected into superficial cells of the preparation. Exposure to ischemia caused a complex series of changes in [Ca2+]i. In the first few minutes the changes in [Ca2+]i were variable; however, after approximately 5 minutes all preparations exhibited a progressive increase in amplitude and duration of the stimulated rise in [Ca2+]i (the calcium transient). The amplitude of the calcium transients peaked after approximately 18 minutes of ischemia, when they were 339% of the control value. After this peak, the calcium transients progressively failed to occur in response to stimulation and declined in amplitude; simultaneously, spontaneous oscillations of [Ca2+]i appeared and increased in size and frequency. The oscillations in turn then gradually became less frequent until a large, prolonged (5-10 minute) increase in [Ca2+]i occurred, after which [Ca2+]i returned to a low level. There were no further oscillations after this event, which was seen on average after 37 minutes of ischemia. A slowly progressive contracture often began to develop at about this time. A gradual rise in resting [Ca2+]i occurred during the remainder of the exposure to ischemia. When muscles were reperfused after long exposures to ischemia, there was a very large and prolonged increase in [Ca2+]i, which was usually associated with a contracture and failure of recovery of developed tension. The large increase in [Ca2+]i could be reduced by the inclusion of 3 mM nickel chloride in the reperfusing solution. Comparison between reperfusion with O2 gas versus reperfusion with anoxic Tyrode's solution indicated that reoxygenation was more beneficial to the muscle than resumption of bulk flow. These results reveal the complex spectrum of changes in [Ca2+]i that occur during ischemia and on reperfusion. These changes in [Ca2+]i are likely to play an important role in the generation of ischemic arrhythmias and muscle damage.
Mechanisms of vasodilation induced by NKH477, a water-soluble forskolin derivative, in smooth muscle of the porcine coronary artery.
Authors: Shafiq J , Suzuki S , Itoh T , Kuriyama H
Published: June 2012

To study the mechanism of vasodilation induced by 6-(3-dimethylaminopropionyl) forskolin (NKH477), a water-soluble forskolin derivative, its effects on the acetylcholine (ACh)-induced contraction of muscle strips of porcine coronary artery were examined. [Ca2+]i, isometric force, and cellular concentrations of cAMP and inositol 1,4,5-trisphosphate were measured. NKH477 (0.1-1.0 microM), isoproterenol (0.01-0.1 microM), or forskolin (0.1-1.0 microM) increased cAMP and attenuated the contraction induced by 128 mM K+ or 10 microM ACh in a concentration-dependent manner. These agents, at concentrations up to 0.3 microM, did not change the amount of cGMP. NKH477 (0.1 microM) attenuated the contraction induced by 128 mM K+ without corresponding changes in the evoked [Ca2+]i responses. ACh (10 microM) produced a large phasic increase followed by a small tonic increase in [Ca2+]i and produced a sustained contraction. The ACh-induced phasic increase in [Ca2+]i, but not the tonic increase, disappeared after application of 0.1 microM ionomycin. NKH477 (0.1 microM) attenuated both the increase in [Ca2+]i and the force induced by 10 microM ACh in muscle strips that were not treated with ionomycin and inhibited the ACh-induced contraction without corresponding changes in [Ca2+]i in ionomycin-treated muscle strips. These results suggest that NKH477 inhibits ACh-induced Ca2+ mobilization through its action on ionomycin-sensitive storage sites. In ionomycin-treated and 128 mM K(+)-treated muscle strips, 0.1 microM NKH477 shifted the [Ca2+]i-force relation to the right in the presence or absence of 10 microM ACh. In beta-escin-skinned smooth muscle strips, 0.1 microM NKH477 shifted the pCa-force relation to the right but had no effects on Ca(2+)-independent contraction. We conclude that in smooth muscle of porcine coronary artery, NKH477 inhibits ACh-induced contraction by both attenuating ACh-induced Ca2+ mobilization and reducing the sensitivity of the contractile machinery to Ca2+, possibly by activating cAMP-dependent mechanisms.
Role of neutrophil adherence receptors (CD 18) in lung permeability following lower torso ischemia.
Authors: Welbourn R , Goldman G , Kobzik L , Paterson I S , Valeri C R , Shepro D , Hechtman H B
Published: June 2012

Ischemia and reperfusion of the lower torso lead to leukotriene- and neutrophil (PMN)-dependent lung injury characterized by lung PMN sequestration, increased permeability, and noncardiogenic edema. It is thought that PMNs require adhesion to endothelium to alter barrier function. This study tests the role of CD 18, the PMN adherence receptor, in mediating lung permeability after lower torso ischemia and reperfusion. Anesthetized rabbits (n = 9) underwent 3 hours of bilateral hind limb ischemia. Ten minutes after the release of the tourniquets, plasma leukotriene B4 levels increased to 395 +/- 85 pg/ml, higher than 129 +/- 35 pg/ml in controls (n = 9, p less than 0.01). At this time there was a reduction in circulating white blood cells (x 10(3)), 3.56 +/- 0.49/mm3 relative to 6.07 +/- 0.61/mm3 in controls (p less than 0.01). PMNs were sequestered in the hind limbs, indicated by increased myeloperoxidase activity of 1.06 +/- 0.19 units/g compared with 0.56 +/- 0.09 units/g in controls (p less than 0.05). Four hours after tourniquet release, PMNs were sequestered in the lungs, 52 +/- 4 PMNs per 10 high-power fields, a value higher than 31.5 +/- 3 PMNs per 10 high-power fields in controls; bronchoalveolar lavage fluid protein content increased to 554 +/- 90 micrograms/ml relative to 277 +/- 46 micrograms/ml in controls; and there was lung edema, measured by increased wet weight-to-dry weight ratios of 5.19 +/- 0.10, higher than 4.29 +/- 0.21 in controls (all p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Expression of A-, B-, and C-type natriuretic peptide genes in failing and developing human ventricles. Correlation with expression of the Ca(2+)-ATPase gene.
Authors: Takahashi T , Allen P D , Izumo S
Published: June 2012

Brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are novel natriuretic peptides, originally isolated from porcine brain. Similar to atrial natriuretic peptide (ANP), BNP is also synthesized in and secreted from cardiocytes, but CNP is not expressed at significant levels in normal adult myocardium. Previous studies have indicated that the serum level and ventricular expression of the ANP gene were augmented in patients with heart failure. Recently, the serum level of BNP was also reported to increase in human heart failure. To examine whether or not the expression of these natriuretic peptides is regulated in ventricular myocardium in a concordant manner, we performed Northern blot analysis using total cellular RNA isolated from the diseased left ventricles of 30 cardiac transplant recipients with end-stage heart failure, seven ventricles from organ donors (control group), and two ventricles of artificially aborted 17- and 19-week-old fetuses. The levels of mRNAs encoding both BNP and ANP increased significantly (p less than 0.01) in the left ventricular myocardium from the patients with end-stage heart failure as compared with the control group. The levels of BNP mRNA correlated positively with those of ANP mRNA (r = 0.73, p less than 0.01) and negatively with those of sarcoplasmic reticulum Ca(2+)-ATPase mRNA (r = -0.66, p less than 0.01) in the left ventricular myocardium from the patients with heart failure. There was also a negative correlation between the levels of ANP and the sarcoplasmic reticulum Ca(2+)-ATPase mRNAs (r = -0.65, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Acidic and basic fibroblast growth factors in adult rat heart myocytes. Localization, regulation in culture, and effects on DNA synthesis.
Authors: Speir E , Tanner V , Gonzalez A M , Farris J , Baird A , Casscells W
Published: June 2012

Basic fibroblast growth factor (bFGF) and acidic fibroblast growth factor (aFGF) are involved in the induction of embryonic mesoderm, angiogenesis, neuronal differentiation, and proliferation and survival of many cell types. In cardiac myocytes their roles are not well understood. Effects of fibroblast growth factors on reexpression of fetal actin genes have been reported. In freshly isolated adult rat cardiac myocytes, bFGF mRNA was not detectable by in situ hybridization, although the cells contained significant amounts of bFGF and aFGF as quantified by radioimmunoassays, mitogen assays with immunoneutralization, and Western blotting. After culturing, bFGF mRNA was detected (aFGF mRNA was not studied), and the cells contained 2.5-fold more bFGF and 60% more aFGF than freshly isolated cells. The FGFs were not found in conditioned medium. They were localized, especially in cultured cells, to the nucleus. Cultured myocytes bound fourfold more 125I-FGF than freshly isolated cells and expressed the fibroblast growth factor R-1 (flg) gene. The addition of bFGF or aFGF in serum-free medium to pure populations of myocytes (after 10 days in culture, at which time they are spread, beating, and multinucleated) led to increased thymidine incorporation. Expression of fibroblast growth factors and fibroblast growth factor receptors by adult cardiac myocytes that survive the shock and "dedifferentiation" of culturing may contribute to DNA synthesis and, by analogy, to other cell types, to regulation of ribosomal and actin genes, and to cell survival. These possibilities and their in vivo relevance will require further study.
Reflection after delayed excitation in a computer model of a single fiber.
Authors: Cabo C , Barr R C
Published: June 2012

Reflection (reflected reentry) is a case of reentry in a one-dimensional structure, divided into proximal and distal segments, in which tissue excited by a wave front propagating in a forward direction is reexcited by electrical activity coming backward from the original direction of propagation. Cases of reflection have been demonstrated in Purkinje fibers and in ventricular muscle preparations containing multiple fibers. Several mechanisms possibly responsible for reflected reentry have been proposed. However, the difficulty in the interpretation of the experimental results, as well as the limited number of different conditions in which reflection was obtained, has kept open the question about conditions and mechanisms for reflection. We have developed a computer model in which reflection occurs. The model involves a single fiber and uses the DiFrancesco-Noble equations for the Purkinje fiber to model the ionic currents. The results show that reflection is possible in a single fiber and that diastolic depolarization (automaticity) is not a requirement for reflection. Active membrane responses to a just-above-threshold stimulus were important for achieving the necessary time delay. Systematic simulations showed further that reflection occurred only when the right coupling conditions linked a short or long proximal fiber to a short distal segment.
Endogenous calcitonin gene-related peptide mediates nonadrenergic noncholinergic depressor response to spinal cord stimulation in the pithed rat.
Authors: Taguchi T , Kawasaki H , Imamura T , Takasaki K
Published: June 2012

The role of endogenous calcitonin gene-related peptide (CGRP) in the nonadrenergic noncholinergic depressor response to spinal cord stimulation was studied in the pithed rat in vivo. Pithed rats were given hexamethonium (2 mg/kg per minute i.v.) to block autonomic outflow, and mean blood pressure was artificially maintained at approximately 100 mm Hg with methoxamine (10-15 micrograms/kg per minute i.v.). Electrical stimulation of the spinal cord at the level of the lower thoracic vertebra (T9-12) caused a fall in blood pressure in a frequency-dependent (0.5-10 Hz), voltage-dependent (2.5-50 V), and pulse duration-dependent (0.25-8 msec) manner. The heart rate did not change during the depressor response. The depressor response was long lasting, and the maximum response was elicited by stimulation at 4-6 Hz. The neurotoxin tetrodotoxin (100 micrograms/kg i.v.) abolished the depressor response to spinal cord stimulation, whereas treatment with propranolol (0.5 mg/kg per minute i.v.), atropine (0.05 mg/kg per minute i.v.), or a combination of pyrilamine (0.5 mg/kg per minute i.v.) and cimetidine (0.5 mg/kg per minute i.v.) did not affect the response. In pithed rats treated with capsaicin (total dose of 500 mg/kg s.c.), spinal cord stimulation caused a slight depressor response. Exogenous CGRP, but not acetylcholine, isoproterenol, histamine, or substance P, caused a sustained fall in blood pressure that mimicked the spinal cord stimulation-induced depressor response. Continuous infusion of CGRP[8-37] (60 nmol/kg per minute i.v.), a CGRP receptor antagonist, markedly inhibited the depressor responses not only to spinal cord stimulation but also to exogenous CGRP.(ABSTRACT TRUNCATED AT 250 WORDS)
Basal metabolism adds a significant offset to unloaded myocardial oxygen consumption per minute.
Authors: Harasawa Y , de Tombe P P , Sheriff D D , Hunter W C
Published: June 2012

Myocardial oxygen consumption (MVO2) includes components for 1) mechanical energy generation, 2) activation, and 3) basal metabolism. Whereas the first two components are expected to increase in proportion with heart rate, a significant basal level of metabolism would consume oxygen even if the heart rate were zero. Contrary to this expectation, however, a previous study reported that, during unloaded beats, MVO2 per beat (which includes basal metabolism) was independent of heart rate. Accordingly, unloaded MVO2 per minute would extrapolate to zero at zero heart rate; this result is unexpected considering basal metabolism. To resolve this inconsistency, we varied heart rate over a wide range after inducing atrioventricular block in eight isolated cross-circulated canine hearts that contracted isovolumically. We examined whether a term representing rate-independent basal metabolism was needed to describe MVO2 per minute. Mechanical energy generated by the left ventricle was evaluated from the pressure-volume area, which was altered by changing isovolumic ventricular volume over at least five levels at each heart rate. Contractility, evaluated by the slope of the end-systolic pressure-volume relation, did not vary significantly with heart rate in this study. In contrast to the previous report, unloaded MVO2 per beat (i.e., MVO2 extrapolated to a pressure-volume area of zero) was not constant but fell monotonically with increases in heart rate in every heart. We considered that this trend was caused by a significant rate-independent basal level of MVO2 per minute. Multiple linear regression analysis confirmed that this rate-independent basal term differed significantly from zero in seven of the eight hearts studied.(ABSTRACT TRUNCATED AT 250 WORDS)
A model study of volume conductor effects on endocardial and intracavitary potentials.
Authors: Khoury D S , Rudy Y
Published: June 2012

An idealized mathematical model was developed to study the effects of variations in conductive and geometric parameters on measured endocardial and intracavitary potentials. The model consists of a spherical multielectrode probe located eccentrically within a system of concentric spheres that represent a blood cavity, myocardium, lung region, and surface muscle layer. Solutions were found for endocardial and intracavitary probe potentials produced by two different configurations of equivalent myocardial sources: 1) multiple activation wave fronts oriented radially, representing global fronts in the myocardium; and 2) pairs of equal and opposite dipoles on a line oriented tangentially to the endocardial surface, representing cardiac sources during early ectopic activation. It was found that the complexities of the cardiac source configurations are reflected in the endocardial potential but not in the associated probe potential, which exhibits a smoothed-out, low-amplitude distribution. In addition, probe potential depends on probe size and location within the cavity. Furthermore, endocardial and probe potentials are influenced by variations in the conductivity of different regions; an increase in blood conductivity results in a decrease in both endocardial and probe potential magnitudes produced by either type of cardiac sources, and an increase in myocardial conductivity results in an increase in both potential magnitudes, whereas an increase in lung conductivity results in an increase in the magnitude of the potential produced by radial sources but a small decrease in the magnitude of the potential produced by tangential sources. The effects of variations in skeletal muscle conductivity are negligible. The volume conductor effects of myocardial anisotropy (9:1 anisotropy ratio) are to attenuate both endocardial and probe potentials by as much as 60% and 71%, respectively, for radial sources and by 96% and 85%, respectively, for tangential sources. In conclusion, volume conductor influences should be considered in the interpretation of measured cavity potentials. Multiple myocardial events are resolved in endocardial potentials but not in potentials measured by an intracavitary multielectrode probe. This observation indicates that for the purpose of resolving cardiac activity, efforts should be directed at inverse reconstruction of endocardial potentials from potentials measured with an intracavitary probe.
Dependence of hypoxic cellular calcium loading on Na(+)-Ca2+ exchange.
Authors: Haigney M C , Miyata H , Lakatta E G , Stern M D , Silverman H S
Published: June 2012

Na(+)-Ca2+ exchange has been shown to contribute to reperfusion- and reoxygenation-induced cellular Ca2+ loading and damage in the heart. Despite the fact that both [Na+]i and [Ca2+]i have been documented to rise during ischemia and hypoxia, it remains unclear whether the rise in [Ca2+]i occurring during hypoxia is linked to the rise in [Na+]i via Na(+)-Ca2+ exchange before reoxygenation and how this relates to cellular injury. Single electrically stimulated (0.2 Hz) adult rat cardiac myocytes loaded with Na(+)-sensitive benzofuran isophthalate (SBFI), the new fluorescent probe, were exposed to glucose-free hypoxia (PO2 less than 0.02 mm Hg), and SBFI fluorescence was monitored to index changes in [Na+]i. Parallel experiments were performed with indo-1-loaded cells to index [Ca2+]i. The SBFI fluorescence ratio (excitation, 350/380 nm) rose significantly during hypoxia after the onset of ATP-depletion contracture, consistent with a rise in [Na+]i. At reoxygenation, the ratio fell rapidly toward baseline levels. The indo-1 fluorescence ratio (emission, 410/490 nm) also rose only after the onset of rigor contracture and then often showed a secondary rise early after reoxygenation at a time when [Na+]i fell. The increase in both [Na+]i and [Ca2+]i, seen during hypoxia, could be markedly reduced by performing experiments in Na(+)-free buffer. These experiments suggested that hypoxic Ca2+ loading is linked to a rise in Na+i via Na(+)-Ca2+ exchange. To show that Na(+)-Ca2+ exchange activity was not fully inhibited by profound intracellular ATP depletion, cells were exposed to cyanide, and then buffer Na+ was abruptly removed after contracture occurred. The sudden removal of buffer Na+ would be expected to stimulate cell Ca2+ entry via Na(+)-Ca2+ exchange. A large rapid rise in the indo-1 fluorescence ratio ensued, which was consistent with abrupt cell Ca2+ loading via the exchanger. The effect of reducing hypoxic buffer [Na+] on cell morphology after reoxygenation was examined. Ninety-five percent of cells studied in a normal Na(+)-containing buffer (144 mM NaCl, n = 38) and reoxygenated 30 minutes after the onset of hypoxic rigor underwent hypercontracture. Only 12% of cells studied in Na(+)-free buffer (144 mM choline chloride, n = 17) hypercontracted at reoxygenation (p less than 0.05). Myocytes were also exposed to hypoxia in the presence of R 56865, a compound that blocks noninactivating components of the Na+ current. R 56865 blunted the rise in [Na+]i typically seen after the onset of rigor, suggesting that Na+ entry may occur, in part, through voltage-gated Na+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
Suppression of endothelin-1 secretion by lysophosphatidylcholine in oxidized low density lipoprotein in cultured vascular endothelial cells.
Authors: Jougasaki M , Kugiyama K , Saito Y , Nakao K , Imura H , Yasue H
Published: June 2012

Oxidatively modified low density lipoprotein (oxidized LDL), an atherogenic lipoprotein that exists in the atherosclerotic arteries, has been shown to alter endothelial cell functions. In the present study, we examined the effects of oxidized LDL on the production of endothelin-1-like immunoreactivity (ET-1-LI) by the cultured vascular endothelial cells from porcine aorta and human umbilical vein. Incubation with oxidized LDL resulted in a dose-dependent suppression of ET-1-LI release by both endothelial cells. Oxidized LDL also inhibited thrombin-mediated stimulation of ET-1-LI secretion. However, native LDL had no effects on ET-1-LI secretion. A lipid extract from oxidized LDL, but not from native LDL, inhibited ET-1-LI secretion, indicating that the lipid component of oxidized LDL was required for the inhibition of ET-1-LI secretion. Oxidative modification of LDL was associated with degradation of a substantial amount of phosphatidylcholine to lysophosphatidylcholine (LPC). Pretreatment with defatted albumin, which is an acceptor for hydrophilic lipids including LPC, reduced LPC concentration in oxidized LDL to that in native LDL and simultaneously prevented the inhibitory effects of oxidized LDL on ET-1-LI secretion. Incubation with synthetic LPC (palmitoyl), but not with synthetic phosphatidylcholine (dipalmitoyl), suppressed ET-1-LI secretion by the endothelial cells. No cell death was observed during the incubations as judged by the trypan blue exclusion test, and protein synthesis of the endothelial cells was not affected by lipids or lipoproteins at a concentration at which suppression of ET-1-LI was observed. We concluded that LPC in oxidized LDL causes suppression of ET-1-LI release, which may counteract the vasoconstrictive properties of atherosclerotic arteries.
Cod liver oil alters platelet-arterial wall response to injury in pigs.
Authors: Lam J Y , Badimon J J , Ellefson R D , Fuster V , Chesebro J H
Published: June 2012

In 36 normolipemic pigs randomized to a 4-week feeding with regular pig chow (n = 18, control group) or chow supplemented with cod liver oil (1 ml/kg per day) (n = 18, treated group), treatment with cod liver oil produced a significant decrease in serum cholesterol, low density lipoprotein cholesterol, and triglycerides. Deep carotid arterial wall injury (media exposed) by balloon angioplasty was associated with less 111In-labeled platelet deposition (24.6 +/- 4.8 x 10(6)/cm2 versus 62.5 +/- 17.0 x 10(6)/cm2, p less than 0.05; difference, -33.8 x 10(6)/cm2; 95% confidence interval [CI], -1.9 x 10(6)/cm2 to -73.9 x 10(6)/cm2) and injury-related vasoconstriction (21.3 +/- 2.2% versus 30.9 +/- 2.9%, p less than 0.05; difference, -9.6%; 95% CI, -2.2% to -17.0%) in the cod liver oil-treated group than in the control group; with mild injury (media not exposed), platelet deposition was low and unchanged (6.2 +/- 0.5 x 10(6)/cm2 versus 7.8 +/- 0.7 x 10(6)/cm2; difference, -1.6 x 10(6)/cm2; 95% CI, -1.1 x 10(6)/cm2 to +4.3 x 10(6)/cm2), but associated vasoconstriction was reduced respectively (16.3 +/- 2.0% versus 23.0 +/- 2.2%, p less than 0.05; difference, -6.7%; 95% CI, -0.6% to -12.8%). When arterial blood from cod liver oil-treated pigs superfused normal aortic media ex vivo, platelet deposition onto the normal aortic media was lower than when arterial blood from control pigs superfused the normal aortic media (43.7 +/- 8.8 x 10(6)/cm2 versus 66.8 +/- 13.0 x 10(6)/cm2, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects on the rabbit coronary artery of LP-805, a new type of releaser of endothelium-derived relaxing factor and a K+ channel opener.
Authors: Nakashima M , Akata T , Kuriyama H
Published: June 2012

In the rabbit epicardial coronary artery, 8-tert-butyl-6,7-dihydropyrolo[3,2-e]5-methylpyrazolo [1,5-a]pyrimidine-3-carbonitrile (LP-805, greater than 0.1 microM) hyperpolarized the muscle membrane in both proximal (diameter, 1-1.2 mm) and distal (diameter, 0.1-0.2 mm) regions of intact (+E) tissue, in which endothelium is present, and endothelium-denuded (-E) tissue. LP-805-induced hyperpolarization was inhibited by glibenclamide. In -E tissues in both regions, acetylcholine (ACh, greater than 0.1 microM) depolarized the membrane, and LP-805 inhibited the depolarization. However, in +E tissues, ACh (greater than 0.1 microM) transiently hyperpolarized the membrane that was not modified by glibenclamide (10 microM), charybdotoxin (100 nM), and NG-nitro-L-arginine (L-NNA, 100 microM). In -E tissues of both regions, LP-805 consistently inhibited the 10 microM ACh-induced contraction (IC50, 2.8 microM), and 10 microM glibenclamide shifted this concentration-response curve to the right (IC50, 20 microM). In +E tissues, LP-805 more potently inhibited the ACh-induced contraction (IC50, 0.3 microM), and this inhibition was prevented by L-NNA (100 microM) but not by indomethacin or glibenclamide (10 microM). In -E and +E tissues of both regions, LP-805 repolarized the high K(+)-induced depolarization (less than 20 mM) and relaxed the tissues precontracted by high K+ (less than 30 mM); these electrical and mechanical effects of LP-805 were prevented by glibenclamide (10 microM) in +E tissues. In +E tissues, the K(+)-induced contraction (less than 30 mM) was more strongly inhibited than in -E tissues, but after treatment with L-NNA, LP-805 relaxed -E and +E tissues precontracted to the same extent in the presence of high K+. LP-805 (10 microM) did not inhibit the Ca(2+)-induced contraction in skinned muscle tissues but did slightly inhibit the ACh-induced contraction in Ca(2+)-free solution containing 2 mM EGTA. Thus, LP-805 has a potent releasing action on endothelium-derived relaxing factor and also the potential to open the glibenclamide-sensitive K+ channel. These events would account for the dilation of the rabbit coronary artery exposed to LP-805.
Different effects of alpha- and beta-adrenergic stimulation on cytosolic pH and myofilament responsiveness to Ca2+ in cardiac myocytes.
Authors: Gambassi G , Spurgeon H A , Lakatta E G , Blank P S , Capogrossi M C
Published: June 2012

alpha-Adrenergic stimulation (alpha-AS) and beta-adrenergic stimulation (beta-AS) of the myocardium are associated respectively with an increase and a decrease in myofilament responsiveness to Ca2+. We hypothesized that changes in cytosolic pH (pH(i)) may modulate these opposite actions of alpha-AS and beta-AS. The effects of alpha-AS (50 microM phenylephrine and 1 microM nadolol) and beta-AS (0.05 microM isoproterenol) on contraction and either cytosolic Ca2+ (Cai) or pH(i) were assessed in adult rat ventricular myocytes bathed in bicarbonate buffer (pH 7.36 +/- 0.05). In cells loaded with the ester derivative (AM form) of indo-1, the 410/490-nm ratio of emitted fluorescence indexed Cai. Myofilament responsiveness to Ca2+ was assessed by the relaxation phase of the length-indo-1 fluorescence relation during a twitch. alpha-AS and beta-AS shifted this relation in opposite directions, indicating that alpha-AS increased and beta-AS decreased myofilament responsiveness to Ca2+. In addition, the positive inotropic action of alpha-AS was associated with an increased Cai transient amplitude in 50% of the myocytes (n = 12), whereas beta-AS always increased Cai (n = 5). In cells loaded with the fluorescent pH(i) probe SNARF-1 AM, the emitted 590/640-nm fluorescence is a measure of pH(i). The effect of alpha-AS on the extent of cell shortening during the twitch (ES) was expressed as the percentage of resting cell length. Both ES and pH(i) were assessed in myocytes bathed in 1.5 mM [Ca2+] and stimulated at 0.5 Hz (control ES, 7.4 +/- 1.5%; control pH(i), 7.11 +/- 0.05; n = 10). alpha-AS enhanced both ES (delta ES, 1.8 +/- 0.6%; p less than 0.05) and pH(i) (delta pH(i), 0.06 +/- 0.01; p less than 0.005), and there was a significant correlation between delta ES and delta pH(i) (r = 0.76, p less than 0.05). A similar effect of alpha-AS on pH(i) was observed in the absence of electrical stimulation (n = 8). The alpha-AS-induced enhancement of ES and pH(i) was abolished by 10 microM ethylisopropylamiloride, a Na(+)-H+ exchange inhibitor (n = 7). In additional experiments, myocytes were preincubated either with 0.2 microM 4 beta-phorbol 12-myristate 13-acetate (n = 8) or with 5 nM staurosporine (n = 8), which have been shown to downregulate and inhibit Ca(2+)-activated phospholipid-dependent protein kinase C, respectively. In either group, alpha-AS had no effect on pH(i) and decreased ES to approximately 60% of control.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of brief myocardial ischemia on sympathetic coronary vasoconstriction.
Authors: Gutterman D D , Morgan D A , Miller F J
Published: June 2012

The purpose of the present study was to determine whether sympathetic coronary vasoconstrictor responses are altered after brief ischemia and reperfusion. Adult mongrel dogs were anesthetized and instrumented for measurements of heart rate, arterial pressure, left ventricular pressure, left ventricular dP/dt, anterior myocardial wall thickening, and left circumflex coronary artery (LCX) and left anterior descending coronary artery (LAD) blood flow velocities. Changes in coronary vascular resistance were recorded during intravenous bolus doses of norepinephrine and bilateral electrical stimulation of the stellate ganglia. After beta-adrenergic blockade and bilateral vagotomy, electrical stimulation of the stellate ganglia increased coronary vascular resistance in the LAD and LCX beds by 38 +/- 5% and 39 +/- 5%, respectively. After a 15-minute LAD occlusion, repeat electrical stimulation produced increases in coronary resistance of 16 +/- 3% and 45 +/- 8%, respectively (p less than 0.05 for the LAD before versus after the occlusion). The peak increase in coronary vascular resistance to two doses of norepinephrine was unchanged. After a shorter period of myocardial ischemia (7 minutes), similar increase in coronary resistance to stellate stimulation were observed before (27 +/- 4%) and after (26 +/- 6%) myocardial ischemia. The mechanism of this impaired sympathetic coronary vasoconstriction was further tested by examining the responses to bretylium and tyramine. Brief ischemia did not alter the coronary constrictor responses to either bretylium or tyramine, suggesting that mechanisms governing prejunctional release of norepinephrine are intact in the postischemic coronary arterial bed.(ABSTRACT TRUNCATED AT 250 WORDS)