bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of ADP-ribose in 11,12-EET-induced activation of KCachannels in coronary arterial smooth muscle cells
Authors: Li Pin-Lan , Zhang David X. , Ge Zhi-Dong , Campbell William B.
Published: March 2015

We recently reported that cADP-ribose (cADPR) and ADP-ribose (ADPR) play an important role in the regulation of the Ca2+-activated K+(KCa) channel activity in coronary arterial smooth muscle cells (CASMCs). The present study determined whether these novel signaling nucleotides participate in 11,12-epoxyeicosatrienoic acid (11,12-EET)-induced activation of the KCachannels in CASMCs. HPLC analysis has shown that 11,12-EET increased the production of ADPR but not the formation of cADPR. The increase in ADPR production was due to activation of NAD glycohydrolase as measured by a conversion rate of NAD into ADPR. The maximal conversion rate of NAD into ADPR in coronary homogenate was increased from 2.5 ± 0.2 to 3.4 ± 0.3 nmol · min−1· mg protein−1by 11,12-EET. The regioisomers of 8,9-EET, 11,12-EET, and 14,15-EET also significantly increased ADPR production from NAD. Western blot analysis and immunoprecipitation demonstrated the presence of NAD glycohydrolase, which mediated 11,12-EET-activated production of ADPR. In cell-attached patches, 11,12-EET (100 nM) increases KCachannel activity by 5.6-fold. The NAD glycohydrolase inhibitor cibacron blue 3GA (3GA, 100 μM) significantly attenuated 11,12-EET-induced increase in the KCachannel activity in CASMCs. However, 3GA had no effect on the KCachannels activity in inside-out patches. 11,12-EET produced a concentration-dependent relaxation of precontracted coronary arteries. This 11,12-EET-induced vasodilation was substantially attenuated by 3GA (30 μM) with maximal inhibition of 57%. These results indicate that 11,12-EET stimulates the production of ADPR and that intracellular ADPR is an important signaling molecule mediating 11,12-EET-induced activation of the KCachannels in CASMCs and consequently results in vasodilation of coronary artery.
High-cut characteristics of the baroreflex neural arc preserve baroreflex gain against pulsatile pressure
Authors: Kawada Toru , Zheng Can , Yanagiya Yusuke , Uemura Kazunori , Miyamoto Tadayoshi , Inagaki Masashi , Shishido Toshiaki , Sugimachi Masaru , Sunagawa Kenji
Published: March 2015

A transfer function from baroreceptor pressure input to sympathetic nerve activity (SNA) shows derivative characteristics in the frequency range below 0.8 Hz in rabbits. These derivative characteristics contribute to a quick and stable arterial pressure (AP) regulation. However, if the derivative characteristics hold up to heart rate frequency, the pulsatile pressure input will yield a markedly augmented SNA signal. Such a signal would saturate the baroreflex signal transduction, thereby disabling the baroreflex regulation of AP. We hypothesized that the transfer gain at heart rate frequency would be much smaller than that predicted from extrapolating the derivative characteristics. In anesthetized rabbits ( n = 6), we estimated the neural arc transfer function in the frequency range up to 10 Hz. The transfer gain was lost at a rate of −20 dB/decade when the input frequency exceeded 0.8 Hz. A numerical simulation indicated that the high-cut characteristics above 0.8 Hz were effective to attenuate the pulsatile signal and preserve the open-loop gain when the baroreflex dynamic range was finite.
Flow through internal elastic lamina affects shear stress on smooth muscle cells (3D simulations)
Authors: Tada Shigeru , Tarbell John M.
Published: March 2015

We describe a three-dimensional numerical simulation of interstitial flow through the medial layer of an artery accounting for the complex entrance condition associated with fenestral pores in the internal elastic lamina (IEL) to investigate the fluid mechanical environment around the smooth muscle cells (SMCs) right beneath the IEL. The IEL was modeled as an impermeable barrier to water flow except for the fenestral pores, which were assumed to be uniformly distributed over the IEL. The medial layer was modeled as a heterogeneous medium composed of a periodic array of cylindrical SMCs embedded in a continuous porous medium representing the interstitial proteoglycan and collagen matrix. Depending on the distance between the IEL bottom surface and the upstream end of the proximal layer of SMCs, the local shear stress on SMCs right beneath the fenestral pore could be more than 10 times higher than that on the cells far removed from the IEL under the conditions that the fenestral pore diameter and area fraction of pores were kept constant at 1.4 μm and 0.05, respectively. Thus these proximal SMCs may experience shear stress levels that are even higher than endothelial cells exposed to normal blood flow (order of 10 dyn/cm2). Furthermore, entrance flow through fenestral pores alters considerably the interstitial flow field in the medial layer over a spatial length scale of the order of the fenestral pore diameter. Thus the spatial gradient of shear stress on the most superficial SMC is noticeably higher than computed for endothelial cell surfaces.
Flow and pressure distributions in vascular networks consisting of distensible vessels
Authors: Krenz Gary S. , Dawson Christopher A.
Published: March 2015

We examine the influence of vessel distensibility on the fraction of the total network flow passing through each vessel of a model vascular network. An exact computational methodology is developed yielding an analytic proof. For a class of structurally heterogeneous asymmetric vascular networks, if all the individual vessels share a common distensibility relation when the total network flow is changed, this methodology proves that each vessel will continue to receive the same fraction of the total network flow. This constant flow partitioning occurs despite a redistribution of pressures, which may result in a decrease in the diameter of one and an increase in the diameter of the other of two vessels having a common diameter at a common pressure. This theoretical observation, taken along with published experimental observations on pulmonary vessel distensibilities, suggests that vessel diameter-independent distensibility in the pulmonary vasculature may be an evolutionary adaptation for preserving the spatial distribution of pulmonary blood flow in the face of large variations in cardiac output.
Impaired collateral development in mature rats
Authors: Tuttle Jay L. , Hahn Tara L. , Sanders Bridget M. , Witzmann Frank A. , Miller Steven J. , Dalsing Michael C. , Unthank Joseph L.
Published: March 2015

The effect of maturation on collateral development of resistance arteries was investigated. Three to four sequential mesenteric arteries were ligated to create collateral pathways in anesthetized young (∼200 g) and mature (∼600 g) rats. Blood flow was similarly elevated in collaterals of young and mature animals. In vivo inner arterial diameter was increased only within young collaterals (33 ± 7%, P < 0.001). Increases in number of intimal nuclei (57 ± 10% vs. 52 ± 14%) and cross-sectional medial area (33 ± 13% vs. 38 ± 5%) were similar between young and mature collaterals. Relative to the same animal controls, collateral endothelial nitric oxide synthase mRNA was increased as much in mature as in young rats. Proteomic analysis revealed significant differences in protein expression with maturation between control arteries as well as flow-loaded collateral vessels. The results indicate that, whereas intimal and medial remodeling events were similar in collaterals of young and mature rats, luminal expansion occurred only in young rats. Alteration in arterial protein expression with maturation and altered responses to stimuli for collateral development may contribute to this impairment.
Protein kinase C-δ modulates apoptosis induced by hyperglycemia in adult ventricular myocytes
Authors: Shizukuda Yukitaka , Reyland Mary E. , Buttrick Peter M.
Published: March 2015

We evaluated the direct effect of hyperglycemia on apoptosis of adult rat ventricular myocytes (ARVM) in vitro. Hyperglycemia (16.5 mM) for 24 h increased apoptosis by greater than threefold (48.2 ± 4.4%, by the TdT-mediated dUTP nick-end labeling method) compared with baseline (14.7 ± 2.5%). Hyperosmolarity with mannitol (11.0 mM) in the presence of 5.5 mM glucose also increased apoptosis by approximately twofold of baseline. Both glucose and mannitol treatment resulted in the membrane translocation of protein kinase C (PKC)-δ, and the activation of PKC-δ was confirmed by immune complex kinase assay. PKC-δ-specific translocation inhibitor peptide (δV1-1) attenuated only apoptosis induced by hyperglycemia but not by mannitol. A PKC-ɛ-specific translocation inhibitor peptide (ɛV1-1) affected neither type of apoptosis. Moderate overexpression of PKC-δ by adenovirus gene transfer prevented the antiapoptotic effect of δV1-1. Furthermore, δV1-1 attenuated the production of reactive oxygen species (ROS) by glucose. Taken together, our results indicate that increased ROS production regulated by PKC-δ is in part responsible for the induction of apoptosis by hyperglycemia and that apoptosis by hyperglycemia is mechanistically different from that by hyperosmolarity.
Modulation of mitochondrial nitric oxide synthase and energy expenditure in rats during cold acclimation
Authors: Peralta Jorge Guillermo , Finocchietto Paola V. , Converso Daniela , Schöpfer Francisco , Carreras Marı́a Cecilia , Poderoso Juan José
Published: March 2015

To preserve thermoneutrality, cold exposure is followed by changes in energy expenditure and basal metabolic rate (BMR). Because nitric oxide (NO) modulates mitochondrial O2 uptake and energy levels, we analyzed cold effects (30 days at 4°C) on rat liver and skeletal muscle mitochondrial NO synthases (mtNOS) and their putative impact on BMR. Cold exposure delimited two periods: A ( days 1–10), with high systemic O2 uptake and weight loss, and B ( days 10–30), with lower O2 uptake and fat deposition. mtNOS activity and expression decreased in period A and then increased in period B by 60–100% in liver and skeletal muscle ( P< 0.05). Conversely, mitochondrial O2 uptake remained initially high in the presence of l-arginine and later fell by 30–50% ( P < 0.05). On this basis, the estimated fractional contribution of liver plus muscle to total BMR varied from 40% in period A to 25% in period B. The transitional modulation of mtNOS in rat cold acclimation could participate in adaptive responses that favor calorigenesis or conservative energy-saving mechanisms.
Activation of cardiac ryanodine receptors by the calcium channel agonist FPL-64176
Authors: Wasserstrom J. Andrew , Wasserstrom Leslie A. , Lokuta Andrew J. , Kelly James E. , Reddy Sireen T. , Frank Andrew J.
Published: March 2015

We investigated the possibility that the Ca2+ channel agonist FPL-64176 (FPL) might also activate the cardiac sarcoplasmic reticulum (SR) Ca2+ release channel ryanodine receptor (RyR). The effects of FPL were tested on single channel activity of purified and crude vesicular RyR (RyR2) isolated from human and dog hearts using the planar lipid bilayer technique. FPL (100–200 μM) increased single channel open probability ( P o) when added to the cytoplasmic side of the channel ( P o = 0.070 ± 0.021 in control RyR2; 0.378 ± 0.086 in 150 μM FPL, n = 9, P < 0.01) by prolonging open times and decreasing closed times without changing current magnitude. FPL had no effect on P o when added to the trans (luminal) side of the bilayer ( P o = 0.079 ± 0.036 in control and 0.103 ± 0.066 in FPL, n = 4, no significant difference). The bell-shaped [Ca2+] dependence of [3H]ryanodine binding and of P o was altered by FPL, suggesting that the mechanism by which FPL increases channel activity is by an increase in Ca2+-induced activation at low [Ca2+] (without a change in threshold) and suppression of Ca2+-induced inactivation at high [Ca2+]. However, the fact that inactivation was restored at elevated [Ca2+] suggests a competitive interaction between Ca2+ and FPL on inactivation. FPL had no effect on RyR skeletal channels (RyR1), where P o was 0.039 ± 0.005 in control versus 0.030 ± 0.006 in 150 μM FPL (no significant difference). These results suggest that, in addition to its ability to activate the L-type Ca2+channels, FPL activates cardiac RyR2 primarily by reducing the Ca2+ sensitivity of inactivation.
Vascular and metabolic response to cycle exercise in sedentary humans: effect of age
Authors: Poole J. G. , Lawrenson L. , Kim J. , Brown C. , Richardson R. S.
Published: March 2015

We measured leg blood flow (LBF), drew arterial-venous (A-V) blood samples, and calculated muscle O2 consumption (V˙o 2) during incremental cycle ergometry exercise [15, 30, and 99 W and maximal effort (maximal work rate, WRmax)] in nine sedentary young (20 ± 1 yr) and nine sedentary old (70 ± 2 yr) males. LBF was preserved in the old subjects at 15 and 30 W. However, at 99 W and at WRmax, leg vascular conductance was attenuated because of a reduced LBF (young: 4.1 ± 0.2 l/min and old: 3.1 ± 0.3 l/min) and an elevated mean arterial blood pressure (young: 112 ± 3 mmHg and old: 132 ± 3 mmHg) in the old subjects. Leg A-V O2 difference changed little with increasing WR in the old group but was elevated compared with the young subjects. Muscle maximal V˙o 2 and cycle WRmax were significantly lower in the old subjects (young: 0.8 ± 0.05 l/min and 193 ± 7 W; old: 0.5 ± 0.03 l/min and 117 ± 10 W). The submaximally unchanged and maximally reduced cardiac output associated with aging coupled with its potential maldistiribution are candidates for the limited LBF during moderate to heavy exercise in older sedentary subjects.
Cardiac interstitial bradykinin and mast cells modulate pattern of LV remodeling in volume overload in rats
Authors: Wei Chih-Chang , Lucchesi Pamela A. , Tallaj Jose , Bradley Wayne E. , Powell Pamela C. , Dell'Italia Louis J.
Published: March 2015

In the current study, interstitial fluid (ISF), bradykinin (BK), and angiotensin II (ANG II) levels were measured using cardiac microdialysis in conscious, nonsedated rats at baseline and at 48 h and 5 days after each of the following: sham surgery (sham, n = 6), sham + administration of ANG-converting enzyme inhibitor ramipril (R, n = 6), creation of aortocaval fistula (ACF, n = 6), ACF + R ( n = 6), and ACF + R + BK2receptor antagonist (HOE-140) administration ( n = 6). At 5 days, both ISF ANG II and BK increased in ACF rats ( P < 0.05); however, in ACF + R rats, ISF ANG II did not differ from basal levels and ISF BK increased greater than threefold above baseline at 2 and 5 days ( P < 0.05). Five days after ACF, the left ventricular (LV) weight-to-body weight ratio increased 30% ( P < 0.05) in ACF but did not differ from sham in ACF + R and ACF + R + HOE-140 rats despite similar systemic arterial pressures across all ACF groups. However, ACF + R + HOE-140 rats had greater postmortem wall thickness-to-diameter ratio and smaller cross-sectional diameter compared with ACF + R rats. There was a significant increase in mast cell density in ACF and ACF + R rats that decreased below sham in ACF + R + HOE-140 rats. These results suggest a potentially important interaction of mast cells and BK in the cardiac interstitium that modulates the pattern of LV remodeling in the acute phase of volume overload.
Oxygen radicals trigger activation of NF-κB and AP-1 and upregulation of ICAM-1 in reperfused canine heart
Authors: Fan Haiying , Sun Baogui , Gu Qiuping , Lafond-Walker Anne , Cao Suyi , Becker Lewis C.
Published: March 2015

We investigated whether oxygen radicals generated during ischemia-reperfusion trigger postischemic inflammation in the heart. Closed-chest dogs underwent 90-min coronary artery occlusion, followed by 1- or 3-h reperfusion: 10 dogs received the cell-permeant oxygen radical scavenger N-(2-mercaptopropionyl)-glycine (MPG; 8 mg · kg−1 · h−1intracoronary) beginning 5 min before reperfusion, and 9 dogs received vehicle. Blood flow (microspheres), intercellular adhesion molecule (ICAM)-1 protein expression (immunohistochemistry), ICAM-1 gene activation (Northern blotting), nuclear DNA binding activity of nuclear factor (NF)-κb and AP-1 (electrophoretic mobility shift assays), and neutrophil (PMN) accumulation (myeloperoxidase activity) were assessed in myocardial tissue samples. ICAM-1 protein expression was high in vascular endothelium after ischemia-reperfusion but was markedly reduced by MPG. MPG treatment also markedly decreased expression of ICAM-1 mRNA and tissue PMN accumulation. Nuclear DNA binding activities of NF-κB and AP-1, increased by ischemia-reperfusion, were both markedly decreased by MPG at 1 h of reperfusion. However, by 3 h, AP-1 activity was only modestly reduced by MPG and NF-κB activity was not significantly different from ischemic-reperfused controls. These results suggest that oxygen radicals generated in vivo during reperfusion trigger early activation of NF-κb and AP-1, resulting in upregulation of the ICAM-1 gene in vascular endothelium and subsequent tissue accumulation of activated PMNs.
Cross-bridge kinetics modeled from myoplasmic [Ca2+] and LV pressure at 17°C and after 37°C and 17°C ischemia
Authors: Rhodes Samhita S. , Ropella Kristina M. , Audi Said H. , Camara Amadou K. S. , Kevin Leo G. , Pagel Paul S. , Stowe David F.
Published: March 2015

We modeled changes in contractile element kinetics derived from the cyclic relationship between myoplasmic [Ca2+], measured by indo 1 fluorescence, and left ventricular pressure (LVP). We estimated model rate constants of the Ca2+affinity for troponin C (TnC) on actin (A) filament (TnCA) and actin and myosin (M) cross-bridge (A · M) cycling in intact guinea pig hearts during baseline 37°C perfusion and evaluated changes at 1) 20 min 17°C pressure, 2) 30-min reperfusion (RP) after 30-min 37°C global ischemia during 37°C RP, and 3) 30-min RP after 240-min 17°C global ischemia during 37°C RP. At 17°C perfusion versus 37°C perfusion, the model predicted: A · M binding was less sensitive; A · M dissociation was slower; Ca2+was less likely to bind to TnCA with A · M present; and Ca2+and TnCA binding was less sensitive in the absence of A · M. Model results were consistent with a cold-induced fall in heart rate from 260 beats/min (37°C) to 33 beats/min (17°C), increased diastolic LVP, and increased phasic Ca2+. On RP after 37°C ischemia vs. 37°C perfusion, the model predicted the following: A · M binding was less sensitive; A · M dissociation was slower; and Ca2+was less likely to bind to TnCA in the absence of A · M. Model results were consistent with reduced myofilament responsiveness to [Ca2+] and diastolic contracture on 37°C RP. In contrast, after cold ischemia versus 37°C perfusion, A · M association and dissociation rates, and Ca2+and TnCA association rates, returned to preischemic values, whereas the dissociation rate of Ca2+from A · M was ninefold faster. This cardiac muscle kinetic model predicted a better-restored relationship between Ca2+and cross-bridge function on RP after an eightfold longer period of 17°C than 37°C ischemia.
Parasympathetic effects on cardiac electrophysiology during exercise and recovery
Authors: Kannankeril Prince J. , Goldberger Jeffrey J.
Published: March 2015

Depressed parasympathetic tone is associated with an increased risk of sudden cardiac death. Exercise and the postexercise recovery period, which are associated with parasympathetic withdrawal, are high risk periods for sudden death. However, parasympathetic effects on cardiac electrophysiology during exercise and recovery have not been described. Electrophysiology studies were performed using noninvasive programmed stimulation (NIPS) in nine subjects (age 59 ± 18 yr) with implanted dual-chamber devices and normal left ventricular function during multiple bicycle exercise sessions. NIPS was performed at rest, during exercise, and in the early recovery period both before and after parasympathetic blockade with atropine. Parasympathetic effect was defined as the value of the parameter of interest in the absence of atropine minus the value of the parameter in the presence of atropine. During exercise, sinus cycle length, atrioventricular (AV) block cycle length, AV interval, and ventricular effective refractory period shortened; in recovery, the values were intermediate between the rest and exercise values ( P < 0.0001 by ANOVA). Parasympathetic effects on sinus cycle length, AV block cycle length, AV interval, and ventricular effective refractory period were 247 ± 140, 58 ± 20, 76 ± 20, and 8.6 ± 7.5 ms at rest, 106 ± 20, 37 ± 14, 24 ± 13, and 2.6 ± 7.8 ms during exercise, and 209 ± 114, 50 ± 23, 35 ± 21, and 9.5 ± 11.8 ms during recovery, respectively. There was poor correlation among the parasympathetic effects noted at the sinus node, AV node, and ventricle. Further work evaluating parasympathetic effects on cardiac electrophysiology during exercise and recovery in patients with heart disease is required to elucidate its role in modulating the risk of sudden cardiac death noted at these times.
Involvement of sympathetic nerve activity in skin blood flow oscillations in humans
Authors: Söderström Torbjörn , Stefanovska Aneta , Veber Mitja , Svensson Henry
Published: March 2015

We have used the wavelet transform to evaluate the time-frequency content of laser-Doppler flowmetry (LDF) signals measured simultaneously on the surfaces of free microvascular flaps deprived of sympathetic nerve activity (SNA), and on adjacent intact skin, in humans. It was thereby possible to determine the frequency interval within which SNA manifests itself in peripheral blood flow oscillations. The frequency interval from 0.0095 to 2 Hz was examined and was divided into five subintervals: I, ∼0.01 Hz; II, ∼0.04 Hz; III, ∼0.1 Hz; IV, ∼0.3 Hz; and V, ∼1 Hz. The average value of the LDF signal in the time domain as well as the mean amplitude and total power in the interval from 0.0095 to 2 Hz and amplitude and power within each of the five subintervals were significantly lower for signals measured on the free flap ( P < 0.002). The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals: I, from 0.0095 to 0.021 Hz; and II, from 0.021 to 0.052 Hz ( P < 0.05); thus indicating that SNA is manifested in at least one of these frequency intervals. Because interval I has recently been shown to be the result of vascular endothelial activity, we conclude that we have identified SNA as influencing blood flow oscillations in normal tissues with repetition times of 20–50 s or frequencies of 0.02–0.05 Hz.
Postexercise hypotension in conscious SHR is attenuated by blockade of substance P receptors in NTS
Authors: Chen Chao-Yin , Munch Paul A. , Quail Anthony W. , Bonham Ann C.
Published: March 2015

In hypertensive subjects, a single bout of dynamic exercise results in an immediate lowering of blood pressure back toward normal. This postexercise hypotension (PEH) also occurs in the spontaneously hypertensive rat (SHR). In both humans and SHRs, PEH features a decrease in sympathetic nerve discharge, suggesting the involvement of central nervous system pathways. Given that substance P is released in the nucleus tractus solitarius (NTS) by activation of baroreceptor and skeletal muscle afferent fibers during muscle contraction, we hypothesized that substance P acting at neurokinin-1 (NK-1) receptors in the NTS might contribute to PEH. We tested the hypothesis by determining, in conscious SHRs, whether NTS microinjections of the NK-1 receptor antagonist SR-140333 before exercise attenuated PEH. The antagonist, in a dose (60 pmol) that blocked substance P- and sparedd,l-homocysteic acid-induced depressor responses, significantly attenuated the PEH by 37%, whereas it had no effect on blood pressure during exercise. Vehicle microinjection had no effect. The antagonist also had no effect on heart rate responses during both exercise and the PEH period. The data suggest that a substance P (NK-1) receptor mechanism in the NTS contributes to PEH.
Comparison of vasodilatory properties of 14,15-EET analogs: structural requirements for dilation
Authors: Falck J. R. , Krishna U. Murali , Reddy Y. Krishna , Kumar P. Srinagesh , Reddy K. Malla , Hittner Sarah B. , Deeter Christine , Sharma Kamalesh K. , Gauthier Kathryn M. , Campbell William B.
Published: March 2015

Epoxyeicosatrienoic acids (EETs) are endothelium-derived eicosanoids that activate potassium channels, hyperpolarize the membrane, and cause relaxation. We tested 19 analogs of 14,15-EET on vascular tone to determine the structural features required for activity. 14,15-EET relaxed bovine coronary arterial rings in a concentration-related manner (ED50= 10−6M). Changing the carboxyl to an alcohol eliminated dilator activity, whereas 14,15-EET-methyl ester and 14,15-EET-methylsulfonimide retained full activity. Shortening the distance between the carboxyl and epoxy groups reduced the agonist potency and activity. Removal of all three double bonds decreased potency. An analog with a Δ8 double bond had full activity and potency. However, the analogs with only a Δ5 or Δ11 double bond had reduced potency. Conversion of the epoxy oxygen to a sulfur or nitrogen resulted in loss of activity. 14( S),15( R)-EET was more potent than 14( R),15( S)-EET, and 14,15-( cis)-EET was more potent than 14,15-( trans)-EET. These studies indicate that the structural features of 14,15-EET required for relaxation of the bovine coronary artery include a carbon-1 acidic group, a Δ8 double bond, and a 14( S),15( R)-( cis)-epoxy group.
Ischemia alters the electrical activity of pacemaker cells isolated from the rabbit sinoatrial node
Authors: Gryshchenko O. , Qu J. , Nathan R. D.
Published: March 2015

The purpose of this study was to investigate the mechanisms responsible for ischemia-induced changes in spontaneous electrical activity. An ischemic-like Tyrode solution (pH 6.6) reversibly depolarized the maximum diastolic potential (MDP) and reduced the action potential (AP) overshoot (OS). We used SNARF-1, which is an indicator of intracellular pH (pHi), and perforated-patch techniques to test the hypothesis that acidosis caused these effects. Acidic but otherwise normal Tyrode solution (pH 6.8) produced similar effects. Basic Tyrode solution (pH 8.5) hyperpolarized the MDP, shortened the AP, and slowed the firing rate. In the presence of “ischemic” Tyrode solution, hyperpolarizing current restored the MDP and OS to control values. HOE-642, an inhibitor of Na/H exchange, did not alter pHi or electrical activity and did not prevent the effects of ischemic Tyrode solution or recovery after washout. Time-independent net inward current but not hyperpolarization-activated inward current was enhanced by ischemic Tyrode solution or by 30 μM BaCl2, a selective blocker of inward-rectifying K currents at this concentration. The results suggest that 1) acidosis was responsible for the ischemia-induced effects but Na/H exchange was not involved, 2) the OS was reduced because of depolarization-induced inactivation of inward currents that generate the AP upstroke, and 3) reduction of an inward-rectifying outward K current contributed to the depolarization.
High-salt diet impairs vascular relaxation mechanisms in rat middle cerebral arteries
Authors: Lombard Julian H. , Sylvester Francis A. , Phillips Shane A. , Frisbee Jefferson C.
Published: March 2015

Male Sprague-Dawley rats were maintained on a low-salt (LS) diet (0.4% NaCl) or a high-salt (HS) diet (4% NaCl) for 3 days or 4 wk. Po 2reduction to 40–45 mmHg, the stable prostacyclin analog iloprost (10 pg/ml), and stimulatory G protein activation with cholera toxin (1 ng/ml) caused vascular smooth muscle (VSM) hyperpolarization, increased cAMP production, and dilation in cerebral arteries from rats on a LS diet. Arteries from rats on a HS diet exhibited VSM depolarization and constriction in response to hypoxia and iloprost, failed to dilate or hyperpolarize in response to cholera toxin, and cAMP production did not increase in response to hypoxia, iloprost, or cholera toxin. Low-dose angiotensin II infusion (5 ng · kg−1 · min−1iv) restored normal responses to reduced Po 2and iloprost in arteries from animals on a HS diet. These observations suggest that angiotensin II suppression with a HS diet leads to impaired relaxation of cerebral arteries in response to vasodilator stimuli acting at the cell membrane.
Different α-adrenoceptors mediate migration of vascular smooth muscle cells and adventitial fibroblasts in vitro
Authors: Zhang Hua , Facemire Carie S. , Banes Albert J. , Faber James E.
Published: March 2015

Norepinephrine directly induces growth of the vascular wall, which may involve not only proliferation of smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) but also augmentation of their migration. To test this hypothesis, growth-arrested SMCs and AFBs from rat aorta were exposed to norepinephrine. Norepinephrine caused dose-dependent migration of both cell types that was dependent on chemotaxis. In contrast, platelet-derived growth factor (PDGF)-BB, used as a positive control, stimulated both chemotaxis and chemokinesis. Only α1D-adrenoceptors (AR) and α2-AR antagonists inhibited norepinephrine migration of SMCs, whereas norepinephrine migration of AFBs was only inhibited by α1A-AR and α1B-AR antagonists; β-AR blockade was without effect. Norepinephrine and PDGF-BB were additive for AFB, but not SMC, migration. Stimulation of migration was reversed at high norepinephrine concentrations (10 μM); this inhibition was mediated by α2- and β-ARs in AFBs but not in SMCs. Thus norepinephrine induces migration of SMCs and AFBs via different α-ARs. This action may participate in wall remodeling and norepinephrine potentiation of injury-induced intimal lesion growth.
QT-RR relationship in healthy subjects exhibits substantial intersubject variability and high intrasubject stability
Authors: Batchvarov Velislav N. , Ghuran Azad , Smetana Peter , Hnatkova Katerina , Harries Monica , Dilaveris Polychronis , Camm A. John , Malik Marek
Published: March 2015

Recently, it was demonstrated that the QT-RR relationship pattern varies significantly among healthy individuals. We compared the intra- and interindividual variations of the QT-RR relationship. Twenty-four-hour 12-lead digital electrocardiograms (ECGs; SEER MC, GE Marquette; 10-s ECG recorded every 30 s) were obtained at baseline and after 24 h, 1 wk, and 1 mo in 75 healthy subjects (42 women, 33 men, age 27.9 ± 9.6 vs. 26.8 ± 7.5 yr, P = not significant). QT interval was measured automatically in each ECG by six different algorithms, and the mean of the six measurements was analyzed. In each recording of each individual, QT-RR relationship was assessed by 10 different regression models including linear (QT = β + α × RR) and parabolic (QT = β × RRα) models. Standard deviations (SDs) of regression parameters α and β of consecutive recordings of each individual were compared with SD of the individual means. Intrasubject stability and interindividual variability were further tested by ANOVA. With all models, intraindividual SDs of the regression parameters were highly significantly smaller than SD of individual means ( P < 10−5–10−9). The intrasubject stability was further confirmed by ANOVA ( P < 10−19–10−30). The QT-RR relationship exhibits substantial intersubject variability as well as a high intrasubject stability. This has practical implications for a precise estimation of the heart rate-corrected QT interval in which optimized subject-specific rate correction formulas should be used.
Mitochondrial Ca2+uptake is important over low [Ca2+]irange in arterial smooth muscle
Authors: Kamishima Tomoko , Quayle John M.
Published: March 2015

Mitochondrial Ca2+uptake is usually thought to occur only when intracellular Ca2+concentration ([Ca2+]i) is high. We investigated whether mitochondrial Ca2+removal participates in shaping [Ca2+]isignals in arterial smooth muscle over a low [Ca2+]irange. [Ca2+]iwas measured using fura 2-loaded, voltage-clamped cells from rat femoral arteries. Both diazoxide and carbonyl cyanide m-chlorophenylhydrazone (CCCP) depolarized the mitochondria. Diazoxide application increased resting [Ca2+]i, suggesting that Ca2+is sequestered in mitochondria. Over a low [Ca2+]irange, diazoxide and CCCP slowed Ca2+removal rate, determined after a brief depolarization. When [Ca2+]iwas measured during sustained depolarization to −30 mV, CCCP application increased [Ca2+]i. When Ca2+transients were repeatedly evoked by caffeine applications, CCCP application elevated resting [Ca2+]i. Caffeine-induced Ca2+transients were compared before and after CCCP application using the half decay time, or time required to reduce increase in [Ca2+]iby 50% ( t½). CCCP treatment significantly increased t½. These results suggest that Ca2+removal to mitochondria in arterial smooth muscle cells may be important at a low [Ca2+]i.
Cardiovascular responses to substance P in the nucleus tractus solitarii: microinjection study in conscious rats
Authors: Abdala Ana Paula L. , Haibara Andrea S. , Colombari Eduardo
Published: March 2015

The cardiovascular effects of substance P (SP) microinjections in the nucleus tractus solitarii (NTS) were evaluated in conscious rats. We chose this model because it is an effective way to access some of the cardiovascular effects of neurotransmitters in the NTS without the inconvenience of blunting pathways with anesthetic agents or removing forebrain projections by decerebration. The cardiovascular responses to SP injections were also evaluated after chronic nodose ganglionectomy. We found that, in conscious rats, SP microinjections into the NTS induced hypertension and tachycardia. Unilateral and bilateral SP injections into the NTS caused a slow increase in blood pressure and heart rate that peaked 1.5–5 min after injection and lasted for 20–30 min. Nodose ganglionectomy increased the duration of the pressor and tachycardic effects of SP and enhanced the pressor response. These data show that SP in the NTS is involved in pressor pathways. The supersensitivity to SP seen after nodose ganglionectomy suggests that vagal afferent projections are involved in those pressor pathways activated by SP in the NTS.
Functional and morphological evidence for a ventricular conduction system in zebrafish andXenopushearts
Authors: Sedmera David , Reckova Maria , deAlmeida Angela , Sedmerova Martina , Biermann Martin , Volejnik Jiri , Sarre Alexandre , Raddatz Eric , McCarthy Robert A. , Gourdie Robert G. , Thompson Robert P.
Published: March 2015

Zebrafish and Xenopus have become popular model organisms for studying vertebrate development of many organ systems, including the heart. However, it is not clear whether the single ventricular hearts of these species possess any equivalent of the specialized ventricular conduction system found in higher vertebrates. Isolated hearts of adult zebrafish ( Danio rerio) and African toads ( Xenopus laevis) were stained with voltage-sensitive dye and optically mapped in spontaneous and paced rhythms followed by histological examination focusing on myocardial continuity between the atrium and the ventricle. Spread of the excitation wave through the atria was uniform with average activation times of 20 ± 2 and 50 ± 2 ms for zebrafish and Xenopus toads, respectively. After a delay of 47 ± 8 and 414 ± 16 ms, the ventricle became activated first in the apical region. Ectopic ventricular activation was propagated significantly more slowly (total ventricular activation times: 24 ± 3 vs. 14 ± 2 ms in zebrafish and 74 ± 14 vs. 35 ± 9 ms in Xenopus). Although we did not observe any histologically defined tracts of specialized conduction cells within the ventricle, there were trabecular bands with prominent polysialic acid-neural cell adhesion molecule staining forming direct myocardial continuity between the atrioventricular canal and the apex of the ventricle; i.e., the site of the epicardial breakthrough. We thus conclude that these hearts are able to achieve the apex-to-base ventricular activation pattern observed in higher vertebrates in the apparent absence of differentiated conduction fascicles, suggesting that the ventricular trabeculae serve as a functional equivalent of the His-Purkinje system.
β1-Receptors increase cAMP and induce abnormal Cai cycling in the German shepherd sudden death model
Authors: Steinberg Susan F. , Alcott Sasha , Pak Elena , Hu Donglei , Protas Lev , Möise N. Sydney , Robinson Richard B. , Rosen Michael R.
Published: March 2015

We studied the role of β-adrenergic receptor subtype signaling to cAMP and calcium in the genesis of catecholamine-dependent arrhythmias in German shepherd dogs that develop lethal arrhythmias at ∼5 mo of age. There were three major findings in this study: 1) isoproterenol induces similar increases in cAMP in afflicted and control dogs exclusively through β1-receptors (not β2), 2) cells from afflicted dogs display prolonged relaxation kinetics at long cycle lengths and large frequent spontaneous calcium oscillations (and aftercontractions) with little increase in calcium transient amplitude in response to β1-receptor agonists, and 3) β2-receptor agonists induce a similar marked increases in calcium transient and twitch amplitude, with only rare spontaneous calcium oscillations in afflicted and control cells. These results indicate that catecholamines provide inotropic support to canine cardiomyocytes through distinct β1- and β2-receptor pathways with differing requirements for cAMP. The propensity to develop arrhythmias is not induced by β2-receptors (or a rise in calcium alone), but rather occurs in the context of β1-receptor activation of the cAMP-dependent pathway.
Unloading-induced remodeling in the normal and hypertrophic left ventricle
Authors: McGowan Brian S. , Scott Christopher B. , Mu Anbin , McCormick Richard J. , Thomas D. Paul , Margulies Kenneth B.
Published: March 2015

To date, no study has assessed the degree of similarity between left ventricular (LV) reverse remodeling and atrophic remodeling. Stable LV hypertrophy was induced by creation of an arteriovenous fistula (AVF) in Lewis rats (32 days). LV unloading was induced by heterotopic transplantation of normal (NL-HT) and/or hypertrophic (AVF-HT) hearts (7 days). We compared indexes of remodeling in AVF, NL-HT, and AVF-HT groups with those of normal controls. LV unloading induced decreases in cardiomyocyte size in NL-HT and AVF-HT hearts. NL-HT and AVF-HT LV were both characterized by relative increases in collagen concentration that were largely a reflection of decreases in myocyte volume. NL-HT and AVF-HT LV were associated with similar increases in matrix metalloproteinase (MMP-2 and -9) zymographic activity, without change in the abundance of the tissue inhibitors of the MMPs. In contrast, AVF-HT, but not NL-HT, was associated with a dramatic increase in collagen cross-linking. Our findings suggest an overall similarity in the response of the normal and hypertrophic LV to surgical unloading. However, the dramatic increase in collagen cross-linking after just 1 wk of unloading suggests a potential difference in the dynamics of collagen metabolism between the two models. Further studies will be required to determine the precise molecular mechanisms responsible for these differences in extracellular matrix regulation. However, with respect to these and related issues, heterotopic transplantation of hypertrophied hearts will be a useful small animal model for defining mechanisms of myocyte-matrix interactions during decreased loading conditions.
Protective effect of melatonin on myocardial infarction
Authors: Chen Zhongyi , Chua Chu Chang , Gao Jinping , Hamdy Ronald C. , Chua Balvin H. L.
Published: March 2015

The dose- and time dependence of melatonin and the effective window of melatonin administration were determined in a mouse model of myocardial infarction. When mouse hearts were subjected to 60 min of occlusion of the left anterior descending artery (LAD) followed by 4 h of reperfusion, melatonin pretreatment for 30 min significantly reduced the infarct size/risk area. The most effective dose was found to be 150 μg/kg intraperitoneally, and the effective period of protection lasted up to 2 h after melatonin administration. Melatonin administration 45 min after LAD ligation or right before reperfusion was as effective as administration 30 min before ligation; however, melatonin administered after the release of occlusion was not protective. Melatonin's effect was still present in mice deficient for the Mel1a melatonin receptor. 8-Methoxy-2-propionamidotetralin, a melatonin receptor agonist with no antioxidant activity, offered no protection, suggesting a lack of involvement of melatonin receptors. Finally, the effects of melatonin were similar in rats and mice. Our results demonstrate that melatonin is an effective cardioprotective agent when administered either before or during coronary occlusion at a very low dose.
Infarct-induced chronic heart failure increases bidirectional protein movement across the alveolocapillary barrier
Authors: De Pasquale Carmine G. , Bersten Andrew D. , Doyle Ian R. , Aylward Phillip E. , Arnolda Leonard F.
Published: March 2015

Chronic heart failure (CHF) is associated with adaptive structural changes at the alveolocapillary barrier that may be associated with altered protein permeability. Bidirectional protein movement across the barrier was studied in anesthetized rats with infarct-induced CHF by following125I-labeled albumin (125I-albumin) flux into the alveoli and the leakage of surfactant protein (SP)-B from the alveoli into the circulation. Three groups were studied: controls [0% left ventricular (LV) infarction], moderate infarct (25–45% LV infarction), and large infarct (>46% LV infarction). Wet and dry lung weights increased in the large infarct group (both P < 0.001), consistent with increased lung water and solid lung tissue.125I-albumin flux increased across the endothelial ( P < 0.001) and epithelial ( P < 0.01) components of the alveolocapillary barrier in the large infarct group. Plasma SP-B increased 23% with moderate infarcts ( P < 0.05) and 97% with large infarcts ( P < 0.001), independent of alveolar levels. Lavage fluid immune cells ( P < 0.01) and myeloperoxidase activity ( P < 0.05) increased in the large infarct group, consistent with inflammation. Bidirectional protein movement across the alveolocapillary barrier is increased in CHF, and alveolar inflammation may contribute to this pathophysiological defect.
Carbon monoxide mediates vasodilator effects of glutamate in isolated pressurized cerebral arterioles of newborn pigs
Authors: Fiumana Elisa , Parfenova Helena , Jaggar Jonathan H. , Leffler Charles W.
Published: March 2015

The excitatory neurotransmitter glutamate causes dilation of newborn pig cerebral arterioles in vivo that is blocked by inhibition of carbon monoxide (CO) production. CO, a potent dilator in cerebral circulation in vivo, is produced endogenously in cerebral microvessels via heme oxygenase (HO). In isolated pressurized cerebral arterioles (∼200 μm) from newborn pigs, we investigated the involvement of CO and the endothelium in response to glutamate. A CO-releasing molecule, dimanganese decacarbonyl (10−8–10−6 M), dilated cerebral arterioles. Glutamate (10−6–10−4 M) and 1-aminocyclopentane- cis-1,3-dicarboxylic acid ( cis-ACPD; 10−6–10−5 M), a N-methyl-d-aspartate (NMDA) receptor agonist, caused cerebral vascular dilation. Dilation of cerebral arterioles to glutamate and cis-ACPD was abolished by chromium mesoporphyrin (CrMP; 10−6 M), a HO inhibitor. In contrast, CrMP did not alter dilation to isoproterenol, a β-adrenergic receptor agonist. Endothelium-denuded cerebral arterioles did not dilate to glutamate or bradykinin (endothelium-dependent dilator), whereas responses to isoproterenol were preserved. These data indicate that cerebral arterioles from newborn pigs may directly respond to glutamate and the NMDA receptor agonists by endothelium-dependent dilation that involves stimulation of CO production via the HO pathway in the endothelium.
Evidence of unbalanced regulatory mechanism of heart rate and systolic pressure after acute myocardial infarction
Authors: Nollo Giandomenico , Faes Luca , Porta Alberto , Pellegrini Barbara , Ravelli Flavia , Del Greco Maurizio , Disertori Marcello , Antolini Renzo
Published: March 2015

The interactions between systolic arterial pressure (SAP) and R-R interval (RR) fluctuations after acute myocardial infarction (AMI) were investigated by measures of synchronization separating the feedback from the feedforward control and capturing both linear and nonlinear contributions. The causal synchronization, evaluating the ability of RR to predict SAP (χs/t) or vice versa (χt/s), and the global synchronization (χ) were estimated at rest and after head-up tilt in 35 post-AMI patients, 20 young and 12 old. Significance and nonlinearity of the coupling were assessed by surrogate data analysis. Tilting increased the number of young subjects in which RR-SAP link was significant (from 17 to 19) and linear (from 11 to 18). In AMI, both significance and linearity of the coupling were low at rest (26 significant and 24 nonlinear) and further reduced after tilt (17 significant and 16 nonlinear). Old subjects showed a partial recovery of linearity after tilt (rest: 1 linear of 7 significant; tilt: 5 linear of 8 significant). In young subjects, the causal synchronization indexes were balanced and increased from rest (χt/s= 0.072 ± 0.037 and χs/t = 0.054 ± 0.028) to tilt (χt/s = 0.125 ± 0.071 and χs/t = 0.108 ± 0.053). On the contrary, in old subjects and AMI patients, the feedforward was prevalent to the feedback coupling at rest (old: χt/s = 0.041 ± 0.023 and χs/t = 0.069 ± 0.042; AMI: χt/s = 0.050 ± 0.030 and χs/t = 0.089 ± 0.053). Tilting blunted the unbalance in old subjects (χt/s = 0.065 ± 0.052 and χs/t = 0.069 ± 0.044) but not in AMI patients (χt/s = 0.040 ± 0.019 and χs/t = 0.060 ± 0.040). Thus, after AMI, nonlinear mechanisms are elicited in RR-SAP interactions. Furthermore, the neural regulation of the cardiovascular system resulted in imbalance as a consequence of impaired feedback and enhanced feedforward control mechanisms.
High agonist-independent clearance of rabbit kinin B1receptors in cultured cells
Authors: Fortin Jean-Philippe , Bouthillier Johanne , Marceau François
Published: March 2015

We hypothesized that the inducible kinin B1receptor (B1R) is rapidly cleared from cells when its synthesis subsides. The agonist-independent degradation of the rabbit B1Rs and related B2receptors (B2Rs) was investigated. Endocytosis of the B1R-yellow fluorescent protein (YFP) conjugate was more intense than that of B2R-green fluorescent protein (GFP) based on fluorescence accumulation in HEK 293 cells treated with a lysosomal inhibitor. The cells expressing B1R-YFP contained more GFP/YFP-sized degradation product(s) than those expressing B2R-GFP (immunoblot, antibodies equally reacting with both fluorescent proteins). The binding site density of B1R-YFP decreased in the presence of protein synthesis or maturation inhibitors (anisomycin, brefeldin A), whereas that of B2R-GFP remained constant. Wild-type B1Rs were also cleared faster than B2Rs in rabbit smooth muscle cells treated with metabolic inhibitors. Contractility experiments based on brefeldin A-treated isolated rabbit blood vessels also functionally support that B1Rs are more rapidly eliminated than B2Rs (decreased maximal effect of agonist over 2 h). The highly regulated B1R is rapidly degraded, relative to the constitutive B2R.