bluuebunny/crossref_metadata_2025 huggingface dataset:
Triggered activity due to delayed afterdepolarizations in sites of focal origin of ischemic ventricular tachycardia
Authors: Xing Dezhi , Martins James B.
Published: October 2004

This study for the first time systematically evaluated the site of origin of focal ventricular tachycardia (VT) induced 1–3 h after acute coronary artery ligation in dogs. We determined whether delayed afterdepolarizations (DADs) and triggered activity (TA) are more often recorded from ischemic endocardium excised from focal sites of VT origin. A total of 145 α-chloralose-anesthetized dogs were studied: in 54 dogs without inducible VT, normal or ischemic endocardium was investigated in vitro; in 91 dogs, inducible VT was studied by three-dimensional activation mapping, with in vitro study of 51 endocardial foci compared with 40 endocardial ischemic sites not of VT origin. Incidence of DADs (71% vs. 33%, P < 0.05) and TA (32% vs. 11%, P < 0.05) was greater in ischemic than in normal Purkinje tissues. Purkinje sites of origin of focal VT demonstrated the greatest frequency of DADs (92%, P < 0.05) and TA (75%, P < 0.05), with repetitive TA predominating. Similar results were obtained in endocardial sites of origin. Action potentials were mildly depolarized and prolonged in the focal sites of origin. These abnormalities were stable up to 2.5 h of recording. This study demonstrated that DADs and TA may underlie a majority of focal VTs in ischemic endocardium and Purkinje tissue.
Mechanosensitive cardiac C-fiber response to changes in left ventricular filling, coronary perfusion pressure, hemorrhage, and volume expansion in rats
Authors: Ditting Tilmann , Hilgers Karl F. , Scrogin Karie E. , Stetter Alexander , Linz Peter , Veelken Roland
Published: October 2004

Left ventricular (LV) end-diastolic pressure (LVEDP) increase due to volume expansion (VExp) enhances mechanosensitive vagal cardiac afferent C-fiber activity (CNFA), thus decreasing renal sympathetic nerve activity (RSNA). Hypotensive hemorrhage (hHem) attenuates RSNA despite decreased LVEDP. We hypothesized that CNFA increases with any change in LVEDP. Coronary perfusion pressure (CPP), supposedly affected in both conditions, might also be a stimulus of CNFA. VExp and hHem were performed in anesthetized male Sprague-Dawley rats while blood pressure, heart rate, and RSNA were measured. Cervical vagotomy abolished RSNA response in both reflex responses. Single-unit CNFA was recorded while LVEDP was changed. Rapid changes (± 4, ±6, ±8 mmHg) were obtained by graded occlusion of the caval vein and descending aorta. Prolonged changes were obtained by VExp and hHem. Furthermore, CNFA was recorded in a modified Langendorff heart while CPP was changed (70, 100, 40 mmHg). Rapid LVEDP changes increased CNFA [caval vein occlusion: +16 ± 3 Hz (approximately +602%); aortic occlusion: +15 ± 3 Hz (approximately +553%); 70 units; P < 0.05]. VExp and hHem ( n = 6) increased CNFA [VExp: +10 ± 4 Hz (approximately +1,033%); hHem: +10 ± 2 Hz (approximately +1,225%); P < 0.05]. An increase in CPP increased CNFA [+2 ± 1 Hz (approximately +225%); P < 0.05], whereas a decrease in CPP decreased CNFA [−0.8 ± 0.4 Hz (approximately −50%); P < 0.05]. All C fibers recorded originated from the LV. CNFA increased with any LVEDP change but changed equidirectionally with CPP. Thus neither LVEDP nor CPP fully accounts directly for afferent C-fiber and reflex sympathetic responses. The intrinsic afferent stimuli and receptive fields accounting for reflex sympathoinhibition still remain cryptic.
Endostatin uncouples NO and Ca2+response to bradykinin through enhanced O2−· production in the intact coronary endothelium
Authors: Zhang Andrew Y. , Teggatz Eric G. , Zou Ai-Ping , Campbell William B. , Li Pin-Lan
Published: October 2004

The present study tested the hypothesis that endostatin stimulates superoxide (O2−·) production through a ceramide-mediating signaling pathway and thereby results in an uncoupling of bradykinin (BK)-induced increases in intracellular Ca2+concentration ([Ca2+]i) from nitric oxide (NO) production in coronary endothelial cells. With the use of high-speed, wavelength-switching, fluorescence-imaging techniques, the [Ca2+]iand NO levels were simultaneously monitored in the intact endothelium of freshly isolated bovine coronary arteries. Under control conditions, BK was found to increase NO production and [Ca2+]iin parallel. When the arteries were pretreated with 100 nM human recombinant endostatin for 1 h, this BK-induced NO production was reduced by 89%, whereas [Ca2+]iwas unchanged. With the conversion rate of l-[3H]arginine to l-[3H]citrulline measured, endostatin had no effect on endothelial NO synthase (NOS) activity, but it stimulated ceramide by activation of sphingomyelinase (SMase), whereby O2−· production was enhanced in endothelial cells. O2−· scavenging by tiron and inhibition of NAD(P)H oxidase by apocynin markedly reversed the effect of endostatin on the NO response to BK. These results indicate that endostatin increases intracellular ceramide levels, which enhances O2−· production through activation of NAD(P)H oxidase. This ceramide-O2−· signaling pathway may contribute importantly to endostatin-induced endothelial dysfunction.
RhoA GTPase regulates L-type Ca2+currents in cardiac myocytes
Authors: Yatani Atsuko , Irie Keiichi , Otani Takayuki , Abdellatif Maha , Wei Lei
Published: October 2004

Regulation of ionic channels plays a pivotal role in controlling cardiac function. Here we show that the Rho family of small G proteins regulates L-type Ca2+currents in ventricular cardiomyocytes. Ventricular myocytes isolated from transgenic (TG) mice that overexpress the specific GDP dissociation inhibitor Rho GDI-α exhibited significantly decreased basal L-type Ca2+current density (∼40%) compared with myocytes from nontransgenic (NTG) mice. The Ca2+channel agonist BAY K 8644 and the β-adrenergic agonist isoproterenol increased Ca2+currents in both NTG and TG myocytes to a similar maximal level, and no changes in mRNA or protein levels were observed in the Ca2+channel α1-subunits. These results suggest that the channel activity but not the expression level was altered in TG myocytes. In addition, the densities of inward rectifier and transient outward K+currents were unchanged in TG myocytes. The amplitudes and rates of basal twitches and Ca2+transients were also similar between the two groups. When the protein was delivered directly into adult ventricular myocytes via TAT-mediated protein transduction, Rho GDI-α significantly decreased Ca2+current density, which supports the idea that the defective Ca2+channel activity in TG myocytes was a primary effect of the transgene. In addition, expression of a dominant-negative RhoA but not a dominant-negative Rac-1 or Cdc42 also significantly decreased Ca2+current density, which indicates that inhibition of Ca2+channel activity by overexpression of Rho GDI-α is mediated by inhibition of RhoA. This study points to the L-type Ca2+channel activity as a novel downstream target of the RhoA signaling pathway.
Muscle mechanoreceptor sensitivity in heart failure
Authors: Middlekauff Holly R. , Chiu Josephine , Hamilton Michele A. , Fonarow Gregg C. , MacLellan W. Robb , Hage Antoine , Moriguchi Jaime , Patel Jignash
Published: October 2004

Prior work in animals suggests that muscle mechanoreceptor control of sympathetic activation (MSNA) during exercise in heart failure (HF) is heightened and that muscle mechanoreceptors are sensitized by metabolic by-products. We sought to determine whether 1) muscle mechanoreceptor control of MSNA is enhanced in HF patients and 2) lactic acid sensitizes muscle mechanoreceptors during rhythmic handgrip (RHG) exercise in healthy humans and patients with HF. Dichloroacetate (DCA), which reduces the production of lactic acid, or saline control was infused in 12 patients with HF and 13 controls during RHG. MSNA was recorded (microneurography). After saline was administered and during exercise thereafter, MSNA increased earlier in HF compared with controls, consistent with baseline-heightened mechanoreceptor sensitivity. In both HF and controls, MSNA increased during the 3-min exercise protocol, consistent with further sensitization of muscle mechanoreceptors by metabolic by-product(s). During posthandgrip circulatory arrest, MSNA returned rapidly to baseline levels, excluding the muscle metaboreceptors as mediators of the sympathetic excitation during RHG. To isolate muscle mechanoreceptors from central command, we utilized passive exercise in 8 HF and 11 controls, and MSNA was recorded. MSNA increased significantly during passive exercise in HF but not in controls. In conclusion, muscle mechanoreceptors mediate the increase in MSNA during low-level RHG exercise in healthy humans, and this muscle mechanoreceptor control is augmented further in HF. Neither lactate generation nor the fall in pH during RHG plays a central role in muscle mechanoreceptor sensitization. Finally, muscle mechanoreceptors in patients with HF have heightened basal sensitivity to mechanical stimuli resulting in exaggerated early increases in MSNA.
Endothelin in the splanchnic vascular bed of DOCA-salt hypertensive rats
Authors: Wang Hong , Chen Alex F. , Watts Stephanie W. , Galligan James J. , Fink Gregory D.
Published: October 2004

Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETBreceptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETBreceptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETBreceptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.
Validation of echocardiographic methods for assessing left ventricular dysfunction in rats with myocardial infarction
Authors: Morgan Eric E. , Faulx Michael D. , McElfresh Tracy A. , Kung Theodore A. , Zawaneh Michael S. , Stanley William C. , Chandler Margaret P. , Hoit Brian D.
Published: October 2004

The rat infarct model is widely used in heart failure research, but few echocardiographic indexes of left ventricular (LV) function are validated in this model. Accordingly, the objective of this study was to validate a 13-segment LV wall motion score index (WMSI) and the myocardial performance index (MPI) in infarcted rats. Twenty-nine male Wistar rats underwent left coronary artery ligation or sham operation and were evaluated with two-dimensional and Doppler flow echocardiography 8 wk later. After echocardiography, invasive indexes were obtained using a high-fidelity catheter. WMSI and MPI were correlated with the invasive and noninvasive measurements of LV function. WMSI and MPI significantly correlated directly with end-diastolic pressure ( r = 0.72 and 0.42 for WMSI and MPI, respectively) and the time constant of isovolumic relaxation ( r = 0.68 and 0.48) and inversely with peak rate of rise of LV pressure (+dP/d t; r = −0.68 and −0.50), peak rate of decline in LV pressure ( r = −0.57 and −0.44), LV developed pressure ( r = −0.58 and −0.42), area fractional shortening ( r = −0.85 and −0.53), and cardiac index ( r = −0.74 and −0.74). Stepwise linear regression analyses revealed that LV end-diastolic pressure, +dP/d t, area fractional shortening, and cardiac index were independent determinants of WMSI ( r = 0.994) and that cardiac index and +dP/d t were independent determinants of MPI ( r = 0.781). We conclude that the 13-segment WMSI and MPI are reproducible and correlate strongly with established echocardiographic and invasive indexes of systolic and diastolic function. These findings support the use of WMSI and MPI as indexes of global LV function in the rat infarction model of heart failure.
Impact of β-myosin heavy chain isoform expression on cross-bridge cycling kinetics
Authors: Rundell Veronica L. M. , Manaves Vlasios , Martin Anne F. , de Tombe Pieter P.
Published: October 2004

Myosin heavy chain (MHC) isoforms α and β have intrinsically different ATP hydrolysis activities (ATPase) and therefore cross-bridge cycling rates in solution. There is considerable evidence of altered MHC expression in rodent cardiac disease models; however, the effect of incremental β-MHC expression over a wide range on the rate of high-strain, isometric cross-bridge cycling is yet to be ascertained. We treated male rats with 6-propyl-2-thiouracil (PTU; 0.8 g/l in drinking water) for short intervals (6, 11, 16, and 21 days) to generate cardiac MHC patterns in transition from predominantly α-MHC to predominantly β-MHC. Steady-state calcium-dependent tension development and tension-dependent ATP consumption (tension cost; proportional to cross-bridge cycling) were measured in chemically permeabilized (skinned) right ventricular muscles at 20°C. To assess dynamic cross-bridge cycling kinetics, the rate of force redevelopment ( ktr) was determined after rapid release-restretch of fully activated muscles. MHC isoform content in each experimental muscle was measured by SDS-PAGE and densitometry. α-MHC content decreased significantly and progressively with length of PTU treatment [68 ± 5%, 58 ± 4%, 37 ± 4%, and 27 ± 6% for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Tension cost decreased, linearly, with decreased α-MHC content [6.7 ± 0.4, 5.6 ± 0.5, 4.0 ± 0.4, and 3.9 ± 0.3 ATPase/tension for 6, 11, 16, and 21 days, respectively; P < 0.001 (ANOVA)]. Likewise, ktrwas significantly and progressively depressed with length of PTU treatment [11.1 ± 0.6, 9.1 ± 0.5, 8.2 ± 0.7, and 6.2 ± 0.3 s−1for 6, 11, 16, and 21 days, respectively; P < 0.05 (ANOVA)] Thus cross-bridge cycling, under high strain, for α-MHC is three times higher than for β-MHC. Furthermore, under isometric conditions, α-MHC and β-MHC cross bridges hydrolyze ATP independently of one another.
Exogenous NO suppresses flow-induced endothelium-derived NO production because of depletion of tetrahydrobiopterin
Authors: Mochizuki Seiichi , Sipkema Pieter , Goto Masami , Hiramatsu Osamu , Nakamoto Hiroshi , Toyota Eiji , Kajita Tatsuya , Shigeto Fumiyuki , Yada Toyotaka , Ogasawara Yasuo , Kajiya Fumihiko
Published: October 2004

Exogenous nitric oxide (NO) suppresses endothelium-derived NO production. We were interested in determining whether this is also the case in flow-induced endothelium-derived NO production. If so, then is the mechanism because of intracellular depletion of tetrahydrobiopterin [BH4; a cofactor of NO synthase (NOS)], which results in superoxide production by uncoupled NOS? Isolated canine femoral arteries were perfused with 100 μM S-nitroso- N-acetylpenicillamine (SNAP; an NO donor) and/or 64 μM BH4. Perfusion of SNAP suppressed flow-induced NO production, which was evaluated as a change in the slope of the linear relationship between perfusion rate and NO production rate ( P < 0.02 vs. control; n = 7). Subsequent BH4perfusion returned the slope to the control level. Concomitant perfusion of SNAP and BH4retained the control-level NO production ( n = 7). Concomitant perfusion of SNAP and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; 1 mM; a membrane-permeable superoxide scavenger) also retained the control-level NO production ( n = 7), whereas perfusion of Tiron after SNAP could not return the NO production to the control level ( P < 0.02 vs. control; n = 7). We also found a significant decrease in BH4concentration in the endothelial cells after SNAP perfusion. In conclusion, these results indicate that exogenous NO suppresses the flow-induced, endothelium-derived NO production by superoxide released from uncoupled NOS because of intracellular BH4depletion.
Feedback effects of circulating norepinephrine on sympathetic outflow in healthy subjects
Authors: Tulppo Mikko P. , Huikuri Heikki V. , Tutungi Elli , Kimmerly Derek S. , Gelb Adrian W. , Hughson Richard L. , Mäkikallio Timo H. , Shoemaker J. Kevin
Published: October 2004

The amplitude of low-frequency (LF) oscillations of heart rate (HR) usually reflects the magnitude of sympathetic activity, but during some conditions, e.g., physical exercise, high sympathetic activity results in a paradoxical decrease of LF oscillations of HR. We tested the hypothesis that this phenomenon may result from a feedback inhibition of sympathetic outflow caused by circulating norepinephrine (NE). A physiological dose of NE (100 ng·kg−1·min−1) was infused into eight healthy subjects, and infusion was continued after α-adrenergic blockade [with phentolamine (Phe)]. Muscle sympathetic nervous activity (MSNA) from the peroneal nerve, LF (0.04–0.15 Hz) and high frequency (HF; 0.15–0.40 Hz) spectral components of HR variability, and systolic blood pressure variability were analyzed at baseline, during NE infusion, and during NE infusion after Phe administration. The NE infusion increased the mean blood pressure and decreased the average HR ( P < 0.01 for both). MSNA (10 ± 2 vs. 2 ± 1 bursts/min, P < 0.01), LF oscillations of HR (43 ± 13 vs. 35 ± 13 normalized units, P < 0.05), and systolic blood pressure (3.1 ± 2.3 vs. 2.0 ± 1.1 mmHg2, P < 0.05) decreased significantly during the NE infusion. During the NE infusion after PHE, average HR and mean blood pressure returned to baseline levels. However, MSNA (4 ± 2 bursts/min), LF power of HR (33 ± 9 normalized units), and systolic blood pressure variability (1.7 ± 1.1 mmHg2) remained significantly ( P < 0.05 for all) below baseline values. Baroreflex gain did not change significantly during the interventions. Elevated levels of circulating NE cause a feedback inhibition on sympathetic outflow in healthy subjects. These inhibitory effects do not seem to be mediated by pressor effects on the baroreflex loop but perhaps by a presynaptic autoregulatory feedback mechanism or some other mechanism that is not prevented by a nonselective α-adrenergic blockade.
Frequency-dependent and proarrhythmogenic effects of FK-506 in rat ventricular cells
Authors: Fauconnier Jérémy , Lacampagne Alain , Rauzier Jean-Michel , Fontanaud Pierre , Frapier Jean-Marc , Sejersted Ole M. , Vassort Guy , Richard Sylvain
Published: October 2004

FK-506, a widely used immunosuppressant, has caused a few clinical cases with QT prolongation and torsades de pointe at high blood concentration. The proarrhytmogenic potential of FK-506 was investigated in single rat ventricular cells using the whole cell clamp method to record action potentials (APs) and ionic currents. Fluorescence measurements of Ca2+ transients were performed with indo-1 AM using a multiphotonic microscope. FK-506 (25 μmol/l) hyperpolarized the resting membrane potential (RMP; −3 mV) and prolonged APs (AP duration at 90% repolarization increased by 21%) at 0.1 Hz. Prolongation was enhanced by threefold at 3.3 Hz, and early afterdepolarizations (EADs) occurred in 59% of cells. EADs were prevented by stronger intracellular Ca2+ buffering (EGTA: 10 vs. 0.5 mmol/l in the patch pipette) or replacement of extracellular Na+ by Li+, which abolishes Na+/Ca2+ exchange [Na+/Ca2+ exchanger current ( INaCa)]. In indo-1-loaded cells, FK-506 generated doublets of Ca2+ transients associated with increased diastolic Ca2+ in one-half of the cells. FK-506 reversibly decreased the L-type Ca2+ current ( ICaL) by 25%, although high-frequency-dependent facilitation of ICaL persisted, and decreased three distinct K+ currents: delayed rectifier K+ current ( IK; >80%), transient outward K+ current (<20%), and inward rectifier K+ current ( IK1; >40%). A shift in the reversal potential of IK1 (−5 mV) accounted for RMP hyperpolarization. Numerical simulations, reproducing all experimental effects of FK-506, and the use of nifedipine showed that frequency-dependent facilitation of ICaL plays a role in the occurrence of EADs. In conclusion, the effects of FK-506 on the cardiac AP are more complex than previously reported and include inhibitions of IK1 and ICaL. Alterations in Ca2+ release and INaCa may contribute to FK-506-induced AP prolongation and EADs in addition to the permissive role of ICaL facilitation at high rates of stimulation.
Characteristics of the aortic elastic network and related phenotypes in seven inbred rat strains
Authors: Behmoaras Jacques , Osborne-Pellegrin Mary , Gauguier Dominique , Jacob Marie-Paule
Published: October 2004

Extracellular matrix (ECM) molecules such as elastin and collagen provide mechanical support to the vessel wall and are essential for vascular function. Evidence that genetic factors influence aortic ECM composition and organization was concluded from our previous studies showing that the inbred Brown Norway (BN) rat differs significantly from the outbred Long-Evans (LE) and the inbred LOU rat with respect to both thoracic aortic elastin content and internal elastic lamina (IEL) rupture in the abdominal aorta and iliac arteries. Here, we measured aortic elastin and collagen contents as well as factors that may modulate these parameters [insulin growth factor (IGF)-I, transforming growth factor (TGF)-β1, and matrix metalloproteinase (MMP)-2] in seven inbred rat strains, including BN and LOU. We also investigated whether IEL ruptures occur in strains other than BN. We showed that LOU, LE, BN, and Fischer 344 (F344) rats were significantly different for aortic elastin content and elastin-to-collagen ratio, whereas LE, Lewis, WAG, and Wistar-Furth (WF) were similar for these parameters. BN and F344 had the lowest values. BN was the only strain to present numerous IEL ruptures, whereas F344, LE, and WF presented a few and the other strains presented none. In addition, IGF-I and TGF-β1levels in the plasma and aorta differed significantly between strains, suggesting genetic control of their production. Because inbred rat strains provide interesting models for quantitative trait locus analysis, our results concerning elastin, collagen, IEL ruptures, and cytokines may provide a basis for the search for candidate genes involved in the control of these phenotypes.
Reciprocal splanchnic-thoracic blood volume changes during the Valsalva maneuver
Authors: Stewart Julian M. , Montgomery Leslie D.
Published: October 2004

The Valsalva maneuver is frequently used to test autonomic function. Previous work demonstrated that the blood pressure decrease during the Valsalva maneuver relates to thoracic hypovolemia, which may preclude pressure recovery during phase II, even with normal resting peripheral vasoconstriction. We hypothesized that increased regional blood volume, specifically splanchnic hypervolemia, accounts for the degree of thoracic hypovolemia during the Valsalva maneuver. We studied 17 healthy volunteers aged 15–22 yr. All had normal blood volumes by dye dilution. Subjects also had normal vascular resistance while supine as well as normal vasoconstrictor responses during 35° upright tilt. We assessed changes in estimated splanchnic, pelvic-thigh, and lower leg blood volume, along with thoracic blood volume shifts, by impedance plethysmography before and during the Valsalva maneuver performed in the supine position. Early increases in splanchnic blood volume dominated the regional vascular changes during the Valsalva maneuver. The increase in splanchnic blood volume correlated well ( r2= 0.65, P < 0.00001) with the decrease in thoracic blood volume, there was less correlation of the increase in pelvic blood volume ( r2= 0.21, P < 0.03), and there was no correlation of the increase in leg blood volume ( r2= 0.001, P = 0.9). There was no relation of thoracic hypovolemia with blood volume or peripheral resistance in supine or upright positions. Thoracic hypovolemia during the Valsalva maneuver is closely related to splanchnic hyperemia and weakly related to regional changes in blood volume elsewhere. Changes in baseline splanchnic vascular properties may account for variability in thoracic blood volume changes during the Valsalva maneuver.
VEGF receptor antagonism blocks arteriogenesis, but only partially inhibits angiogenesis, in skeletal muscle of exercise-trained rats
Authors: Lloyd Pamela G. , Prior Barry M. , Li Han , Yang Hsiao T. , Terjung Ronald L.
Published: October 2004

Both collateral vessel enlargement (arteriogenesis) and capillary growth (angiogenesis) in skeletal muscle occur in response to exercise training. Vascular endothelial growth factor (VEGF) is implicated in both processes. Thus we examined the effect of a VEGF receptor (VEGF-R) inhibitor (ZD4190, AstraZeneca) on collateral-dependent blood flow in vivo and collateral artery size ex vivo (indicators of arteriogenesis) and capillary contacts per fiber (CCF; an index of angiogenesis) in skeletal muscle of both sedentary and exercise-trained rats 14 days after bilateral occlusion of the femoral arteries. Total daily treadmill run time increased appreciably from ∼70 to ∼100 min (at 15–20 m/min, twice per day) and produced a large (∼75%, P < 0.01) increase in calf muscle blood flow and a greater size of the collateral artery (wall cross-sectional area). ZD4190, which previously has been shown to inhibit the activity of VEGF-R2 and -R1 tyrosine kinase in vitro (IC50 = 30 and 700 nM, respectively), completely blocked the increase in collateral-dependent blood flow and inhibited collateral vessel enlargement. Thus exercise-stimulated collateral arteriogenesis appears to be completely dependent on VEGF-R signaling. Interestingly, enhanced mRNA expression of the VEGF family ligand placental growth factor (2- to 3.5-fold), VEGF-R1 (∼2-fold), and endothelial nitric oxide synthase (2- to 3.5-fold) in an isolated collateral artery implicates these factors as important in arteriogenesis. Training of ischemic muscle also induced angiogenesis, as shown by an increase (∼25%, P < 0.01) in CCF in white gastrocnemius muscle. VEGF-R inhibition only partially blocked ( P < 0.01) but did not eliminate the increase ( P < 0.01) in capillarity. Our findings indicate that VEGF-R tyrosine kinase activity is essential for collateral arteriogenesis and important for the angiogenesis induced in ischemic muscle by exercise training; however, other angiogenic stimuli are also important for angiogenesis in flow-limited active muscle.
Embryonic stem cells form an organized, functional cardiac conduction system in vitro
Authors: White Steven M. , Claycomb William C.
Published: October 2004

A functional pacemaking-conduction system is essential for maintaining normal cardiac function. However, no reproducible model system exists for studying the specialized cardiac pacemaking-conduction system in vitro. Although several molecular markers have been shown to delineate components of the cardiac conduction system in vivo, the functional characteristics of the cells expressing these markers remain unknown. The ability to accurately identify cells that function as cardiac pacemaking cells is crucial for being able to study their molecular phenotype. In differentiating murine embryonic stem cells, we demonstrate the development of an organized cardiac pacemaking-conduction system in vitro using the coexpression of the minK-lacZ transgene and the chicken GATA6 (cGATA6) enhancer. These markers identify clusters of pacemaking “nodes” that are functionally coupled with adjacent contracting regions. cGATA6-positive cell clusters spontaneously depolarize, emitting calcium signals to surrounding contracting regions. Physically separating cGATA6-positive cells from nearby contracting regions reduces the rate of spontaneous contraction or abolishes them altogether. cGATA6/ minK copositive cells isolated from embryoid cells display characteristics of specialized pacemaking-conducting cardiac myocytes with regard to morphology, action potential waveform, and expression of a hyperpolarization-activated depolarizing current. Using the cGATA6 enhancer, we have isolated cells that exhibit electrophysiological and genetic properties of cardiac pacemaking myocytes. Using molecular markers, we have generated a novel model system that can be used to study the functional properties of an organized pacemaking-conducting contracting system in vitro. Moreover, we have used a molecular marker to isolate a renewable population of cells that exhibit characteristics of cardiac pacemaking myocytes.
Daily exercise-induced cardioprotection is associated with changes in calcium regulatory proteins in hypertensive rats
Authors: Collins Heidi L. , Loka Alfred M. , DiCarlo Stephen E.
Published: October 2004

Epidemiological data document that regular exercise protects against the morbidity and mortality associated with ischemic heart disease. Therefore, we tested the hypothesis that daily exercise (DE) increases the ventricular arrhythmia threshold (VAT) induced by coronary artery occlusion and alters the expression of calcium regulatory proteins. The VAT was defined as the time from coronary occlusion to sustained ventricular tachycardia resulting in a reduction in arterial pressure. To test this hypothesis, we recorded the VAT in conscious sedentary normotensive, sedentary hypertensive, and DE hypertensive rats, and we associated these thresholds with the protein expression of the L-type calcium channel, Na+/Ca2+exchanger, phospholamban, and sarco(endo)plasmic reticulum Ca2+-ATPase. Results document a significantly reduced time to ventricular arrhythmias (sedentary hypertensive, 3.7 ± 0.3 min vs. sedentary normotensive, 4.8 ± 0.3 min), an increased Na+/Ca2+exchanger protein expression (47%), and a decreased phospholamban protein expression (−34%) in conscious hypertensive rats. DE increased the VAT (5.9 ± 0.2 min), decreased the protein expression of the Na+/Ca2+exchanger, and normalized the protein expression of phospholamban in the hypertensive rats. Thus DE may be a primary prevention approach for reducing the incidence of arrhythmias by altering calcium regulatory proteins in hypertensive rats.
Induced angiogenesis with intramedullary direct current: experimental research
Authors: Inan Muharrem , Alat Ilker , Gurses Iclal , Kekilli Ersoy , Kutlu Ramazan , Eskin Ahmet , Aydin Omer Murat , Bostan Haci , Yologlu Saim
Published: October 2004

The purpose of this study was to evaluate angiogenesis after the use of intramedullary direct electrical current in rabbit tibia. Thirty-two New Zealand rabbits were divided into four groups: group 1, false electrode group; group 2, hole group; group 3, control group; and group 4, intramedullary electrical stimulation group. One-half of the rabbits in each group were evaluated angiographically, pathologically, and scintigraphically on day 7, and the rest were evaluated on day 21. Results proved that electrical stimulation was not capable of the induction of angiogenesis in the subjects killed on day 7 and day 21. Furthermore, we found some fibrotic changes secondary to electrical stimulation on day 7 ( P = 0.04) and day 21 ( P = 0.01). However, an increase in new capillary vessels occurred in the false electrode group ( P = 0.02). We found no useful effect of electrical stimulation in our study, a finding that is possibly due to our use of a method previously undocumented in the literature. We believe that this study can be the new baseline for further studies into the stimulation or inhibition of angiogenesis using intramedullary wire with or without electrical stimulation.
Mechanisms of serum potentiation of GM-CSF production by human airway smooth muscle cells
Authors: Lalor D. J. , Truong B. , Henness S. , Blake A. E. , Ge Q. , Ammit A. J. , Armour C. L. , Hughes J. M.
Published: October 2004

Inflammation and vascular leakage are prevalent in asthma. This study aimed to elucidate the mechanisms involved in serum potentiation of cytokine-induced granulocyte macrophage colony stimulating factor (GM-CSF) production by human airway smooth muscle cells and to identify possible factors responsible. Serum-deprived cells at low density were stimulated with TNF-α and IL-1β for 24 h. Human AB serum (10%), inhibitors of RNA and protein synthesis or specific signaling molecules, or known smooth muscle mitogens were then added for 24 h. Culture supernatants were analyzed for GM-CSF levels, and cells were harvested to assess viability, cell cycle progression, GM-CSF-specific mRNA content, and p38 phosphorylation. Serum potentiated GM-CSF release when added before, together with (maximal), or after the cytokines. The potentiation involved both new GM-CSF-specific mRNA production and protein synthesis. The mitogens IGF, PDGF, and thrombin all potentiated GM-CSF release, and neutralizing antibodies for EGF, IGF, and PDGF reduced the serum potentiation. Inhibitor studies ruled as unlikely the involvement of p70S6kinase and the MAPK p42/p44, two signaling pathways implicated in proliferation, and the involvement of the MAPK JNK, while establishing roles for p38 MAPK and NF-κB in the potentiation of GM-CSF release. Detection of significant p38 phosphorylation in response to serum stimulation, through Western blotting, further demonstrated the involvement of p38. These studies have provided evidence to support p38 being targeted to interrupt the cycle of inflammation, vascular leakage and cytokine production in asthma.
Rhythms of ghrelin, leptin, and sleep in rats: effects of the normal diurnal cycle, restricted feeding, and sleep deprivation
Authors: Bodosi B. , Gardi J. , Hajdu I. , Szentirmai E. , Obal F. , Krueger J. M.
Published: October 2004

To determine the relationships among plasma ghrelin and leptin concentrations and hypothalamic ghrelin contents, and sleep, cortical brain temperature (Tcrt), and feeding, we determined these parameters in rats in three experimental conditions: in free-feeding rats with normal diurnal rhythms, in rats with feeding restricted to the 12-h light period (RF), and in rats subjected to 5-h of sleep deprivation (SD) at the beginning of the light cycle. Plasma ghrelin and leptin displayed diurnal rhythms with the ghrelin peak preceding and the leptin peak following the major daily feeding peak in hour 1 after dark onset. RF reversed the diurnal rhythm of these hormones and the rhythm of rapid-eye-movement sleep (REMS) and significantly altered the rhythm of Tcrt. In contrast, the duration and intensity of non-REMS (NREMS) were hardly responsive to RF. SD failed to change leptin concentrations, but it promptly stimulated plasma ghrelin and induced eating. SD elicited biphasic variations in the hypothalamic ghrelin contents. SD increased plasma corticosterone, but corticosterone did not seem to influence either leptin or ghrelin. The results suggest a strong relationship between feeding and the diurnal rhythm of leptin and that feeding also fundamentally modulates the diurnal rhythm of ghrelin. The variations in hypothalamic ghrelin contents might be associated with sleep-wake activity in rats, but, unlike the previous observations in humans, obvious links could not be detected between sleep and the diurnal rhythms of plasma concentrations of either ghrelin or leptin in the rat.
Plantar vibration improves leg fluid flow in perimenopausal women
Authors: Stewart Julian M. , Karman Carol , Montgomery Leslie D. , McLeod Kenneth J.
Published: October 2004

Recent studies have indicated that plantar-based vibration may be an effective approach for the prevention and treatment of osteoporosis. We addressed the hypothesis of whether the plantar vibration operated by way of the skeletal muscle pump, resulting in enhanced blood and fluid flow to the lower body. We combined plantar stimulation with upright tilt table testing in 18 women aged 46–63 yr. We used strain-gauge plethysmography to measure calf blood flow, venous capacitance, and the microvascular filtration relation, as well as impedance plethysmography to examine changes in leg, splanchnic, and thoracic blood flow while supine at a 35° upright tilt. A vibrating platform was placed on the footboard of a tilt table, and measurements were made at 0, 15, and 45 Hz with an amplitude of 0.2 g point to point, presented in random order. Impedance-measured supine blood flows were significantly ( P = 0.05) increased in the calf (30%), pelvic (26%), and thoracic regions (20%) by plantar vibration at 45 Hz. Moreover, the 25–35% decreases in calf and pelvic blood flows associated with upright tilt were reversed by plantar vibration, and the decrease in thoracic blood flow was significantly attenuated. Strain-gauge measurements showed an attenuation of upright calf blood flow. In addition, the microvascular filtration relation was shifted with vibration, producing a pronounced increase in the threshold for edema, Pi, due to enhanced lymphatic flow. Supine values for Pi increased from 24 ± 2 mmHg at 0 Hz to 27 ± 3 mmHg at 15 Hz, and finally to 31 ± 2 mmHg at 45 Hz ( P < 0.01). Upright values for Pi increased from 25 ± 3 mmHg at 0 Hz, to 28 ± 4 mmHg at 15 Hz, and finally to 35 ± 4 mmHg at 45 Hz. The results suggest that plantar vibration serves to significantly enhance peripheral and systemic blood flow, peripheral lymphatic flow, and venous drainage, which may account for the apparent ability of such stimuli to influence bone mass.
Role of paraventricular nucleus in the cardiogenic sympathetic reflex in rats
Authors: Zahner Matthew R. , Pan Hui-Lin
Published: October 2004

Myocardial ischemia stimulates cardiac spinal afferents to initiate a sympathoexcitatory reflex. However, the pathways responsible for generation of increased sympathetic outflow in this reflex are not fully known. In this study, we determined the role of the paraventricular nucleus (PVN) in the cardiogenic sympathetic reflex. Renal sympathetic nerve activity (RSNA) and blood pressure were recorded in anesthetized rats during epicardial application of 10 μg/ml bradykinin. Bilateral microinjection of muscimol (0.5 nmol), a GABAA receptor agonist, was performed to inhibit the PVN. In 10 vehicle-injected rats, epicardial bradykinin significantly increased RSNA 178.4 ± 48.5% from baseline, and mean arterial pressure from 76.9 ± 2.0 to 102.3 ± 3.3 mmHg. Microinjection of muscimol into the PVN significantly reduced the basal blood pressure and RSNA ( n = 12). After muscimol injection, the bradykinin-induced increases in RSNA (111.6 ± 35.9% from baseline) and mean arterial pressure (61.2 ± 1.3 to 74.5 ± 2.7 mmHg) were significantly reduced compared with control responses. The response remained attenuated even when the basal blood pressure was restored to the control. In a separate group of rats ( n = 9), bilateral microinjection of the ionotropic glutamate antagonist kynurenic acid (4.82 or 48.2 nmol in 50 nl) had no significant effect on the RSNA and blood pressure responses to bradykinin compared with controls. These results suggest that the tonic PVN activity is important for the full manifestation of the cardiogenic sympathoexcitatory response. However, ionotropic glutamate receptors in the PVN are not directly involved in this reflex response.
Oxidant stress in kidneys of spontaneously hypertensive rats involves both oxidase overexpression and loss of extracellular superoxide dismutase
Authors: Adler S. , Huang H.
Published: October 2004

Oxidant stress is an important contributor to renal dysfunction and hypertension. We have previously demonstrated that regulation of renal oxygen consumption by nitric oxide (NO) is impaired in the kidney of spontaneously hypertensive rats (SHR) due to increased superoxide production. We further explored the mechanisms of enhanced oxidant stress in the kidney of SHR. Suppression of cortical oxygen consumption by bradykinin (BK) or enalaprilat (Enal), which act through stimulation of endogenous NO, was impaired in SHR (BK: −14.1 ± 1.2%; Enal: −15.5 ± 1.2%) and was restored by addition of apocynin, an inhibitor of assembly of the NAD(P)H oxidase complex (BK: −21.0 ± 0.6%; Enal: −25.3 ± 1.4%), suggesting this as the source of enhanced superoxide production. Addition of an angiotensin type 1 receptor blocker, losartan, also restored responsiveness to control levels (BK: −22.0 ± 1.1%; Enal: −23.6 ± 1.3%), suggesting that ANG II is responsible for enhanced oxidase activity. A similar defect in responsiveness to BK and Enal could be induced in Wistar-Kyoto kidneys by ANG II and was reversed by a superoxide scavenger (tempol), apocynin or losartan. Immunoblotting of cortical samples demonstrated enhanced expression of endothelial NO synthase (eNOS 1.9×) and NAD(P)H oxidase components (gp91 phox 1.6× and Rac-1 4.5×). Expression of SOD-1 and -2 were unchanged, but SOD-3 was significantly decreased in SHR (0.5×). Thus NO bioavailability is impaired in SHR owing to an ANG II-mediated increase in superoxide production in association with enhanced expression of NAD(P)H oxidase components, despite increased expression of eNOS. Loss of SOD-3, an important superoxide scavenger, may also contribute to enhanced oxidant stress.
Microvascular permeability, ultrafiltration, and restricted diffusion
Authors: Michel C. C.
Published: October 2004

This essay looks at the historical significance of two APS classic papers that are freely available online:

Pappenheimer JR and Soto-Rivera A. Effective osmotic pressure of the plasma proteins and other quantities associated with the capillary circulation in the hindlimbs of cats and dogs. Am J Physiol 152: 471–491, 1948 ( http://ajplegacy.physiology.org/cgi/reprint/152/3/471 ).

Pappenheimer JR, Renkin EM, and Borrero LM. Filtration, diffusion and molecular sieving through peripheral capillary membranes: a contribution to the pore theory of capillary permeability. Am J Physiol 167: 13–46, 1951 ( http://ajplegacy.physiology.org/cgi/reprint/167/1/13 ).
The significance of the blood gas analyzer
Authors: Raff Hershel
Published: October 2004

This essay looks at the historical significance of an APS classic paper that is freely available online:

Severinghaus JW and Bradley AF. Electrodes for blood Po2 and Pco2 determination. J Appl Physiol 13: 515—520, 1958 ( http://jap.physiology.org/cgi/reprint/13/3/515 ).
Discovering the role of the adrenal gland in the control of body function
Authors: Randall David C.
Published: October 2004

This essay looks at the historical significance of three APS classic papers that are freely available online:

Cannon WB and de la Paz D. Emotional stimulation of adrenal secretion. Am J Physiol 28: 64-70, 1911 ( http://ajplegacy.physiology.org/cgi/reprint/28/1/64 ).

Cannon WB. The emergency function of the adrenal medulla in pain and the major emotions. Am J Physiol 33: 356-372, 1914 ( http://ajplegacy.physiology.org/cgi/reprint/33/2/356 ).

Cannon WB. Studies on the conditions of activity in endocrine glands. V. The isolated heart as an indicator of adrenal secretion induced by pain, asphyxia and excitement. Am J Physiol 50: 399-432, 1919 ( http://ajplegacy.physiology.org/cgi/reprint/50/3/399 ).
Micropuncture: unlocking the secrets of renal function
Authors: Sands Jeff M.
Published: October 2004

This essay looks at the historical significance of five APS classic papers that are freely available online:

Wearn JT and Richards AN. Observations on the composition of glomerular urine, with particular reference to the problem of reabsorption in the renal tubules. Am J Physiol 71: 209—227, 1924 ( http://ajplegacy.physiology.org/cgi/reprint/71/1/209 ).

Richards AN and Walker AM. Methods of collecting fluid from known regions of the renal tubules of Amphibia and of perfusing the lumen of a single tubule. Am J Physiol 118: 111—120, 1936 ( http://ajplegacy.physiology.org/cgi/reprint/118/1/111 ).

Walker AM and Hudson CL. The reabsorption of glucose from the renal tubule in Amphibia and the action of phlorhizin upon it. Am J Physiol 118: 130—143, 1936 ( http://ajplegacy.physiology.org/cgi/reprint/118/1/130 ).

Walker AM and Oliver J. Methods for the collection of fluid from single glomeruli and tubules of the mammalian kidney. Am J Physiol 134: 562—579, 1941 ( http://ajplegacy.physiology.org/cgi/reprint/134/3/562 ).

Walker AM, Bott PA, Oliver J, and MacDowell MC. The collection and analysis of fluid from single nephrons of the mammalian kidney. Am J Physiol 134: 580—595, 1941 ( http://ajplegacy.physiology.org/cgi/reprint/134/3/580 ).
Anterior pituitary hormones: development of a bioassay leading to the discovery of prolactin
Authors: Smith M. Susan
Published: October 2004

This essay looks at the historical significance of an APS classic paper that is freely available online:

Riddle O, Bates RW, and Dykshorn SW. The preparation, identification and assay of prolactin–a hormone of the anterior pituitary. Am J Physiol 105: 191—216, 1933 ( http://ajplegacy.physiology.org/cgi/reprint/105/1/191 ).
Postural changes in lung volumes and respiratory resistance in subjects with obesity
Authors: Watson R. A. , Pride N. B.
Published: October 2004

Reduced functional residual capacity (FRC) is consistently found in obese subjects. In 10 obese subjects (mean ± SE age 49.0 ± 6 yr, weight 128.4 ± 8 kg, body mass index 44 ± 3 kg/m2) without respiratory disease, we examined 1) supine changes in total lung capacity (TLC) and subdivisions, 2) whether values of total respiratory resistance (Rrs) are appropriate for mid-tidal lung volume (MTLV), and 3) estimated resistance of the nasopharyngeal airway (Rnp) in both sitting and supine postures. The results were compared with those of 13 control subjects with body mass indexes of <27kg/m2. Rrs at 6 Hz was measured by applying forced oscillation at the mouth (Rrs,mo) or the nose (Rrs,na); Rnp was estimated from the difference between sequential measurements of Rrs,mo and Rrs,na. All measurements were made when subjects were seated and when supine. Obese subjects when seated had a restrictive defect with low TLC and FRC-to-TLC ratio; when supine, TLC fell 80 ml and FRC fell only 70 ml compared with a mean supine fall of FRC of 730 ml in control subjects. Values of Rrs,mo and Rrs,na at resting MTLV in obese subjects were about twice those in control subjects in both postures. Relating total respiratory conductance (1/Rrs) to MTLV, the increase in Rrs,mo in obese subjects was only partly explained by their reduced MTLV. Rnp was increased in some obese subjects in both postures. Despite the increased extrapulmonary mass load in obese subjects, further falls in TLC and FRC when supine were negligible. Rrs,mo at isovolume was increased. Further studies are needed to examine the causes of reduced TLC and increases in Rrs,mo and sometimes in Rnp in obese subjects.