bluuebunny/crossref_metadata_2025 huggingface dataset:
Upregulation of neuronal nitric oxide synthase in skeletal muscle by swim training
Authors: Tatchum-Talom Rabelais , Schulz Richard , McNeill J. Robert , Khadour Fadi H.
Published: December 2017

Exercise enhances cardiac output and blood flow to working skeletal muscles but decreases visceral perfusion. The alterations in nitric oxide synthase (NOS) activity and/or expression of the cardiopulmonary, skeletal muscle, and visceral organs induced by swim training are unknown. In sedentary and swim-trained rats (60 min twice/day for 3–4 wk), we studied the alterations in NOS in different tissues along with hindquarter vasoreactivity in vivo during rest and mesenteric vascular bed reactivity in vitro. Hindquarter blood flow and conductance were reduced by norepinephrine in both groups to a similar degree, whereas N G-nitro-l-arginine methyl ester reduced both indexes to a greater extent in swim-trained rats. Vasodilator responses to ACh, but not bradykinin or S-nitroso- N-acetyl-penicillamine, were increased in swim-trained rats. Ca2+-dependent NOS activity was enhanced in the hindquarter skeletal muscle, lung, aorta, and atria of swim-trained rats together with increased expression of neuronal NOS in the hindquarter skeletal muscle and endothelial NOS in the cardiopulmonary organs. Mesenteric arterial bed vasoreactivity was unaltered by swim training. Physiological adaptations to swim training are characterized by enhanced hindquarter ACh-induced vasodilation with upregulation of neuronal NOS in skeletal muscle and endothelial NOS in the lung, atria, and aorta.
Mathematical analysis of canine atrial action potentials: rate, regional factors, and electrical remodeling
Authors: Ramirez Rafael J. , Nattel Stanley , Courtemanche Marc
Published: December 2017

Dogs have been used extensively to study atrial arrhythmias, but there are no published mathematical models of the canine atrial action potential (AP). To obtain insights into the ionic mechanisms governing canine atrial AP properties, we incorporated formulations of K+, Na+, Ca2+, and Cl− currents, based on measurements in canine atrial myocytes, into a mathematical model of the AP. The rate-dependent behavior of model APs corresponded to experimental measurements and pointed to a central role for L-type Ca2+ current inactivation in rate adaptation. Incorporating previously described regional ionic current variations into the model largely reproduced AP forms characteristic of the corresponding right atrial regions (appendage, pectinate muscle, crista terminalis, and atrioventricular ring). When ionic alterations induced by tachycardia-dependent remodeling were incorporated, the model reproduced qualitatively the AP features constituting the cellular substrate for atrial fibrillation. We conclude that this ionic model of the canine atrial AP agrees well with experimental measurements and gives potential insights into mechanisms underlying functionally important electrophysiological phenomena in canine atrium.
Angiotensin II acutely attenuates range of arterial baroreflex control of renal sympathetic nerve activity
Authors: Sanderford Max G. , Bishop Vernon S.
Published: December 2017

Acutely increasing peripheral angiotensin II (ANG II) reduces the maximum renal sympathetic nerve activity (RSNA) observed at low mean arterial blood pressures (MAPs). We postulated that this observation could be explained by the action of ANG II to acutely increase arterial blood pressure or increase circulating arginine vasopressin (AVP). Sustained increases in MAP and increases in circulating AVP have previously been shown to attenuate maximum RSNA at low MAP. In conscious rabbits pretreated with an AVP V1 receptor antagonist, we compared the effect of a 5-min intravenous infusion of ANG II (10 and 20 ng · kg−1 · min−1) on the relationship between MAP and RSNA when the acute pressor action of ANG II was left unopposed with that when the acute pressor action of ANG II was opposed by a simultaneous infusion of sodium nitroprusside (SNP). Intravenous infusion of ANG II resulted in a dose-related attenuation of the maximum RSNA observed at low MAP. When the acute pressor action of ANG II was prevented by SNP, maximum RSNA at low MAP was attenuated, similar to that observed when ANG II acutely increased MAP. In contrast, intravertebral infusion of ANG II attenuated maximum RSNA at low MAP significantly more than when administered intravenously. The results of this study suggest that ANG II may act within the central nervous system to acutely attenuate the maximum RSNA observed at low MAP.
Role of pertussis toxin-sensitive G protein in metabolic vasodilation of coronary microcirculation
Authors: Tanikawa Toshinori , Kanatsuka Hiroshi , Koshida Ryohji , Tanaka Mitsuaki , Sugimura Akihiko , Kumagai Toshinobu , Miura Masahito , Komaru Tatsuya , Shirato Kunio
Published: December 2017

We have previously demonstrated that pertussis toxin (PTX)-sensitive G protein (GPTX) plays a major role in coronary microvascular vasomotion during hypoperfusion. We aimed to elucidate the role of GPTX during increasing metabolic demand. In 18 mongrel dogs, coronary arteriolar diameters were measured by fluorescence microangiography using a floating objective. Myocardial oxygen consumption (MV˙o 2) was increased by rapid left atrial pacing. In six dogs, PTX (300 ng/ml) was superfused onto the heart surface for 2 h to locally block GPTX. In eight dogs, the vehicle (Krebs solution) was superfused in the same way. Before and after each treatment, the diameters were measured during control (130 beats/min) and rapid pacing (260 beats/min) in each group. Metabolic stimulation before and after the vehicle treatment caused 8.6 ± 1.8 and 16.1 ± 3.6% dilation of coronary arterioles <100 μm in diameter (57 ± 8 μm at control, n = 10), respectively. PTX treatment clearly abolished the dilation of arterioles (12.8 ± 2.5% before and 0.9 ± 1.6% after the treatment, P < 0.001 vs. vehicle; 66 ± 8 μm at control, n = 11) in response to metabolic stimulation. The increases in MV˙o 2 and coronary flow velocity were comparable between the vehicle and PTX groups. In four dogs, 8-phenyltheophylline (10 μM, superfusion for 30 min) did not affect the metabolic dilation of arterioles (15.3 ± 2.0% before and 16.4 ± 3.8% after treatment; 84.3 ± 11.0 μm at control, n = 8). Thus we conclude that GPTXplays a major role in regulating the coronary microvascular tone during active hyperemia, and adenosine does not contribute to metabolic vasodilation via GPTX activation.
Flumazenil preconditions cardiomyocytes via oxygen radicals and KATPchannels
Authors: Zhang Qiang , Yao Zhenhai
Published: December 2017

We determined whether flumazenil mimics ischemic preconditioning in chick cardiomyocytes and examined the role of intracellular reactive oxygen species (ROS) and ATP-dependent potassium (KATP) channels in mediating the effect. Chick ventricular myocytes were perfused with a balanced salt solution in a flow-through chamber. Cell viability was quantified using propidium iodide, and ROS generation was assessed using the reduced form of 2′,7′-dichlorofluorescin (DCFH). Cells were exposed to 1 h of simulated ischemia and 3 h of reoxygenation. Preconditioning was initiated with 10 min of ischemia followed by 10 min of reoxygenation. Alternatively, flumazenil was added to the perfusate for 10 min and removed 10 min before the start of ischemia. Flumazenil (1 and 10 μM) and preconditioning reduced cell death [54 ± 5%, n = 3; 26 ± 4%, n = 6 ( P < 0.05); and 20 ± 2%, n = 6 (P < 0.05), respectively, vs. 57 ± 7%, n = 10, in controls] and increased DCFH oxidation (an index of ROS production) [0.35 ± 0.11, n = 3; 2.64 ± 0.69, n = 8 ( P < 0.05); and 2.46 ± 0.52, n = 6 ( P< 0.05), respectively, vs. 0.26 ± 0.05, n = 9, in controls]. Protection and increased ROS signals with flumazenil (10 μM) were abolished with the thiol reductant N-(2-mercaptopropionyl)-glycine (2-MPG, 800 μM), an antioxidant (cell death: 2-MPG + flumazenil, 55 ± 12%, n = 6; ROS signals: 2-MPG + flumazenil, 0.11 ± 0.19, n = 6). Treatment with 5-hydroxydecanoate (1 mM), a selective mitochondrial KATPchannel antagonist, abolished its protection. These results demonstrate that flumazenil mimics preconditioning to reduce cell death in myocytes. ROS signals with the resultant mitochondrial KATPchannel activation are important components of the intracellular signaling pathway of flumazenil.
Carotid baroreflex responsiveness in heat-stressed humans
Authors: Crandall C. G.
Published: December 2017

The effects of whole body heating on human baroreflex function are relatively unknown. The purpose of this project was to identify whether whole body heating reduces the maximal slope of the carotid baroreflex. In 12 subjects, carotid-vasomotor and carotid-cardiac baroreflex responsiveness were assessed in normothermia and during whole body heating. Whole body heating increased sublingual temperature (from 36.4 ± 0.1 to 37.4 ± 0.1°C, P < 0.01) and increased heart rate (from 59 ± 3 to 83 ± 3 beats/min, P < 0.01), whereas mean arterial blood pressure (MAP) was slightly decreased (from 88 ± 2 to 83 ± 2 mmHg, P < 0.01). Carotid-vasomotor and carotid-cardiac responsiveness were assessed by identifying the maximal gain of MAP and heart rate to R wave-triggered changes in carotid sinus transmural pressure. Whole body heating significantly decreased the responsiveness of the carotid-vasomotor baroreflex (from −0.20 ± 0.02 to −0.13 ± 0.02 mmHg/mmHg, P < 0.01) without altering the responsiveness of the carotid-cardiac baroreflex (from −0.40 ± 0.05 to −0.36 ± 0.02 beats · min−1 · mmHg−1, P = 0.21). Carotid-vasomotor and carotid-cardiac baroreflex curves were shifted downward and upward, respectively, to accommodate the decrease in blood pressure and increase in heart rate that accompanied the heat stress. Moreover, the operating point of the carotid-cardiac baroreflex was shifted closer to threshold ( P = 0.02) by the heat stress. Reduced carotid-vasomotor baroreflex responsiveness, coupled with a reduction in the functional reserve for the carotid baroreflex to increase heart rate during a hypotensive challenge, may contribute to increased susceptibility to orthostatic intolerance during a heat stress.
Differential effects of l-NAME on rat venular hydraulic conductivity
Authors: Rumbaut Rolando E. , Wang Jianjie , Huxley Virginia H.
Published: December 2017

The role of nitric oxide (NO) in microvascular permeability remains unclear because both increases and decreases in permeability by NO synthase (NOS) inhibitors have been reported. We sought to determine whether blood-borne constituents modify venular permeability responses to the NOS inhibitor N G-nitro-l-arginine methyl ester (l-NAME). We assessed hydraulic conductivity ( L p) of pipette-perfused rat mesenteric venules before and after exposure to 10−4 M l-NAME. In the absence of blood-borne constituents, l-NAME reduced L p by nearly 50% (from a median of 2.4 × 10−7cm · s−1 · cmH2O−1, n = 17, P < 0.001). The reduction in L p by l-NAME was inhibited by a 10-fold molar excess of l-arginine but notd-arginine ( n = 6). In a separate group of venules, blood flow was allowed to resume during exposure tol-NAME. In vessels perfused by blood duringl-NAME exposure, L p increased by 78% (from 1.4 × 10−7cm · s−1 · cmH2O−1, n = 10, P < 0.01). N G-nitro-d-arginine methyl ester did not affect L p in either of the two groups. These data imply that NO has direct vascular effects on permeability that are opposed by secondary changes in permeability mediated by blood-borne constituents.
Increased medial smooth muscle cell length is responsible for vascular hypertrophy in young hypertensive rats
Authors: Dickhout J. G. , Lee R. M. K. W.
Published: December 2017

Large mesenteric arteries from 3- to 4-wk-old spontaneously hypertensive rats (SHR) showed medial hypertrophy and an increased contractile response to various agonists before significant blood pressure increase. Here we determined the cellular nature of this vascular hypertrophy. Large mesenteric arteries from SHR and Wistar-Kyoto (WKY) rats were fixed at maximal relaxation either with an in situ perfusion fixation or an in vitro fixation method. With the use of morphometric protocols and confocal microscopy, the volume of the medial wall and lumen, numerical density of smooth muscle cell nuclei in the medial layer, and smooth muscle cell and nuclear length were measured. Both methods of fixation yielded similar results, showing significant medial volume expansion in SHR than WKY without lumen change. Numerical density of medial smooth muscle cells was significantly less in SHR than WKY, and their total number per 100 μm length were similar between the strains. Average smooth muscle nuclear and cell length from SHR was significantly longer than that of WKY. Regression analysis showed that the increase in smooth muscle cell length explained 80% of the medial volume increase. We concluded that increased smooth muscle cell length in prehypertensive SHR is responsible for increased medial volume in the mesenteric arteries.
Fast pacing facilitates discontinuous action potential propagation between rabbit atrial cells
Authors: Wang Yang-Gan , Wagner Mary B. , Kumar Rajiv , Goolsby William N. , Joyner Ronald W.
Published: December 2017

We examined the critical coupling conductance ( G C) for propagation at different pacing cycle lengths (CLs) (1,000 and 400 ms). As G C was progressively reduced, propagation failed at a CL of 1,000 ms, whereas propagation succeeded at a CL of 400 ms over a range of G C values before failing at a CL of 400 ms at a lower G C, showing facilitation of propagation at the shorter CL. Critical G C was (means ± SE) 0.8 ± 0.1 nS for a CL of 400 ms and 1.3 ± 0.1 nS for a CL of 1,000 ms (a 63% increase, P < 0.002, n = 9 cell pairs). In 14 uncoupled cells, action potential duration at 30% repolarization (APD30) increased from 19.9 ± 2.5 to 41.8 ± 2.6 ms ( P < 0.001) as CL decreased from 1,000 to 400 ms. In five cell pairs, critical G Cwith 4-aminopyridine (4-AP) was reduced to 0.4 ± 0.1 nS at a CL of 1,000 ms ( P < 0.05 compared with control solution), and critical G C in 4-AP was unchanged by decreasing CL to 400 ms. It is possible that the “remodeling” of atrial cells due to atrial fibrillation or tachycardia, which has been shown to produce a decrease in the transient outward current, may result in an enhanced ability to propagate, possibly facilitating further development of fibrillation under conditions of decreased cellular coupling.
Intrinsic A1 adenosine receptor activation during ischemia or reperfusion improves recovery in mouse hearts
Authors: Peart Jason , Headrick John P.
Published: December 2017

We assessed the role of A1 adenosine receptor (A1AR) activation by endogenous adenosine in the modulation of ischemic contracture and postischemic recovery in Langendorff-perfused mouse hearts subjected to 20 min of total ischemia and 30 min of reperfusion. In control hearts, the rate-pressure product (RPP) and first derivative of pressure development over time (+dP/d t) recovered to 57 ± 3 and 58 ± 3% of preischemia, respectively. Diastolic pressure remained elevated at 20 ± 2 mmHg (compared with 3 ± 1 mmHg preischemia). Interstitial adenosine, assessed by microdialysis, rose from ∼0.3 to 1.9 μM during ischemia compared with ∼15 μM in rat heart. Nonetheless, these levels will near maximally activate A1ARs on the basis of effects of exogenous adenosine and 2-chloroadenosine. Neither A1AR blockade with 200 nM 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) during the ischemic period alone nor A1AR activation with 50 nM N 6-cyclopentyladenosine altered rapidity or extent of ischemic contracture. However, ischemic DPCPX treatment significantly depressed postischemic recovery of RPP and +dP/d t (44 ± 3 and 40 ± 4% of preischemia, respectively). DPCPX treatment during the reperfusion period alone also reduced recovery of RPP and +dP/d t (to 44 ± 2 and 47 ± 2% of preischemia, respectively). These data indicate that 1) interstitial adenosine is lower in mouse versus rat myocardium during ischemia, 2) A1AR activation by endogenous adenosine or exogenous agonists does not modify ischemic contracture in murine myocardium, 3) A1AR activation by endogenous adenosine during ischemia attenuates postischemic stunning, and 4) A1AR activation by endogenous adenosine during the reperfusion period also improves postischemic contractile recovery.
Oxidative stress impairs cardiac chemoreflexes in diabetic rats
Authors: Ustinova Elena E. , Barrett Carolyn J. , Sun Shu-Yu , Schultz Harold D.
Published: December 2017

We investigated the effects of diabetes mellitus and antioxidant treatment on the sensory and reflex function of cardiac chemosensory nerves in rats. Diabetes was induced by streptozotocin (STZ; 85 mg/kg ip). Subgroups of sham- and STZ-treated rats were chronically treated with an antioxidant, vitamin E (60 mg/kg per os daily, started 2 days before STZ). Animals were studied 6–8 wk after STZ injection. We measured renal sympathetic nerve activity (RSNA), mean arterial blood pressure (MABP), and cardiac vagal and sympathetic afferent activities in response to stimulation of chemosensitive sensory nerves in the heart by epicardial application of capsaicin (Caps) and bradykinin (BK). In cardiac sympathetic-denervated rats, Caps and BK (1–10.0 μg) evoked a vagal afferent mediated reflex depression of RSNA and MABP, which was significantly blunted in STZ-treated rats ( P < 0.05). In vagal-denervated rats, Caps and BK (1–10.0 μg) evoked a sympathetic afferent-mediated reflex elevation of RSNA and MABP, which also was significantly blunted in STZ-treated rats ( P< 0.05). Chronic vitamin E treatment effectively prevented these cardiac chemoreflex defects in STZ-treated rats without altering resting blood glucose or hemodynamics. STZ-treated rats with insulin replacement did not exhibit impaired cardiac chemoreflexes. In afferent studies, Caps and BK (0.1 g-10.0 μg) increased cardiac vagal and sympathetic afferent nerve activity in a dose-dependent manner in sham-treated rats. These responses were significantly blunted in STZ-treated rats. Vitamin E prevented the impairment of afferent discharge to chemical stimulation in STZ rats. The following were concluded: STZ-induced, insulin-dependent diabetes in rats extensively impairs the sensory and reflex properties of cardiac chemosensitive nerve endings, and these disturbances can be prevented by chronic treatment with vitamin E. These results suggest that oxidative stress plays an important role in the neuropathy of this autonomic reflex in diabetes.
Dependence of intestinal arteriolar regulation on flow-mediated nitric oxide formation
Authors: Bohlen H. Glenn , Nase Geoffrey P.
Published: December 2017

Our hypothesis was that a large fraction of resting nitric oxide (NO) formation is driven by flow-mediated mechanisms in the intestinal microvasculature of the rat. NO-sensitive microelectrodes measured the in vivo perivascular NO concentration ([NO]). Flow was increased by forcing the arterioles to perfuse additional nearby arterioles; flow was decreased by lowering the mucosal metabolic rate by reducing sodium absorption. Resting periarteriolar [NO] of large arterioles (first order; 1A) and intermediate-sized arterioles (second order; 2A) was 337 ± 20 and 318 ± 21 nM. The resting [NO] was higher than the dissociation constant for the NO-guanylate cyclase reaction of vascular smooth muscle; therefore, resting [NO] should be a potent dilatory signal at rest. Over flow velocity and shear rate ranges of ∼40–180% of control, periarteriolar [NO] changed 5–8% for each 10% change in flow velocity and shear rate. The relationship of [NO] to flow velocity and shear rate demonstrated that 60–80% of resting [NO] depended on flow-mediated mechanisms. Therefore, moment-to-moment regulation of [NO] at rest is an ongoing process that is highly dependent on flow-dependent mechanisms.
Differential role of KATP channels in late preconditioning against myocardial stunning and infarction in rabbits
Authors: Takano Hitoshi , Tang Xian-Liang , Bolli Roberto
Published: December 2017

The role of ATP-sensitive potassium (KATP) channels in the late phase of ischemic preconditioning (PC) remains unclear. Furthermore, it is unknown whether KATP channels serve as end effectors both for late PC against infarction and against stunning. Thus, in phase I of this study, conscious rabbits underwent a 30-min coronary occlusion (O) followed by 72 h of reperfusion (R) with or without ischemic PC (6 4-min O/4-min R cycles) 24 h earlier. Late PC reduced infarct size ∼46% versus controls. The KATPchannel blocker 5-hydroxydecanoic acid (5-HD), given 5 min before the 30-min O, abrogated the infarct-sparing effect of late PC but did not alter infarct size in non-PC rabbits. In phase II, rabbits underwent six 4-min O/4-min R cycles for 3 consecutive days ( days 1, 2, and 3). In controls, the total deficit of systolic wall thickening (WTh) after the sixth reperfusion was reduced by 46% on day 2 and 54% on day 3compared with day 1, indicating a late PC effect against myocardial stunning. Neither 5-HD nor glibenclamide, given on day 2, abrogated late PC. The KATP channel opener diazoxide, given on day 1, attenuated stunning, and this effect was completely blocked by 5-HD. Thus the same dose of 5-HD that blocked the antistunning effect of diazoxide failed to block the antistunning effects of late PC. Furthermore, when diazoxide was administered in PC rabbits on day 2, myocardial stunning was further attenuated, indicating that diazoxide and late PC have additive anti-stunning effects. We conclude that KATP channels play an essential role in late PC against infarction but not in late PC against stunning, revealing an important pathogenetic difference between these two forms of cardioprotection.
Active and passive stresses in the myocardium
Authors: Shoucri Rachad M.
Published: December 2017

A mathematical approach that can be used to calculate the passive stress in the ventricular wall is presented. The active fiber stress (force/unit area) generated by the muscular fibers in the ventricular wall is expressed by means of body force (force/unit volume of the myocardium). It is shown that the total intramyocardial passive stress induced in the passive medium of the myocardium can be expressed as the sum of a passive stress induced by the left ventricular pressure and a passive stress induced by the active fiber stress. Applications to experimental data published in the literature are given. New results are presented that show the relation among those two components of the intramyocardial passive stress. New relations between the intramyocardial passive stress, the slope (elastance) of the pressure-volume relation, and the residual volume are also derived. The results obtained give a better understanding of some aspects of the mechanics of cardiac contraction and can provide a more detailed interpretation of clinical conditions.
Human coronary arteriolar dilation to adrenomedullin: role of nitric oxide and K+ channels
Authors: Terata Ken , Miura Hiroto , Liu Yanping , Loberiza Fausto , Gutterman David D.
Published: December 2017

Adrenomedullin (ADM) is a vasodilator produced by vascular endothelium and smooth muscle cells. Although plasma ADM levels are increased in patients with hypertension, heart failure, and myocardial infarction, little information exists regarding the microvascular response to ADM in the human heart. In the present study we tested the hypothesis that ADM produces coronary arteriolar dilation in humans and examined the mechanism of this dilation. Human coronary arterioles were dissected and cannulated with micropipettes. Internal diameter was measured by video microscopy. In vessels constricted with ACh, the diameter response to cumulative doses of ADM (10−12–10−7 M) was measured in the presence and absence of human ADM-(22–52), calcitonin gene-related peptide-(8–37), N ω-nitro-l-arginine methyl ester (l-NAME), indomethacin (Indo),1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, SQ-22536, or KCl (60 mM). ADM dilated human coronary arterioles through specific ADM receptors (maximum dilation = 69 ± 11%).l-NAME or N-monomethyl-l-arginine attenuated dilation to ADM (for l-NAME, maximum dilation = 66 ± 7 vs. 41 ± 13%, P < 0.05). Thus the mechanism of ADM-induced dilation involves generation of nitric oxide. However, neither1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, SQ-22536, nor Indo alone altered dilation to ADM. High concentrations of KCl blocked dilation to ADM. The magnitude of ADM dilation was reduced in subjects with hypertension. We propose that, in human coronary arterioles, ADM elicits vasodilation in part through production of nitric oxide and in part through activation of K+ channels, with little contribution from adenylyl cyclase. The former dilator mechanism is independent of the more traditional pathway involving activation of soluble guanylate cyclase.
Effects of [K+]o on electrical restitution and activation dynamics during ventricular fibrillation
Authors: Koller Marcus L. , Riccio Mark L. , Gilmour Robert F.
Published: December 2017

To test whether hyperkalemia suppresses ventricular fibrillation (VF) by reducing the slope of the action potential duration (APD) restitution relation, we determined the effects of the extracellular K+concentration ([K+]o) ([KCl] = 2.7–12 mM) on the restitution of APD and maximum upstroke velocity ( V max) the magnitude of APD alternans and spatiotemporal organization during VF in isolated canine ventricle. As [KCl] was increased incrementally from 2.7 to 12 mM, V max was reduced progressively. Increasing [KCl] from 2.7 to 10 mM decreased the slope of the APD restitution relation at long, but not short, diastolic intervals (DI), decreased the range of DI over which the slope was ≥1, and reduced the maximum amplitude of APD alternans. At [KCl] = 12 mM, the range of DI over which the APD restitution slope was ≥1 increased, and the maximum amplitude of APD alternans increased. For [KCl] = 4–8 mM, the persistence of APD alternans at short DI was associated with maintenance of VF. For [KCl] = 10–12 mM, the spontaneous frequency during VF was reduced, and activation occurred predominantly at longer DI. The lack of APD alternans at longer DI was associated with conversion of VF to a periodic rhythm. These results provide additional evidence for the importance of APD restitution kinetics in the development of VF.
NOC/oFQ PKC-dependent superoxide generation contributes to hypoxic-ischemic impairment of NMDA cerebrovasodilation
Authors: Armstead William M.
Published: December 2017

This study determined whether nociceptin/orphanin FQ (NOC/oFQ) generates superoxide anion (O2 −) in a protein kinase C (PKC)-dependent manner and whether such production contributes to hypoxic-ischemic (H-I) impairment of N-methyl-d-aspartate (NMDA)-induced pial artery dilation in newborn pigs equipped with closed cranial windows. Superoxide dismutase (SOD)-inhibitable nitroblue tetrazolium (NBT) reduction was an index of O2 − generation. Under non-H-I conditions, topical NOC/oFQ (10−10 M, concentration present in cerebrospinal fluid after I or H-I) increased SOD-inhibitable NBT reduction from 1 ± 1 to 20 ± 3 pmol/mm2. PKC inhibitors staurosporine and chelerythrine (10−7 M) blunted NBT reduction (1 ± 1 to 7 ± 2 pmol/mm2 for chelerythrine), whereas the NOC/oFQ receptor antagonist [F/G]NOC/oFQ (1–13)-NH2(10−6 M) blocked NBT reduction. [F/G]NOC/oFQ(1–13)-NH2 and staurosporine also blunted the NBT reduction observed after I or H-I. NMDA (10−8, 10−6 M)-induced pial artery dilation was reversed to vasoconstriction after H-I. The NOC/oFQ antagonist staurosporine and free radical scavengers partially prevented this impaired dilation (sham: 9 ± 1 and 16 ± 1; H-I: −5 and −10 ± 1; H-I staurosporine pretreated: 3 ± 1 and 6 ± 1%). These data show that NOC/oFQ increased O2 − production in a PKC-dependent manner and contributed to this production after insult and that NOC/oFQ contributed to impaired NMDA-induced pial artery dilation after H-I, suggesting, therefore, that PKC-dependent O2 −generation by NOC/oFQ links NOC/oFQ release to impaired NMDA dilation after H-I.
Role for PKC in the adenosine-induced decrease in shortening velocity of rat ventricular myocytes
Authors: Lester J. William , Hofmann Polly A.
Published: December 2017

We previously demonstrated that both adenosine receptor activation and direct activation of protein kinase C (PKC) decrease unloaded shortening velocity ( Vmax) of rat ventricular myocytes. The goal of this study was to further investigate a possible link among adenosine receptors, phosphoinositide-PKC signaling, and Vmaxin rat ventricular myocytes. We determined that the adenosine receptor agonist R-phenylisopropyladenosine ( R-PIA, 100 μM) and the α-adrenergic receptor agonist phenylephrine (Phe, 10 μM) increased turnover of inositol phosphates. PKC translocation from the cytosol to the sarcolemma was used as an indicator of PKC activation. Western blot analysis demonstrated an increased PKC-ɛ translocation after exposure to R-PIA, Phe, and the PKC activators dioctanoylglycerol (50 μM) and phorbol myristate acetate (1 μM). PKC-α, PKC-δ, and PKC-ζ did not translocate to the membrane after R-PIA exposure. Finally, PKC inhibitors blocked R-PIA-induced decreases in Vmaxas well as Ca2+-dependent actomyosin ATPase in rat ventricular myocytes. These results support the conclusions that adenosine receptors activate phosphoinositide-PKC signaling and that adenosine receptor-induced PKC activation mediates a decrease in Vmaxin ventricular myocytes.
Differential role of sarcolemmal and mitochondrial KATPchannels in adenosine-enhanced ischemic preconditioning
Authors: Toyoda Yoshiya , Friehs Ingeborg , Parker Robert A. , Levitsky Sidney , McCully James D.
Published: December 2017

Adenosine-enhanced ischemic preconditioning (APC) extends the protection afforded by ischemic preconditioning (IPC) by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. The purpose of this study was to determine whether APC is modulated by ATP-sensitive potassium (KATP) channels and to determine whether this modulation occurs before ischemia or during reperfusion. The role of KATPchannels before ischemia (I), during reperfusion (R), or during ischemia and reperfusion (IR) was investigated using the nonspecific KATPblocker glibenclamide (Glb), the mitochondrial (mito) KATPchannel blocker 5-hydroxydecanoate (5-HD), and the sarcolemmal (sarc) KATPchannel blocker HMR-1883 (HMR). Infarct size was significantly increased ( P < 0.05) in APC hearts with Glb-I, Glb-R, and 5-HD-I treatment and partially with 5-HD-R. Glb-I and Glb-R treatment significantly decreased APC functional recovery ( P < 0.05 vs. APC), whereas 5-HD-I and 5-HD-R had no effect on APC functional recovery. HMR-IR significantly decreased postischemic functional recovery ( P < 0.05 vs. APC) but had no effect on infarct size. These data indicate that APC infarct size reduction is modulated by mitoKATPchannels primarily during ischemia and suggest that functional recovery is modulated by sarcKATPchannels during ischemia and reperfusion.
Improved cardiac contractile functions in hypoxia-reoxygenation in rats treated with low concentration Co2+
Authors: Endoh Hiroshi , Kaneko Takaho , Nakamura Hiro , Doi Katsuhiko , Takahashi Eiji
Published: December 2017

An intracellular mechanism that senses decreases in tissue oxygen level and stimulates hypoxia-related gene expression has been reported in various cell types including the cardiac cell. The mechanism can also be activated by Co2+in normoxia. Thus we investigated the effects of prior chronic oral CoCl2on mechanical functions of isolated, perfused rat hearts in hypoxia-reoxygenation. In normoxic rats, 43 days of Co2+administration increased hematocrit from 45 ± 0.3% (control, n = 18) to 51 ± 0.6% ( n = 19). In hypoxia and reoxygenation, Co2+-pretreated hearts exhibited a significantly higher rate-pressure product (267 and 163%, respectively) and coronary flow (127 and 118%, respectively) and lower end-diastolic pressure (72 and 60%, respectively) compared with the control hearts. Although the oral Co2+administration significantly raised myocardial Co2+concentration, it did not affect mitochondrial respiration, tissue glycogen concentration, or myocardial tissue histology. The levels of vascular endothelial growth factor, aldolase-A, and glucose transporter-1 mRNA were significantly elevated in the Co2+-treated myocardium. We conclude that cardiac contractile functions would gain hypoxic tolerance when the endogenous cellular oxygen-sensing mechanism is activated.
Mechanisms by which bradykinin promotes fibrosis in vascular smooth muscle cells: role of TGF-β and MAPK
Authors: Douillet Christelle D. , Velarde Victoria , Christopher Julie T. , Mayfield Ronald K. , Trojanowska Maria E. , Jaffa Ayad A.
Published: December 2017

Accumulation of extracellular matrix (ECM) is a hallmark feature of vascular disease. We have previously shown that hyperglycemia induces the expression of B2-kinin receptors in vascular smooth muscle cells (VSMC) and that bradykinin (BK) and hyperglycemia synergize to stimulate ECM production. The present study examined the cellular mechanisms through which BK contributes to VSMC fibrosis. VSMC treated with BK (10−8 M) for 24 h significantly increased α2(I) collagen mRNA levels. In addition, BK produced a two- to threefold increase in α2(I) collagen promoter activity in VSMC transfected with a plasmid containing the α2(I) collagen promoter. Furthermore, treatment of VSMC with BK for 24 h produced a two- to threefold increase in the secretion rate of tissue inhibitor of metalloproteinase 1 (TIMP-1). The increase in α2(I) collagen mRNA levels and α2(I) collagen promoter activity, as well as TIMP-1 secretion, in response to BK were blocked by anti-transforming growth factor-β (anti-TGF-β) neutralizing antibodies. BK (10−8 M) increased the endogenous production of TGF-β1 mRNA and protein levels. Inhibition of the mitogen-activated protein kinase (MAPK) pathway by PD-98059 inhibited the increase of α2(I) collagen promoter activity, TIMP-1 production, and TGF-β1 protein levels observed in response to BK. These findings provide the first evidence that BK induces collagen type I and TIMP-1 production via autocrine activation of TGF-β1 and implicate MAPK pathway as a key player in VSMC fibrosis in response of BK.
Low [Mg2+]oinduces contraction and [Ca2+]irises in cerebral arteries: roles of Ca2+, PKC, and PI3
Authors: Yang Zhi-Wei , Wang Jun , Zheng Tao , Altura Bella T. , Altura Burton M.
Published: December 2017

Removal of extracellular Ca2+concentration ([Ca2+]o) and pretreatment of canine basilar arterial rings with either an antagonist of voltage-gated Ca2+channels (verapamil), a selective antagonist of the sarcoplasmic reticulum Ca2+pump [thapsigargin (TSG)], caffeine plus a specific antagonist of ryanodine-sensitive Ca2+release (ryanodine), or ad- myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]- mediated Ca2+release antagonist (heparin) markedly attenuates low extracellular Mg2+concentration ([Mg2+]o)-induced contractions. Low [Mg2+]o-induced contractions are significantly inhibited by pretreatment of the vessels with Gö-6976 [a protein kinase C-α (PKC-α)- and PKC-βI-selective antagonist], bisindolylmaleimide I (Bis, a specific antagonist of PKC), and wortmannin or LY-294002 [selective antagonists of phosphatidylinositol-3 kinases (PI3Ks)]. These antagonists were also found to relax arterial contractions induced by low [Mg2+]oin a concentration-dependent manner. The absence of [Ca2+]oand preincubation of the cells with verapamil, TSG, heparin, or caffeine plus ryanodine markedly attenuates the transient and sustained elevations in the intracellular Ca2+concentration ([Ca2+]i) induced by low-[Mg2+]omedium. Low [Mg2+]o-produced increases in [Ca2+]iare also suppressed markedly in the presence of Gö-6976, Bis, wortmannin, or LY-294002. The present study suggests that both Ca2+influx through voltage-gated Ca2+channels and Ca2+release from intracellular stores [both Ins(1,4,5)P3sensitive and ryanodine sensitive] play important roles in low-[Mg2+]omedium-induced contractions of isolated canine basilar arteries. Such contractions are clearly associated with activation of PKC isoforms and PI3Ks.
Spinotrapezius muscle microcirculatory function: effects of surgical exteriorization
Authors: Bailey Janet K. , Kindig Casey A. , Behnke Brad J. , Musch Timothy I. , Schmid-Schoenbein Geert W. , Poole David C.
Published: December 2017

Intravital microscopy facilitates insights into muscle microcirculatory structural and functional control, provided that surgical exteriorization does not impact vascular function. We utilized a novel combination of phosphorescence quenching, microvascular oxygen pressure (microvascular Po 2), and microsphere (blood flow) techniques to evaluate static and dynamic behavior within the exposed intact (I) and exteriorized (EX) rat spinotrapezius muscle. I and EX muscles were studied under control, metabolic blockade with 2,4-dinitrophenol (DNP), and electrically stimulated conditions with 1-Hz contractions, and across switches from 21 to 100% and 10% inspired O2. Surgical preparation did not alter spinotrapezius muscle blood flow in either I or EX muscle. DNP elevated muscle blood flow ∼120% ( P < 0.05) in both I and EX muscles ( P> 0.05 between I and EX). Contractions reduced microvascular Po 2 from 30.4 ± 4.3 to 21.8 ± 4.8 mmHg in I muscle and from 33.2 ± 3.0 to 25.9 ± 2.8 mmHg in EX muscles with no difference between I and EX. In each O2condition, there was no difference (each P > 0.05) in microvascular Po 2 between I and EX muscles (21% O2: I = 37 ± 1; EX = 36 ± 1; 100%: I = 62 ± 5; EX = 51 ± 9; 10%: I = 20 ± 1; EX = 17 ± 2 mmHg). Similarly, the dynamic behavior of microvascular Po 2 to altered inspired O2 was unaffected by the EX procedure [half-time ( t 1/2) to 100% O2: I = 23 ± 5; EX = 23 ± 4; t 1/2 to 10%: I = 14 ± 2; EX = 16 ± 2 s, both P > 0.05]. These results demonstrate that the spinotrapezius muscle can be EX without significant alteration of microvascular integrity and responsiveness under the conditions assessed.
α-Adrenoceptor stimulation-mediated negative inotropism and enhanced Na+/Ca2+ exchange in mouse ventricle
Authors: Nishimaru Kazuhide , Kobayashi May , Matsuda Tomoyuki , Tanaka Yoshio , Tanaka Hikaru , Shigenobu Koki
Published: December 2017

Mechanisms underlying the negative inotropic response to α-adrenoceptor stimulation in adult mouse ventricular myocardium were studied. In isolated ventricular tissue, phenylephrine (PE), in the presence of propranolol, decreased contractile force by ∼40% of basal value. The negative inotropic response was similarly observed under low extracellular Ca2+ concentration ([Ca2+]o) conditions but was significantly smaller under high-[Ca2+]o conditions and was not observed under low-[Na+]o conditions. The negative inotropic response was not affected by nicardipine, ryanodine, ouabain, or dimethylamiloride (DMA), inhibitors of L-type Ca2+ channel, Ca2+ release channel, Na+-K+ pump, or Na+/H+exchanger, respectively. KB-R7943, an inhibitor of Na+/Ca2+ exchanger, suppressed the negative inotropic response mediated by PE. PE reduced the magnitude of postrest contractions. PE caused a decrease in duration of the late plateau phase of action potential and a slight increase in resting membrane potential; time courses of these effects were similar to that of the negative inotropic effect. In whole cell voltage-clamped myocytes, PE increased the L-type Ca2+ and Na+/Ca2+ exchanger currents but had no effect on the inwardly rectifying K+, transient outward K+, or Na+-K+-pump currents. These results suggest that the sustained negative inotropic response to α-adrenoceptor stimulation of adult mouse ventricular myocardium is mediated by enhancement of Ca2+ efflux through the Na+/Ca2+ exchanger.
Minimal protection of the liver by ischemic preconditioning in pigs
Authors: Schulz Rainer , Walz Martin K. , Behrends Matthias , Neumann Till , Gerken Guido , Heusch Gerd
Published: December 2017

Ischemic preconditioning (IP) protects the rat liver. In pigs, in which hepatic tolerance to ischemia is similar to that in humans, information on IP is lacking. Therefore, in enflurane-anesthetized pigs, hepatic vessels were occluded for 120 min ( protocol 1) or 200 min ( protocol 2) without (control) and with IP (3 times 10 min ischemia-reperfusion each). In protocol 1, cumulative bile flow (CBF) during reperfusion was greater in IP (47.3 ± 5.2 ml/8 h) than in control (17.1 ± 7.8 ml/8 h, P < 0.05). ATP content tended to recover toward normal during reperfusion in IP, whereas it remained at ischemic levels in control. Serum enzyme concentrations increased similarly during reperfusion, and <1% hepatocytes were necrotic or stained terminal deosynucleotidyl transferase-mediated dUTP nick-end labeling-positive in control and IP groups. In protocol 2, no differences in CBF, ATP, or serum enzyme concentrations during reperfusion were measured between control and IP groups, except for a somewhat reduced lactate dehydrogenase in IP. The number of necrotic or terminal deosynucleotidyl transferase-mediated dUTP nick-end labeling-positive hepatocytes tended to be greater in the IP than the control group. Thus IP provides some functional protection against reversible ischemia but no protection during prolonged ischemia in pigs.
Altered endothelium-dependent relaxations in lambs with high pulmonary blood flow and pulmonary hypertension
Authors: Steinhorn Robin H. , Russell James A. , Lakshminrusimha Satyan , Gugino Sylvia F. , Black Stephen M. , Fineman Jeffrey R.
Published: December 2017

Congenital heart disease associated with increased pulmonary blood flow produces pulmonary hypertension. To characterize vascular alterations in the nitric oxide (NO)-cGMP cascade induced by increased pulmonary blood flow and pulmonary hypertension, 10 fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). When the lambs were 4–6 wk of age, we assessed responses of pulmonary arteries (PAs) and pulmonary veins (PVs) isolated from lungs of control and shunted lambs. PVs from control and shunted lambs relaxed similarly to exogenous NO ( S-nitrosyl-acetyl-penicillamine), to NO produced endogenously (zaprinast and A-23187), and to cGMP (atrial natriuretic peptide). In contrast, relaxations to A-23187 and zaprinast were blunted in PAs isolated from shunted lambs relative to controls. Inhibitors of NO synthase (NOS) and soluble guanylate cyclase constricted control but not shunt PAs, indicating reduced basal NOS activity in shunt PAs. Pretreatment of shunt PAs with the substratesl-arginine and sepiapterin, a precursor for tetrahydrobiopterin synthesis, did not augment A-23187 relaxations. However, pretreatment with superoxide dismutase and catalase significantly enhanced A-23187 relaxations in shunt PAs. We conclude that increased pulmonary blood flow induces an impairment of endothelium-dependent relaxation that is selective to PAs. The impaired relaxation may be mediated in part by excess superoxide production.
κ- but not δ-opioid receptors mediate effects of ischemic preconditioning on both infarct and arrhythmia in rats
Authors: Wang Guan-Ying , Wu Song , Pei Jian-Ming , Yu Xiao-Chun , Wong Tak-Ming
Published: December 2017

Two series of experiments were performed in the isolated perfused rat heart to determine the role of κ- and δ-opioid receptors (OR) in cardioprotection of ischemic preconditioning (IP). In the first series of experiments, it was found that IP with two cycles of 5-min regional ischemia followed by 5-min reperfusion each reduced infarct size induced by 30-min ischemia, and the ameliorating effect of IP on infarct was attenuated with blockade of either 5 × 10−6mol/l nor-binaltorphimine (nor-BNI), a selective κ-OR antagonist, or 5 × 10−6mol/l naltrindole (NTD), a selective δ-OR antagonist. The second series showed that U50,488H, a selective κ-OR agonist, ord-Ala2-d-leu5-enkephalin (DADLE), a selective δ-OR agonist, dose dependently reduced the infarct size induced by ischemia, which mimicked the effects of IP. The effect of 10−5mol/l U50,488H on infarct was significantly attenuated by blockade of protein kinase C (PKC) with specific PKC inhibitors, 5 × 10−6mol/l chelerythrine or 8 × 10−7mol/l calphostin C, as well as by blockade of ATP-sensitive K+(KATP) channels with blockers of the channel, 10−5mol/l glibenclamide or 10−4mol/l 5-hydroxydecanoate. IP also reduced arrhythmia induced by ischemia. Nor-BNI, but not NTD, attenuated, while U50,488H, but not DADLE, mimicked the antiarrhythmic action of IP. In conclusion, the present study has provided first evidence that κ-OR mediates the ameliorating effects of IP on infarct and arrhythmia induced by ischemia, whereas δ-OR mediates the effects only on infarct. Both PKC and KATPchannels mediate the effect of activation of κ-OR on infarct.
Enhanced systolic function of the right ventricle during respiratory distress syndrome in newborn lambs
Authors: De Vroomen Maartje , Steendijk Paul , Lopes Cardozo Robbert H. , Brouwers Hens H. A. , Van Bel Frank , Baan Jan
Published: December 2017

Respiratory distress syndrome (RDS) causes pulmonary hypertension. It is often suggested that this increased afterload for the right ventricle (RV) might lead to cardiac dysfunction. To examine this, we studied biventricular function in an experimental model. RDS was induced by lung lavages in seven newborn lambs. Five additional lambs served as controls. Cardiac function was quantified by indexes derived from end-systolic pressure-volume relations obtained by pressure-conductance catheters. After lung lavages, a twofold increase of mean pulmonary arterial pressure (from 15 to 34 mmHg) was obtained and lasted for the full 4-h study period. Stroke volume was maintained (5.2 ± 0.6 ml at baseline and 6.1 ± 1.4 ml at 4 h of RDS), while RV end-diastolic volume showed only a slight increase (from 6.5 ± 2.3 ml at baseline to 7.7 ± 1.3 ml at 4 h RDS). RV systolic function improved significantly, as indicated by a leftward shift and increased slope of the end-systolic pressure-volume relation. Left ventricular systolic function showed no changes. In control animals, pulmonary arterial pressure did not increase and right and left ventricular systolic function remained unaffected. In the face of increased RV afterload, the newborn heart is able to maintain cardiac output, primarily by improving systolic RV function through homeometric autoregulation.
Diurnal variations of the dominant cycle length of chronic atrial fibrillation
Authors: Meurling Carl J. , Waktare Johan E. P. , Holmqvist Fredrik , Hedman Antti , Camm A. John , Olsson S. Bertil , Malik Marek
Published: December 2017

High-resolution digital Holter recording was carried out in 21 patients (15 men, 64 ± 12 yr) with chronic atrial fibrillation. Dominating atrial cycle length (DACL) was derived by frequency domain analysis of QRST-reduced electrocardiograms. Daytime mean DACL was 150 ± 17 ms, and nighttime mean was 157 ± 22 ms ( P = 0.0002). Diurnal fluctuation in DACL differed among patients: it tended to be virtually absent in those with a short mean DACL, but in those with longer DACL the night-day difference was as much as 23 ms ( R = 0.72, P < 0.001, correlation of mean DACL to night-day difference). Mean DACL also correlated with ventricular cycle length ( R = 0.40, P < 0.001), particularly at night ( r = 0.49). The shorter cycle lengths found in this study during the day are consistent with sympathetic and/or other physiological modulation, but since increased vagal tone shortens atrial refractoriness in most models, parasympathetic influences are not likely to play a major role. Alternatively, atrial effective refractory period may not be the sole determinant of atrial cycle length during atrial fibrillation.