bluuebunny/crossref_metadata_2025 huggingface dataset:
Anesthetics alter relative contributions of NO and EDHF in rat cremaster muscle microcirculation
Authors: Loeb A. L. , Godeny I. , Longnecker D. E.
Published: December 2017

The contributions of the vasodilators nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) were investigated in the rat cremaster muscle microcirculation during halothane, isoflurane, or ketamine anesthesia. After inhibition of prostaglandin synthesis with indomethacin, changes in diameter of fourth-order arterioles to acetylcholine (ACh) or bradykinin (BK) were studied in the presence or absence of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase, and/or 20 mM K+, an inhibitor of EDHF action. L-NMMA inhibited ACh- and BK-induced vasodilation during isoflurane but not halothane or ketamine anesthesia. Superfusion of the muscle with buffer containing 20 mM K+ dilated arterioles. EDHF was responsible for most of the NO-independent response to ACh, because 20 mM K+ unmasked ACh-stimulated, NO-dependent relaxation during halothane or ketamine anesthesia. However, 20 mM K+ did not inhibit BK-induced vasodilation during halothane or ketamine anesthesia. Our data suggest that anesthetics can alter the balance between NO and EDHF vasodilation in the microcirculation and that NO-dependent mechanisms are enhanced and EDHF action inhibited during isoflurane anesthesia.
Phosphorylation potential, adenosine formation, and critical PO2 in stimulated rat cardiomyocytes
Authors: Stumpe T. , Schrader J.
Published: December 2017

This study investigated the relationship between O2 consumption (VO2) and energy status in isolated rat cardiomyocytes using a system in which O2 supply (PO2) was maintained constant. For this purpose, VO2, phosphocreatine, ATP, intracellular pH, and adenosine of quiescent and stimulated cardiomyocytes were measured while the ambient PO2 was clamped between 0.1 and 120 mmHg. In quiescent cardiomyocytes (VO2: 7.9 +/- 1.2 nmol.min-1.mg protein-1), the threshold below which respiration decreased (critical PO2) was 1.4 mmHg. Above this value, energy status remained constant; below 1 mmHg, both free ADP and adenosine increased. Stimulation increased VO2 threefold and shifted the critical PO2 to 10 mmHg. Above this value, free ADP and adenosine remained unchanged; between 10 and 5 mmHg. VO2 was reduced but this did not change free ADP or adenosine. These findings demonstrate that 1) under well-oxygenated conditions (PO2 > 10 mmHg), VO2 is not controlled by ADP; 2) similarly, the adenosine formation is independent of VO2; a PO2 < 5 mmHg is a prerequisite for enhanced adenosine formation; and 3) when O2 supply becomes limiting, ATP consumption is downregulated without measurable changes in energy status (hibernation).
Electrotonic modulation of electrical activity in rabbit atrioventricular node myocytes
Authors: Spitzer K. W. , Sato N. , Tanaka H. , Firek L. , Zaniboni M. , Giles W. R.
Published: December 2017

Electrotonic effects of electrically coupling atrioventricular (AV) nodal cells to each other and to real and passive models of atrial and ventricular cells were studied using a technique that does not require functional gap junctions. Membrane potential was measured in each cell using suction pipettes. Mutual entrainment of two spontaneously firing AV nodal cells was achieved with a junctional resistance (Rj) of 500 M omega, which corresponds to only 39 junctional channels, assuming a single-channel conductance of 50 pS. Coupling of AV nodal and atrial cells at Rj of 50 M omega caused hyperpolarization of the nodal cell, decreasing its action potential duration and either slowing or blocking diastolic depolarization in the AV node myocyte. Opposite changes occurred in the atrial action potential. When AV nodal and ventricular cells were coupled at Rj of 50 M omega, nodal diastolic potential was markedly hyperpolarized and diastolic depolarization was completely blocked with little change in ventricular diastolic potential. However, coupling did elicit marked changes in the action potential duration of both cells, with prolongation in the nodal cell and shortening in the ventricular cell. Nodal maximum upstroke velocity was increased by both atrial and ventricular coupling, as expected from the hyperpolarization that occurred. With an Rj of 50 M omega, spontaneous firing was blocked in all single AV nodal pacemaker cells during coupling to a real or passive model of an atrial or ventricular cell. These results demonstrate that action potential formation and waveform in a single AV nodal cell is significantly affected by electrical coupling to other myocytes.
Systemic hemodynamic determinants of blood pressure in women: age, physical activity, and hormone replacement
Authors: Hunt B. E. , Davy K. P. , Jones P. P. , DeSouza C. A. , Van Pelt R. E. , Tanaka H. , Seals D. R.
Published: December 2017

We tested the hypothesis that the age-related changes in systemic hemodynamic determinants of arterial blood pressure in healthy women are related to physical activity and hormone replacement status. We studied 66 healthy, normotensive premenopausal (21-35 yr) and postmenopausal (50-72 yr) sedentary and endurance-trained women under supine resting conditions. Mean blood pressure was 7 mmHg higher in sedentary post- compared with premenopausal women, which was associated with an 11-mmHg higher systolic blood pressure, a 25% lower stroke volume and cardiac output, and a 50% higher systemic vascular resistance (all P < 0.05). Absolute (ml) levels of total blood volume did not differ across age, but resting oxygen consumption was approximately 35% lower in the postmenopausal women (P < 0.05). The elevations in mean and systolic blood pressures with age were similar in endurance-trained runners, but, in contrast to the sedentary women, the elevations were not associated with significant age-related differences in cardiac output, stroke volume, or oxygen consumption, and only a modest (15%) increase in systemic vascular resistance (P = 0.06). Postmenopausal swimmers demonstrated the same systemic hemodynamic profile as that of postmenopausal runners, indicating a nonspecific influence of the endurance-trained state. Blood pressure and its systemic hemodynamic determinants did not differ in postmenopausal users compared with those of nonusers of hormone replacement therapy. Resting oxygen consumption was the strongest physiological correlate of cardiac output in the overall population (r = 0.65, P < 0.001). We conclude that 1) the increases in arterial blood pressure at rest with age in healthy normotensive women are not obviously related to habitual physical activity status; 2) the systemic hemodynamic determinants of the age-related elevations in blood pressure are fundamentally different in sedentary vs. active women, possibly due, in part, to an absence of decline in resting oxygen consumption in the latter; and 3) systemic hemodynamics at rest are not different in healthy normotensive postmenopausal users vs. nonusers of estrogen-based hormone replacement.
Distinct mechanisms for N-acetylcysteine inhibition of cytokine-induced E-selectin and VCAM-1 expression
Authors: Faruqi R. M. , Poptic E. J. , Faruqi T. R. , De La Motte C. , DiCorleto P. E.
Published: December 2017

We have examined the effects of N-acetyl-L-cysteine (NAC), a well-characterized, thiol-containing antioxidant, on agonist-induced monocytic cell adhesion to endothelial cells (EC). NAC inhibited interleukin-1 (IL-1 beta)-induced, but not basal, adhesion with 50% inhibition at approximately 20 mM. Monocytic cell adhesion to EC in response to tumor necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS), alpha-thrombin, or phorbol 12-myristate 13-acetate (PMA) was similarly inhibited by NAC. Unlike published studies with pyrrolidinedithiocarbamate, which specifically inhibited vascular cell adhesion molecule 1 (VCAM-1), NAC inhibited IL-1 beta-induced mRNA and cell surface expression of both E-selectin and VCAM-1. NAC had no effect on the half-life of E-selectin or VCAM-1 mRNA. Although NAC reduced nuclear factor-kappa B (NF-kappa B) activation in EC as measured by gel-shift assays using an oligonucleotide probe corresponding to the consensus NF-kappa B binding sites of the VCAM-1 gene (VCAM-NF-kappa B), the antioxidant had no appreciable effect when an oligomer corresponding to the consensus NF-kappa B binding site of the E-selectin gene (E-selectin-NF-kappa B) was used. Because NF-kappa B has been reported to be redox sensitive, we studied the effects of NAC on the EC redox environment. NAC caused an expected dramatic increase in the reduced glutathione (GSH) levels in EC. In vitro studies demonstrated that whereas the binding affinity of NF-kappa B to the VCAM-NF-kappa B oligomer peaked at a GSH-to-oxidized glutathione (GSSG) ratio of approximately 200 and decreased at higher ratios, the binding to the E-selectin-NF-kappa B oligomer appeared relatively unaffected even at ratios > 400, i.e., those achieved in EC treated with 40 mM NAC. These results suggest that NF-kappa B binding to its consensus sequences in the VCAM-1 and E-selectin gene exhibits marked differences in redox sensitivity, allowing for differential gene expression regulated by the same transcription factor. Our data also demonstrate that NAC increases the GSH-to-GSSG ratio within the EC suggesting one possible mechanism through which this antioxidant inhibits agonist-induced monocyte adhesion to EC.
Delayed preconditioning of cultured adult rat cardiac myocytes: role of 70- and 90-kDa heat stress proteins
Authors: Nayeem M. A. , Hess M. L. , Qian Y. Z. , Loesser K. E. , Kukreja R. C.
Published: December 2017

We investigated the protective effect of heat stress and metabolic preconditioning in cultured adult rat cardiac myocytes and correlated this effect with induction of heat shock proteins (HSP). Myocytes were preconditioned with sublethal heat shock or metabolic preconditioning for 30 min. Twenty hours later, preconditioned myocytes were subjected to lethal heat shock (46 degrees C for 2 h) or ischemia by incubation in ischemic buffer for 2 h. Cellular injury index was reduced from 69 +/- 4.0% in lethally heat-shocked cells to 27.0 +/- 1.6% with heat shock preconditioning (mean +/- SE; P < 0.01) and 19.0 +/- 3.0% with metabolic preconditioning (P < 0.01). Cellular injury index was 81.0 +/- 1.0% in ischemic myocytes and was reduced to 25.9 +/- 2.7 and 21.4 +/- 2.6% in heat shock- and metabolic-preconditioned myocytes, respectively (P < 0.01). A significant cross-tolerance of myocytes against lethal injury was observed with the two preconditioning methods. Western blot analysis revealed 3.3- and 2.5-fold increases in HSP 90 and 500- and 15-fold increases in HSP 70 with heat shock and metabolic preconditioning, respectively. HSP 27 expression remained unaltered relative to control cells. We conclude that heat shock and metabolic preconditioning induce delayed tolerance against lethal injuries in adult cardiac myocytes with elevated levels of HSP 70 and HSP 90.
Response of resistance arteries to reduced PO2 and vasodilators during hypertension and elevated salt intake
Authors: Liu Y. , Fredricks K. T. , Roman R. J. , Lombard J. H.
Published: December 2017

This study assessed vasodilator responses in skeletal muscle resistance arteries (100-250 microns) from rats with chronic (4-8 wk) reduced renal mass (RRM) hypertension and normotensive sham-operated controls on a high (4% NaCl; HSSHAM)- or low (0.4% NaCl; LSSHAM)-salt diet. Arteries from RRM hypertensive rats [normal and high-salt diet (HSRRM)] and a separate group of spontaneously hypertensive rats exhibited an impaired dilation in response to reduced PO2 compared with those of their normotensive controls. Prostacyclin release, assessed by radio-immunoassay for 6-ketoprostaglandin F1 alpha, increased significantly in response to reduced PO2, but was unaffected by hypertension or salt intake. Dilator responses to acetylcholine and the prostacyclin analog iloprost were significantly reduced in both HSRRM and HSSHAM compared with LSSHAM rats. Dilation in response to direct activation of adenylate cyclase with forskolin or guanylate cyclase with the nitric oxide donor sodium nitroprusside was not significantly different in HSRRM, HSSHAM, and LSSHAM rats. These results indicate that hypoxic dilation is impaired in skeletal muscle resistance arteries of hypertensive rats and that chronic high-salt diet alone leads to impaired vasodilator responses in resistance arteries of normotensive animals, possibly via abnormalities in membrane function or G protein signaling rather than impaired second-messenger function.
Endothelium-dependent regulation of cerebrovascular tone by extracellular and intracellular ATP
Authors: Janigro D. , Nguyen T. S. , Meno J. , West G. A. , Winn H. R.
Published: December 2017

ATP receptors and ATP-sensitive potassium channels (KATP) are expressed in vascular smooth muscle (VSM) and endothelial cells (EC). In isolated penetrating vessels, ATP caused a dilatation when applied intraluminally but not extraluminally. The actions of ATP were blocked by the nitric oxide (NO) synthesis inhibitor N omega-nitro-L-arginine (0.1 mM) but were only reduced by N-monomethyl-L-arginine (0.1 mM); responses to intraluminal ATP were also prevented by thapsigargin. The KATP opener (KCO) nicorandil (1 microM) caused an NO-independent vasodilatation when applied extraluminally and an NO-dependent response when applied intraluminally. Both responses were blocked by glibenclamide. EC-mediated responses to nicroandil were prevented by blockade of guanylate cyclase by LY-83583 (10 microM). The effects of nicorandil were mimicked by pinacidil (1-10 microM). Exposure of the endothelium to 500 microM cyanide and 0 mM glucose ("in vitro ischemia") caused a vasodilatation that was reduced by exposure to glibenclamide (5 microM). Blockade of NO synthase produced similar effects, suggesting that the ischemic dilation is mediated by KATP and NO. Our results suggest that both VSM and EC mediate the vascular responses induced by KCOs, whereas the dilatation induced by intraluminal ATP is mediated by the endothelium. The endothelium-dependent component of the in vitro ischemic vasodilatation is mediated by opening of endothelial KATP and subsequent release of NO.
Left ventricular spherical dilation and regional contractile dysfunction in dogs with heart failure
Authors: Suzuki M. , Cheng C. P. , Ohte N. , Little W. C.
Published: December 2017

Left ventricular (LV) short- and long-axis contractile function and LV structural changes were serially measured in eight instrumented dogs during the development of congestive heart failure (CHF) induced by rapid right ventricular (RV) pacing. After 10 days of pacing, LV end-diastolic volume (VED) had not increased; however, the slope of LV end-systolic pressure-volume relation had decreased from 7.4 +/- 2.6 to 4.9 +/- 1.1 mmHg/ml (P < 0.05), and the slope of LV stroke work-VED relation had fallen from 78.4 +/- 9.1 to 64.2 +/- 7.2 mmHg (P < 0.05). The slopes of end-systolic pressure-dimension relation and the stroke work area-end-diastolic dimension relation in the short axes (i.e., anteroposterior and septal-lateral) had decreased by 30% (P < 0.05), whereas the slopes of the long-axis (i.e., apical-basal) relations were unchanged (not significant). After 20 days of pacing, VED had significantly increased by 14% due to selective dilation of the short axes by 7%, and LV global contractility had further declined with a 40% contractile depression in the short axes and a 25% contractile depression in the long axis. After 30 days, the long-axis dimension at end diastole was also significantly increased with a further increase in the short-axis dimensions. In contrast to the spherical dilation occurring during CHF, acute volume loading of normal animals produced symmetrical LV dilation. These observations suggest that heterogeneous contractile depression initiates the spherical end-diastolic chamber dilation in pacing-induced CHF.
Ins(1,4,5)P3 and arrhythmogenic responses during myocardial reperfusion: evidence for receptor specificity
Authors: Jacobsen A. N. , Du X. J. , Dart A. M. , Woodcock E. A.
Published: December 2017

Reperfusion of ischemic rat hearts initiates the generation of inositol(1,4,5)trisphosphate [Ins(1,4,5)P3] and arrhythmias, provided that either norepinephrine or thrombin is present. In the current study, effects on endothelin-1 (ET-1) responses were investigated. Reperfusion of catecholamine-depleted, [3H]inositol-labeled hearts in the presence of ET-1 caused an increase in [3H]inositol phosphates (7,073 +/- 1,004 to 17,300 +/- 206 counts.min-1.g tissue-1, means +/- SE, n = 4, P < 0.01), which was quantitatively greater than the release observed under normoxic conditions, but there was no increase in [3H]Ins(1,4,5)P3. Gentamicin (150 microM) inhibited inositol phosphate responses in the presence of either norepinephrine or thrombin but did not inhibit the response to ET-1, providing additional evidence that the inositol phosphate response to ET-1 does not involve formation of Ins(1,4,5)P3, even under reperfusion conditions. In contrast to norepinephrine and thrombin, ET-1 did not initiate reperfusion arrhythmias (4.4% ventricular fibrillation compared with 0% ventricular fibrillation in catecholamine-depleted controls). The data provide strong evidence that the effect of ischemia-reperfusion on inositol phosphate responses is specific for particular receptor types and eliminates G proteins, phospholipase C enzymes, and substrate availability as the primary factors responsible for Ins(1,4,5)P3 generation under reperfusion conditions.
Role of sympathetic nervous system in cardiovascular effects of centrally administered endothelin-1 in rats
Authors: Gulati A. , Rebello S. , Kumar A.
Published: December 2017

Centrally administered endothelin-1 (ET-1) produces a biphasic response, an initial increase followed by a decrease in blood pressure (BP). The pressor effect is due to stimulation of the sympathetic nervous system and/or release of vasopressin. The mechanism responsible for the depressor effect after central administration of ET-1 is still not known. Systemic and regional circulatory effects of intracerebroventricular (i.c.v.) administration of ET-1 (100 ng) were determined in anesthetized rats, using a radioactive microsphere technique. BP, cardiac output, and stroke volume were significantly decreased 30, 60, and 120 min after central administration of ET-1. Heart rate and total peripheral resistance were not altered. ET-1 produced a reduction in blood flow to the brain (83%), heart (62%), kidneys (53%), gastrointestinal tract (43%), portal system (46%), and musculoskeletal system (55%). To determine the role of the central nervous system in cardiovascular effects of centrally administered ET-1, experiments were performed in cervical-sectioned rats. The changes in systemic and regional blood circulation induced by centrally administered ET-1 in normal rats were not observed in cervical-sectioned rats. Pretreatment with a specific antagonist of ETA receptors, BQ-123 (10 micrograms i.c.v.), antagonized systemic and regional circulatory effects of ET-1. Centrally administered clonidine (1 microgram i.c.v.) produced hypotension and bradycardia, known to be mediated through the sympathetic nervous system. Pretreatment with an ETA receptor antagonist, BMS-182874 (50 micrograms/kg iv), blocked clonidine-induced hypotension and bradycardia. We conclude that centrally administered ET-1 stimulates ETA receptors to produce systemic and regional circulatory changes mediated by the sympathetic nervous system.
Influence of stimulation frequency on [Na+]i and contractile function in Langendorff-perfused rat heart
Authors: Maier L. S. , Pieske B. , Allen D. G.
Published: December 2017

To study the relationship between stimulation frequency and intracellular Na+ concentration ([Na+]i), Langendorff-perfused rat hearts were loaded with the Na(+)-sensitive dye sodium-binding benzofuran isophthalate (SBFI). An intracellular calibration procedure allowed SBFI fluorescence to be transformed into [Na+]i. Compartmentation of SBFI was evaluated by permeabilizing sarcolemmal membranes with saponin and subcellular compartments with Triton X-100. Most of the indicator was located in the myoplasm (69%). When stimulation frequency was increased from 0 to 6 Hz, [Na+]i increased from 3.0 to 7.9 mM, whereas pressure amplitude (PA) declined to 49% of the maximum recorded at 2 Hz. Blocking sarcoplasmic reticulum (SR) Ca2+ uptake with 2,5-di(tert-butyl)-1,4-benzohydroquinone (TBQ; 10 microM) at 2 Hz increased [Na+]i from 4.9 to 8.4 mM and decreased PA by 70%. Raising stimulation frequency then resulted in a further increase in [Na+]i and decline in PA. In conclusion, these data indicate that the rat heart is characterized by a negative pressure-frequency relationship associated with increasing [Na+]i at higher heart rates. After inhibition of SR Ca2+ uptake, [Na+]i further increases, whereas PA declines with increasing stimulus frequency. It is suggested that part of the rise of [Na+]i with stimulus frequency and TBQ may be associated with increased Ca2+ extrusion and Na+ influx on the Na+/Ca2+ exchange system.
Force-frequency effect is a powerful determinant of myocardial contractility in the mouse
Authors: Palakodeti V. , Oh S. , Oh B. H. , Mao L. , Hongo M. , Peterson K. L. , Ross J.
Published: December 2017

The effects of heart rate (HR) on myocardial contractility in the mouse heart in situ were first investigated in open-chest mice (n = 7) by left ventricular (LV) catheter-tip micromanometry. HR was first slowed with a sinus node inhibitor (zatebradine), and atrial pacing to progressively increase the HR caused a positive inotropic response (assessed by maximum positive first derivative of LV pressure, LV dP/dtmax) up to a HR of 282 beats/min with the onset of a descending limb of the force-frequency relation (FFR) at 332 beats/min. beta-Adrenergic receptor stimulation (dobutamine) shifted upward and significantly steepened the positive FFR and increased HR at the onset of the descending limb to 402 beats/min. HR and LV dP/dtmax were then studied in closed-chest mice without pacing during recovery from anesthesia (n = 7), and during rest and intermittent physical activity the FFR was linear and positive up to 600 beats/min. HR was then progressively slowed with zatebradine, and the points at rest and during activity fell on the same linear relation. Thus we conclude the following: 1) in the open-chest anesthetized mouse, a positive FFR was amplified by beta-adrenergic receptor stimulation, and 20 in the mouse recovering from anesthesia the sinus node rate remained a critical determinant of myocardial contractility, without a descending limb of the FFR.
Role of ATP-sensitive potassium channels in brain stem circulation during hypotension
Authors: Toyoda K. , Fujii K. , Ibayashi S. , Kitazono T. , Nagao T. , Fujishima M.
Published: December 2017

The basilar artery and its branch arterioles dilate actively in response to a marked decrease in blood pressure and maintain cerebral blood flow (CBF) to the brain stem. We tested the hypothesis that ATP-sensitive potassium (KATP) channels play a role in the autoregulatory responses of the brain stem circulation in vivo. In anesthetized Sprague-Dawley rats, local CBF to the brain stem was determined with laser-Doppler flowmetry, and diameters of the basilar artery and branch arterioles were measured through a cranial window during stepwise hemorrhagic hypotension. During topical application of 10(-6) and 10(-5) mol/l of glibenclamide, a selective KATP-channel blocker, the lower limit of CBF autoregulation shifted upward to 60-75 from 30-45 mmHg in the vehicle group. Glibenclamide significantly impaired the dilator response of small arterioles (baseline diameter 45 +/- 2 microns) throughout hypotension (P < 0.03) but did not impair the dilatation of the basilar artery (247 +/- 3 microns) or large arterioles (99 +/- 4 microns). Thus KATP channels appear to play an important role in the regulation of CBF to the the brain stem during hypotension by mediating the compensatory dilatation of small arterioles. In contrast, these channels may not be a major regulator of the vascular tone of larger arteries during hypotension.
Downregulation of cyclin-dependent kinase inhibitors p21 and p27 in pressure-overload hypertrophy
Authors: Li J. M. , Brooks G.
Published: December 2017

We postulated that the cyclin-dependent kinase inhibitors p21 and p27 could regulate the alterations in growth potential of cardiomyocytes during left ventricular hypertrophy (LVH). LVH was induced in adult rat hearts by aortic constriction (AC) and was monitored at days 0, 1, 3, 7, 14, 21, and 42 postoperation. Relative to sham-operated controls (SH), left ventricle (LV) weight-to-body weight ratio in AC increased progressively with time without significant differences in body weight or right ventricle weight-to-body weight ratio. Atrial natriuretic factor mRNA increased significantly in AC to 287% at day 42 compared with SH (P < 0.05), whereas p21 and p27 mRNA expression in AC rats decreased significantly by 58% (P < 0.03) and 40% (P < 0.05) at day 7, respectively. p21 and p27 protein expression decreased significantly from days 3 to 21 in AC versus SH, concomitant with LV adaptive growth. Immunocytochemistry showed p21 and p27 expression in cardiomyocyte nuclei. Thus downregulation of p21 and p27 may modulate the adaptive growth of cardiomyocytes during pressure overload-induced LVH.
Ca(2+)-dependent outward currents in myocytes from epicardial border zone of 5-day infarcted canine heart
Authors: Aggarwal R. , Pu J. , Boyden P. A.
Published: December 2017

Myocytes from the epicardial border zone (EBZ) of the 5-day infarcted canine heart (IZ) have abnormal transmembrane action potentials, reduced L-type Ca2+ currents (ICa,L) and altered intracellular Ca2+ (Cai) transients compared with those of normal epicardial myocytes (NZ). We hypothesized that altered Cai cycling might be reflected in differences in Cai-dependent outward currents (Ito2). We recorded Ito2 in NZ and IZ using whole cell patch-clamp techniques. Ito2 was defined as the amplitude of the 4-aminopyridine-resistant transient outward current that was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) or DIDS+ ryanodine (2 microM). Ito2 were present in both NZ and IZ, but peak density was significantly reduced in IZ, particularly at positive plateau voltages. Time course of decay of Ito2 was biexponential and similar in NZ and IZ. A given peak ICa,L was usually associated with a smaller peak Ito2 in IZ. These differences were exaggerated when Ito2 and Cai transients were determined in rapidly paced cells. In summary, myocytes surviving in the EBZ of the infarcted heart have Ito2, yet they are reduced in density and can vary, particularly at fast pacing rates.
Regional differentiation in the rat aorta for a novel signaling pathway: leucine to glutamate
Authors: Schachter D. , Sang J. C.
Published: December 2017

Rat aortic endothelium is differentiated regionally for regulating guanosine 3',5'-cyclic monophosphate (cGMP) levels in underlying smooth muscle by signaling via nitric oxide and prostaglandin H2. Highest activity is just distal to the aortic arch and diminishes peripherally. The same differentiation pattern is reported here for a third and novel signal pathway: endothelial conversion of L-leucine to L-glutamate. Sequential segments of rat aorta incubated in vitro convert L-[U-14C]leucine to a major 14C metabolite identified as L-glutamate. Net synthesis of glutamate is greatest in aortic segments of the "windkessel" region; significant quantities are also observed in the pancreas, testis, and lung but very little in 10 additional tissues. Endothelial cells cultured from mouse brain, human umbilical vein, or bovine aorta and human peripheral blood macrophages also form [14C]glutamate. When aortic segments are denuded of endothelium, treatment with L-glutamate in the presence of 3-isobutyl-1-methylxanthine significantly increases the cGMP content. A number of leucine derivatives inhibit the leucine-to-glutamate conversion and decrease the cGMP content in aortic segments in vitro.
Hemodynamic effects of L- and D-S-nitroso-beta,beta-dimethylcysteine in rats
Authors: Travis M. D. , Davisson R. L. , Bates J. N. , Lewis S. J.
Published: December 2017

This study examined whether S-nitroso-beta,beta-dimethylcysteine (S-nitrosopenicillamine; SNPEN) may activate stereoselective S-nitrosothiol receptors within the vasculature. We examined 1) the hemodynamic effects produced by the L- and D-isomers of SNPEN (12.5-400 nmol/kg iv), the L- and D-isomers of the parent thiols [L- and D-penicillamine (PEN); 12.5-400 nmol/kg iv], and the nitric oxide (NO) donor sodium nitroprusside (SNP; 1-10 micrograms/kg iv) in conscious rats; 2) the hemodynamic effects produced by these compounds in urethan-anesthetized rats; and 3) the relative decomposition of L- and D-SNPEN to NO on addition to rat blood or cultured porcine aortic smooth muscle (PASM) cells. We found that 1) L-SNPEN was a more potent hypotensive and vasodilator agent within the mesenteric bed and within sympathetically intact and sympathetically denervated hindlimb beds of conscious rats than was D-SNPEN; 2) the hypotension and vasodilation produced by L-SNPEN was similar in conscious and anesthetized rats, whereas the effects of D-SNPEN and SNP were augmented by urethan-anesthesia; 3) L- and D-PEN did not affect hemodynamic parameters in conscious or anesthetized rats; and 4) L- and D-SNPEN decomposed equally to NO on addition to rat blood or PASM cells. These results suggest that the vasodilator effects of SNPEN involve the interaction of this S-nitrosothiol with stereoselective recognition sites within the vasculature and that urethan alters the mechanisms by which L- and D-SNPEN relax vascular smooth muscle.
Finite-element simulation of blood perfusion in muscle tissue during compression and sustained contraction
Authors: Vankan W. J. , Huyghe J. M. , Slaaf D. W. , van Donkelaar C. C. , Drost M. R. , Janssen J. D. , Huson A.
Published: December 2017

Mechanical interaction between tissue stress and blood perfusion in skeletal muscles plays an important role in blood flow impediment during sustained contraction. The exact mechanism of this interaction is not clear, and experimental investigation of this mechanism is difficult. We developed a finite-element model of the mechanical behavior of blood-perfused muscle tissue, which accounts for mechanical blood-tissue interaction in maximally vasodilated vasculature. Verification of the model was performed by comparing finite-element results of blood pressure and flow with experimental measurements in a muscle that is subject to well-controlled mechanical loading conditions. In addition, we performed simulations of blood perfusion during tetanic, isometric contraction and maximal vasodilation in a simplified, two-dimensional finite-element model of a rat calf muscle. A vascular waterfall in the venous compartment was identified as the main cause for blood flow impediment both in the experiment and in the finite-element simulations. The validated finite-element model offers possibilities for detailed analysis of blood perfusion in three-dimensional muscle models under complicated loading conditions.
Effect of vasoactive drugs on carotid diameter in humans
Authors: Bonyhay Istvan , Jokkel Gabor , Karlocai Kristof , Reneman Robert , Kollai Mark
Published: December 2017

We studied whether vasoactive drugs used to determine baroreflex sensitivity influence baroreceptor firing by affecting carotid sinus smooth muscle or simply by stretching the sinus wall through changes in pressure. In six young healthy subjects, the diameter of the carotid artery and its change with arterial pulse were measured with ultrasonography. Blood pressure was measured by Finapres. Phenylephrine and nitroglycerin doses were injected intravenously to raise and lower pressure by ∼15–25 mmHg. Carotid dimensions increased in all subjects during the phenylephrine-induced rise and decreased during the nitroglycerin-induced fall in pressure. Diastolic diameter changed more than systolic diameter; changes were significantly different from the control value (assessed by single-factor analysis of variance and Scheffé’s post hoc test). The systolic pressure-diameter relationship appeared to be nonlinear, with a steeper slope above than below baseline, and contributed significantly to the nonlinearity of the R-R interval-systolic pressure relationship. It is concluded that during drug-induced changes in blood pressure, baroreceptor activity in humans is influenced more by passive stretch than by local smooth muscle contraction.
Priming effect of adenosine on KATP currents in intact ventricular myocytes: implications for preconditioning
Authors: Liu Yongge , Gao Wei Dong , O’Rourke Brian , Marban Eduardo
Published: December 2017

Activation of protein kinase C (PKC) by the phorbol ester phorbol 12-myristate 13-acetate (PMA) has been shown to shorten the time to turn on ATP-sensitive potassium currents ( I K,ATP) during metabolic inhibition (MI) but only when adenosine (Ado) is included. In the present study we tested whether pretreatment with Ado could mimic the effect of PMA in isolated rabbit ventricular myocytes. When I K,ATP was measured by conventional whole cell clamp, pretreatment with 100 μM Ado did not alter the time to I K,ATPactivation: 13.5 ± 2.1 vs. 12.4 ± 1.9 min with Ado during MI. We repeated the experiment using the perforated patch technique. Consistent with the previous results in conventional whole cell patch recordings, the time to turn on I K,ATP during MI (with Ado included) was shortened from 27.1 ± 2.2 to 12.6 ± 2.4 min ( P < 0.01) when cells were pretreated with PMA and Ado was included during MI. In contrast to conventional whole cell recordings, Ado pretreatment also abbreviated the time for I K,ATP activation during MI (with Ado included) to 16.4 ± 1.8 min. This effect was partially eliminated by simultaneous administration of an Ado receptor blocker or a PKC inhibitor during Ado pretreatment, suggesting that pretreatment with Ado stimulates PKC by activating Ado receptors. Our results demonstrate that Ado can prime I K,ATP during subsequent MI in the presence of Ado. This priming effect appears to be mediated by PKC upregulation of the channel. These results support the notion that Ado plays a dual role to initiate and to mediate ischemic preconditioning and links the roles of Ado receptors, PKC, and I K,ATP in ischemic preconditioning.
Stimulation of left stellate ganglion prolongs Q-T interval in patients with palmar hyperhidrosis
Authors: Wong Cheuk-Wah
Published: December 2017

With the advent of transthoracic video-assisted endoscopic electrocautery of the second and the third sympathetic ganglia for the treatment of palmar hyperhidrosis, it is possible to approach the stellate ganglia with ease. To see whether stimulation of stellate ganglia in humans is similar to the case in dogs, we stimulated the sympathetic ganglia in 18 palmar hyperhidrosis patients with a coagulation power of 5 W at a frequency of three times every 2 s. We found that left stellate stimulation prolongs the Q-T interval and increases the heart rate, whereas right stellate stimulation affects the Q-T interval and heart rate insignificantly, just like the case in dogs in which the left stellate ganglion predominates the right one in determining the Q-T interval. Left stellate stimulation after destruction of the left second and third ganglia also prolongs the Q-T interval, suggesting that the left stellate ganglion is more important in determining the Q-T interval.
Angiotensin II formation from ACE and chymase in human and animal hearts: methods and species considerations
Authors: Balcells Eduardo , Meng Qing C. , Johnson Walter H. , Oparil Suzanne , Dell’Italia Louis J.
Published: December 2017

The current study examined the contributions of angiotensin-converting enzyme (ACE) vs. chymase to angiotensin II (ANG II) generation in membrane preparations from left ventricles of humans, dogs, rabbits, and rats and from total heart of mice. ACE and chymase activity were measured in membrane preparations extracted with low or high detergent (LD and HD, respectively) concentrations. We hypothesized that ACE, which is membrane bound in vivo, would be preferentially localized to the HD preparation, whereas chymase, which is localized to the cytoplasm and cardiac interstitium, would be localized to the LD preparation. In human heart, ACE activity was 16-fold higher in the HD than in the LD preparation, whereas chymase activity was 15-fold higher in the LD than in the HD preparation. Total ANG II formation was greater in human heart [15.8 ± 3.4 (SE) μmol ANG II ⋅ g−1⋅ min−1] than in dog, rat, rabbit, and mouse hearts (3.90 ± 0.35, 0.41 ± 0.02, 0.61 ± 0.07, and 1.16 ± 0.08 μmol ANG II ⋅ g−1⋅ min−1, respectively, P < 0.05, by analysis of variance). ANG II formation from ACE was higher in mouse heart (1.09 ± 0.05 μmol ANG II ⋅ g−1⋅ min−1, P < 0.001) than in rabbit, human, dog, and rat hearts (0.55 ± 0.06, 0.34 ± 0.01, 0.32 ± 0.06, and 0.31 ± 0.02 μmol ANG II ⋅ g−1⋅ min−1, respectively). In contrast, chymase activity was higher in human heart (15.3 ± 3.4 μmol ANG II ⋅ g−1⋅ min−1) than in dog, rat, rabbit, and mouse hearts (3.59 ± 0.29, 0.10 ± 0.01, 0.06 ± 0.01, and 0.07 ± 0.01 μmol ANG II ⋅ g−1⋅ min−1, respectively). Our results demonstrate important species differences in the pathways of intracardiac ANG II generation. Chymase predominated over ACE activity in human heart, accounting for extremely high total ANG II formation in human heart compared with dog, rat, rabbit, and mouse hearts.
Dose-dependent effect of ANG II-receptor antagonist on myocyte remodeling in rat cardiac hypertrophy
Authors: Obayashi Masakazu , Yano Masafumi , Kohno Michihiro , Kobayashi Shigeki , Tanigawa Taketo , Hironaka Katsumi , Ryouke Tsutomu , Matsuzaki Masunori
Published: December 2017

The goal of this study was to examine the effect of an angiotensin II type 1 (AT1)-receptor antagonist (TCV-116) on left ventricular (LV) geometry and function during the development of pressure-overload LV hypertrophy. A low (LD; 0.3 mg ⋅ kg−1⋅ day−1) or a high (HD; 3.0 mg ⋅ kg−1⋅ day−1) dose of TCV-116 was administered to abdominal aortic-banded rats over 4 wk, and hemodynamics and morphology were then evaluated. In both LD and HD groups, peak LV pressures were decreased to a similar extent compared with the vehicle-treated group but stayed at higher levels than in the sham-operated group. In the LD group, both end-diastolic wall thickness (3.08 ± 0.14 mm) and myocyte width (13.3 ± 0.1 μm) decreased compared with those in the vehicle-treated group (3.67 ± 0.19 mm and 15.3 ± 0.1 μm, respectively; both P < 0.05). In the HD group, myocyte length was further decreased (HD: 82.6 ± 2.6, LD: 94.1 ± 2.9 μm; P < 0.05) in association with a reduction in LV midwall radius (HD: 3.36 ± 0.12, LD: 3.60 ± 0.14 mm; P < 0.05) and peak midwall fiber stress (HD: 69 ± 8, LD: 83 ± 10 × 103dyn/cm2; P < 0.05). There was no significant difference in cardiac output among all groups. The AT1-receptor antagonist TCV-116 induced an inhibition of the development of pressure-overload hypertrophy. Morphologically, not only the width but also the length of myocytes was attenuated with TCV-116, leading to a reduction of midwall radius and hence wall stress, which in turn may contribute to a preservation of cardiac output.
Ischemic preconditioning triggers phospholipase D signaling in rat heart
Authors: Tosaki Arpad , Maulik Nilanjana , Cordis Gerald , Trifan Ovidiu C. , Popescu Laurentiu M. , Das Dipak K.
Published: December 2017

Recent studies have indicated that repeated brief episodes of ischemia and reperfusion render the myocardium more tolerant to subsequent lethal ischemic injury. In view of the previous observations that ischemia-reperfusion potentiates phospholipase D signaling and that such signaling is beneficial for the heart, we investigated whether a similar phospholipase D signaling is responsible for the beneficial effects associated with repeated ischemia and reperfusion. Using an isolated perfused working rat heart model, we demonstrated that four brief episodes of 5 min of ischemia and 10 min of reperfusion reduced the incidence of ventricular arrhythmias, enhanced the postischemic ventricular performance, and decreased the release of creatine kinase from the reperfused heart, with simultaneous activation of phospholipase D generating the second messengers diacylglycerol and phosphatidic acid and leading to the translocation and activation of protein kinase C. The specific antiphospholipase D antibody blocked the activation of phospholipase D and attenuated the generation of diacylglycerol and phosphatidic acid and activation of protein kinase C. In concert, phospholipase D inhibition increased the incidence of ventricular arrhythmias, blocked the beneficial effects of preconditioning on the ventricular performance, and increased the amount of creatine kinase release from the coronary effluent. The results of this study indicate that repeated brief episodes of ischemia and reperfusion exert beneficial effects on the intact rat heart by triggering the activation of a phospholipase D signaling mechanism.
Diabetes with and without ketoacidosis on right atrial pacemaker rate and autonomic responsiveness
Authors: Hicks Kristine K. , Seifen Ernst , Stimers Joseph R. , Kennedy Richard H.
Published: December 2017

Experiments were designed to determine whether insulin-dependent diabetes mellitus (IDDM) alters direct chronotropic effects of adrenergic and cholinergic agonists and whether the observed changes are associated with hyperglycemia or combined hyperglycemia and ketoacidosis. Diabetes was induced by intravenous administration of 45, 50, or 65 mg/kg streptozotocin (STZ). Rats treated with 65 mg/kg STZ had higher levels of blood glucose and ketones compared with the levels of the other groups. Right atria were isolated 12 wk after administration of STZ and bathed in Krebs-Henseleit solution. Basal spontaneous pacemaker rate was diminished in preparations isolated from diabetic rats. The maximum pacemaker rate observed during exposure to isoproterenol or norepinephrine was also depressed in preparations from diabetic animals; however, the increase in rate and half-maximal effective concentration values for each agent were not affected. The sensitivity to the negative chronotropic action of acetylcholine was enhanced by IDDM, whereas the response to carbachol (a cholinergic agonist not readily metabolized by acetylcholinesterase) was not changed. No significant differences were observed when we compared preparations isolated from diabetic animals with and without ketoacidosis. In summary, these data suggest 1) that IDDM is associated with a diminished basal spontaneous pacemaker without changes in the responsiveness to adrenergic and cholinergic receptor activation and 2) that ketoacidosis does not play a role in the observed alterations.
Role of AVP in pressor responses during activation of central TxA2/PGH2receptors
Authors: Wilcox Christopher S. , Gao Hubin , Verbalis Joseph G. , Welch William J.
Published: December 2017

Administration of thromboxane A2/prostaglandin H2(TxA2/PGH2)-receptor agonist U-46619 (2.86 nmol/kg iv) to conscious rats increased mean arterial pressure (MAP) by 17 ± 2 mmHg ( n = 6; P < 0.001) and plasma arginine vasopressin (AVP) by 3.5 ± 1.1 IU/ml ( n = 6; P < 0.001). Ifetroban (TxA2/PGH2antagonist; intracerebroventricularly) prevented both responses. Intracerebroventricular U-46619 increased MAP in Long-Evans rats ( n = 6) more than in AVP-deficient Brattleboro rats. AVP V1-receptor antagonist d(CH2)5Tyr(Me)AVP (3 μg/kg iv) blocked 67 ± 5% and 69 ± 7% of pressor response to intravenous AVP and intracerebroventricular U-46619, respectively. AVP (10 ng/kg iv) increased AVP by 4.7 ± 0.5 pg/ml, comparable to the increase of 3.5 ± 1.2 pg/ml with intracerebroventricular U-46619 (2.86 nmol/kg), but the rise in MAP was only one-half as great (+8 ± 3 mmHg for AVP vs. +17 ± 2 mmHg for U-46619; P < 0.05). In conclusion, U-46619 raises blood pressure and releases AVP by activating brain receptors. AVP explains approximately one-half of the pressor response.
Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo
Authors: Portman Michael A. , Xiao Yun , Song Ying , Ning Xue-Han
Published: December 2017

Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MV˙o2) were induced by epinephrine infusion in newborn (0–32 h, n = 6) and mature sheep (30–32 days, n = 6), and high-energy phosphates were monitored with31P nuclear magnetic resonance. Western blot analyses for the ANT1and the β-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional ( n = 9 total per group) as well as in fetal hearts (130–132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the31P spectra data revealed that the ADP-MV˙o2relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in β-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and β-F1-ATPase increased ∼2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.
Baroreflex sensitivity and heart rate variability in conscious rats with myocardial infarction
Authors: Krüger Carsten , Kalenka Armin , Haunstetter Armin , Schweizer Mark , Maier Christoph , Rühle Ulrike , Ehmke Heimo , Kübler Wolfgang , Haass Markus
Published: December 2017

The baroreflex sensitivity (BRS) and the heart rate variability (HRV) were studied in conscious rats after myocardial infarction (MI; induced by coronary artery ligation) and after sham operation (SH). BRS was determined by linear regression of R-R interval vs. arterial pressure changes induced by nitroprusside or methoxamine (intravenous bolus). HRV was calculated from 3-min electrocardiogram recordings. Left ventricular end-diastolic pressure and plasma atrial natriuretic peptide were increased after MI; plasma norepinephrine and basal heart rate (HR) remained unchanged. At 3 and 28 days after MI, BRS was reduced as indicated by decreased reflex bradycardia (RB) (MI, 0.66 ± 0.13 and 0.78 ± 0.07 ms/mmHg; SH, 1.27 ± 0.16 and 1.48 ± 0.14 ms/mmHg, respectively; P < 0.05 MI vs. SH). At 56 days after MI, BRS was normalized. RB was unaffected by atropine 3 and 28 days after MI but reduced in all other groups. The increase of basal HR by atropine 3 and 28 days after MI was less than in all other groups. HRV (SD of mean N-N interval, coefficient of variance, low- and high-frequency power; studied at 28 and 56 days) was similar in all groups. It is concluded that BRS is transiently depressed in rats with left ventricular dysfunction after MI probably due to a reduced reflex vagal activity. Even though basal HR and HRV are unchanged after MI, a temporary attenuation of tonic vagal activity is unmasked after autonomic blockade.