bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin II stimulates NADH and NADPH oxidase activity in cultured vascular smooth muscle cells.
Authors: Griendling K K , Minieri C A , Ollerenshaw J D , Alexander R W
Published: June 2012

The signaling pathways involved in the long-term metabolic effects of angiotensin II (Ang II) in vascular smooth muscle cells are incompletely understood but include the generation of molecules likely to affect oxidase activity. We examined the ability of Ang II to stimulate superoxide anion formation and investigated the identity of the oxidases responsible for its production. Treatment of vascular smooth muscle cells with Ang II for 4 to 6 hours caused a 2.7 +/- 0.4-fold increase in intracellular superoxide anion formation as detected by lucigenin assay. This superoxide appeared to result from activation of both the NADPH and NADH oxidases. NADPH oxidase activity increased from 3.23 +/- 0.61 to 11.80 +/- 1.72 nmol O2-/min per milligram protein after 4 hours of Ang II, whereas NADH oxidase activity increased from 16.76 +/- 2.13 to 45.00 +/- 4.57 nmol O2-/min per milligram protein. The NADPH oxidase activity was stimulated by exogenous phosphatidic and arachidonic acids and was partially inhibited by the specific inhibitor diphenylene iodinium. NADH oxidase activity was increased by arachidonic and linoleic acids, was insensitive to exogenous phosphatidic acid, and was inhibited by high concentrations of quinacrine. Both of these oxidases appear to reside in the plasma membrane, on the basis of migration of the activity after cellular fractionation and their apparent insensitivity to the mitochondrial poison KCN. These observations suggest that Ang II specifically activates enzyme systems that promote superoxide generation and raise the possibility that these pathways function as second messengers for long-term responses, such as hypertrophy or hyperplasia.
Acidemia and hypernatremia enhance postischemic recovery of excitation-contraction coupling.
Authors: Harada K , Franklin A , Johnson R G , Grossman W , Morgan J P
Published: June 2012

The purpose of the present study was to determine whether Na(+)-H+ and Na(+)-Ca2+ exchanges modulate postischemic recovery of excitation-contraction coupling. Experiments were performed in 43 isolated isovolumic dog hearts perfused with blood (pH 7.40, 141 mmol/L Na+, 34 degrees C, paced at 2 Hz). A 3 x 3-mm region at the left ventricular (LV) apex was loaded with aequorin for monitoring [Ca2+]i simultaneously with LV pressure. No-flow ischemia for 2 to 3 minutes was followed by 20 minutes of aerobic reperfusion with (1) unmodified control blood (141 mmol/L Na+, pH 7.40), (2) acidemic blood (141 mmol/L Na+, pH 6.60, at 0 to 3 minutes of reperfusion), (3) hypernatremic blood (149 or 157 mmol/L Na+, pH 7.40, at 0 to 20 minutes of reperfusion), or (4) hyperosmotic blood (141 mmol/L Na+ + 30 mmol/L mannitol, pH 7.40, at 0 to 20 minutes of reperfusion). Reperfusion with unmodified control blood was immediately followed by an increase in [Ca2+]i and LV systolic and diastolic pressure that persisted for 2 to 3 minutes before returning to or below baseline. Ventricular arrhythmia occurred during this period (> 80%). This transient increase of [Ca2+]i was attenuated by acidemic or hypernatremic perfusate. With acidemic or hypernatremic reperfusion, recovery of LV developed pressure at 20 minutes was more complete than with unmodified control reperfusion: acidemic blood (n = 7), 93 +/- 3% (P < .01); hypernatremic blood (149 mmol/L Na+, n = 7), 89 +/- 2% (P < .02); hypernatremic blood (157 mmol/L Na+, n = 4), 91 +/- 2% (P < .01); and unmodified control blood (n = 17), 80 +/- 2%. With hyperosmotic reperfusion, recovery of LV developed pressure at 20 minutes was not improved (82 +/- 3%). From these results we conclude that (1) an increase in intracellular Ca2+ occurs transiently after no-flow ischemia and may cause arrhythmia and decreased Ca2+ responsiveness of the contractile elements, (2) acidemic and hypernatremic reperfusion ameliorates postischemic dysfunction by preventing the increase in intracellular Ca2+, suggesting that (3) Na(+)-H+ and Na(+)-Ca2+ exchange may play important modulatory roles during reperfusion.
Protein kinase-dependent Cl- currents in feline ventricular myocytes.
Authors: Zhang K , Barrington P L , Martin R L , Ten Eick R E
Published: June 2012

A Cl- current (ICl) induced by isoproterenol (ISO) has been identified in isolated guinea pig ventricular myocytes. This ISO-induced ICl can be inhibited by propranolol and mimicked by forskolin (FSK), suggesting that beta-receptors, cAMP, and protein kinase A (PKA) are involved in regulating the involved Cl- channel. Because activation of protein kinase C (PKC) mediated via alpha-adrenergic receptor stimulation is also known to regulate several ion channels, the idea that activation of PKC also can induce ICl was investigated by using isolated feline ventricular myocytes and the whole-cell patch-clamp technique. We found that extracellularly applied phorbol 12-myristate 13-acetate (PMA) could activate ICl in feline ventricular cells. Control experiments indicated that in the absence of PMA or other interventions, the steady-state current-voltage relation of patches maintained for more than 40 minutes was unchanged over a voltage range from -100 to +80 mV. This suggests that the present findings are not complicated by the development over time after patching of a steady-state ICl, similar to the findings reported for canine atrial myocytes. When induced by PMA, ICl was noninactivating and outwardly rectifying; it reversed polarity at approximately the equilibrium potential for Cl- and was sensitive to the Cl- channel blocker 9-anthracene carboxylic acid. In contrast, PMA failed to induce ICl when either staurosporine or calphostin C was added to the patch pipette solution used to internally dialyze the myocytes. The kinetic properties of PMA- and FSK-induced ICl were similar. When supramaximal concentrations of both ISO (1 mumol/L) and PMA (6 mumol/L) were applied simultaneously, the size of the induced ICl was the same as that induced by the same concentrations of either agonist applied alone. In addition, maximal induction of ICl with PMA (6 mumol/L) prevented the effects of FSK (1 mumol/L, the concentration causing approximately 40% of the maximal response [approximately EC40]), yet the effects of simultaneously applied submaximal concentrations (eg, approximately EC25 to approximately EC40) of both 0.5 mumol/L PMA and 1 mumol/L FSK were roughly additive. The results suggest that (1) both PMA and ISO or FSK can induce ICl with approximately equal efficacy, (2) the PMA- and ISO- or FSK-induced ICls are similar, and (3) they all flow through the same set of Cl- channels, implying that channel phosphorylation via either PKA or PKC can activate this feline cardiac ICl.
Selective inhibition of T-type Ca2+ channels by Ro 40-5967.
Authors: Mishra S K , Hermsmeyer K
Published: June 2012

The present study shows that the chemically novel nondihydropyridine Ca2+ antagonist, Ro 40-5967, blocks T-type divalent ion currents in vascular muscle cells. T-type Ca2+ channels were blocked selectively and completely by therapeutic concentrations of 1 to 10 mumol/L Ro 40-5967, at which there was only 25% to 70% block of L-type Ca2+ currents. Using the combination of Ro 40-5967 and nisoldipine, a dihydropyridine selective for L-type Ca2+ channels, we found that all Ca2+ current could be completely blocked; thus, Ro 40-5967 is the first Ca2+ channel blocker to eliminate dihydropyridine-insensitive voltage-dependent Ca2+ current at therapeutically useful concentrations. The stepwise sequential block of T- and L-type Ca2+ currents demonstrated in the present study fulfills the functional criterion for the separate identity of the two Ca2+ channel types, and introduces a pharmacological tool that promises to be important in the exploration of T-type Ca2+ channel function.
Transforming growth factor-beta 1 potentiated alpha 1-adrenergic and stretch-induced c-fos mRNA expression in rat myocardial cells.
Authors: Miki N , Hamamori Y , Hirata K , Suematsu M , Kawashima S , Akita H , Yokoyama M
Published: June 2012

Since transforming growth factor-beta 1 (TGF-beta 1) has been recently shown to be expressed in the heart by mechanical stretch and ischemic injury, we examined the modulation of c-fos mRNA expression and amino acid uptake by TGF-beta 1 in rat myocardial cells. Pretreatment with TGF-beta 1 potentiated norepinephrine (NE)-induced and stretch-induced (+10% and +20% elongation, for 30 minutes) c-fos mRNA expression by 2.2-fold, whereas TGF-beta 1 alone did not induce c-fos mRNA expression in Northern blot analysis. NE-induced [14C]phenylalanine uptake was also potentiated with TGF-beta 1 pretreatment. The effect of TGF-beta 1 on the NE action was not blocked by propranolol but by prazosin. The protein kinase C activators (12-O-tetradecanoylphorbol 13-acetate [TPA], phorbol 12,13-dibutyrate, and 1-oleyl-2-acetyl-rac-glycerol) induced c-fos mRNA expression, which was also potentiated by TGF-beta 1. Cycloheximide (protein synthesis inhibitor) could not suppress the TGF-beta 1 actions. In nonmuscle cells, TGF-beta 1 modified neither adrenergic nor TPA-induced c-fos mRNA expression. These data suggested that TGF-beta 1 potentiated the c-fos mRNA expression and amino acid incorporation by modification of the alpha 1-adrenergic and stretch-activated protein kinase C pathway. This mechanism did not require protein synthesis.
Glibenclamide enhances but pinacidil reduces attenuation in sympathetic responsiveness after acute coronary artery occlusion.
Authors: Ito M , Pride H P , Zipes D P
Published: June 2012

To investigate the role of ATP-sensitive K+ channels in modulating the efferent autonomic response following acute myocardial ischemia/infarction, we examined the effects of a blocker (glibenclamide) and an opener (pinacidil) of ATP-sensitive K+ channels on the time course and extent of the attenuation in efferent cardiac sympathetic responsiveness in anesthetized dogs. We measured the effective refractory periods (ERPs) at nonischemic sites basal and apical to the area of myocardial ischemia/infarction in the baseline state and during bilateral stimulation of the ansae subclaviae before and after each drug administration and 5, 30, 60, 120, and 180 minutes after latex injection of a diagonal branch of the left anterior descending coronary artery. Animals received either vehicle (n = 12), glibenclamide (0.3 mg.kg-1, n = 10), pinacidil (0.15 mg.kg-1 + 0.2 mg.kg-1 infusion, n = 10), or a combination of these two drugs (n = 9) intravenously. In another group of dogs receiving just pinacidil (n = 10), an intra-aortic balloon was inflated distal to the renal arteries to prevent pinacidil-induced hypotension. Another group of dogs received either high-dose glibenclamide (0.3 mg.kg-1 + 0.15 mg.kg-1, n = 4), low-dose glibenclamide (0.06 mg.kg-1, n = 4), medium-dose pinacidil (0.03 mg.kg-1 + 0.04 mg.kg-1 infusion, n = 4), or low-dose pinacidil (0.0075 mg.kg-1 + 0.01 mg.kg-1 infusion, n = 4). In all dogs, basal sites exhibited no attenuation of sympathetically induced shortening of the ERP throughout the period of acute myocardial ischemia/infarction. Cumulative attenuation in sympathetic responsiveness (shortening of ERP < or = 2 milliseconds induced by bilateral stimulation of the ansae subclaviae) at nonischemic test sites apical to the area of ischemia/infarction during a 3-hour period was greater in the glibenclamide group (26 of 44 sites, P = .008) and less in the pinacidil (2 of 44 sites, P = .002) and pinacidil-balloon (1 of 48 sites, P < .001) groups compared with the vehicle group (14 of 46 sites). Glibenclamide abolished the protective effect of pinacidil so that 10 of 45 sites had < 2-millisecond shortening during a 3-hour period in the glibenclamide + pinacidil group (P = .018 versus pinacidil group, P = .286 versus vehicle group). Such effects of glibenclamide and pinacidil on sympathetic attenuation were dose dependent. Maintaining the blood glucose level during glibenclamide administration did not affect the sympathetic attenuation after acute coronary artery occlusion.(ABSTRACT TRUNCATED AT 400 WORDS)
Diameters of subendocardial arterioles and venules during prolonged diastole in canine left ventricles.
Authors: Hiramatsu O , Goto M , Yada T , Kimura A , Tachibana H , Ogasawara Y , Tsujioka K , Kajiya F
Published: June 2012

Using a needle-probe videomicroscope with a charge-coupled device (CCD) camera, we measured the diameter of subendocardial arterioles and venules during prolonged diastole beyond the time point at which coronary blood flow reached zero. In seven open-chest heart-blocked dogs, a sheathed needle probe with a doughnut-shaped balloon was introduced from the left atrial appendage and advanced into the left ventricle through the mitral valve. The tip of the probe was placed gently on the endocardial surface. Diameters of arterioles (n = 16) and venules (n = 16) at the beginning of long diastole ranged from 40 to 126 microns and from 32 to 192 microns, respectively. After cardiac arrest, the arteriolar diameter gradually declined with aortic pressure. Arteriolar diameters at zero flow decreased by 28 +/- 9% (mean +/- SD) compared with the initial diameter (P < .01). However, none of the subendocardial arterioles collapsed at zero flow or at 12 seconds after the beginning of prolonged diastole (8 to 9 seconds after zero flow) in an additional experiment (n = 5). In contrast to arteriolar diameter, venular diameter increased during prolonged diastole. Venular diameter at zero flow increased by 14 +/- 12% compared with the initial diameter (P < .01). We conclude that during prolonged diastole, when coronary arterial inflow ceases, subendocardial arteriolar diameter decreases without any visible collapse, whereas venular diameter increases.
Targeted ablation of the phospholamban gene is associated with markedly enhanced myocardial contractility and loss of beta-agonist stimulation.
Authors: Luo W , Grupp I L , Harrer J , Ponniah S , Grupp G , Duffy J J , Doetschman T , Kranias E G
Published: June 2012

Phospholamban is the regulator of the Ca(2+)-ATPase in cardiac sarcoplasmic reticulum (SR), and it has been suggested to be an important determinant in the inotropic responses of the heart to beta-adrenergic stimulation. To determine the role of phospholamban in vivo, the gene coding for this protein was targeted in murine embryonic stem cells, and mice deficient in phospholamban were generated. The phospholamban-deficient mice showed no gross developmental abnormalities but exhibited enhanced myocardial performance without changes in heart rate. The time to peak pressure and the time to half-relaxation were significantly shorter in phospholamban-deficient mice compared with their wild-type homozygous littermates as assessed in work-performing mouse heart preparations under identical venous returns, afterloads, and heart rates. The first derivatives of intraventricular pressure (+/- dP/dt) were also significantly elevated, and this was associated with an increase in the affinity of the SR Ca(2+)-ATPase for Ca2+ in the phospholamban-deficient hearts. Baseline levels of these parameters in the phospholamban-deficient hearts were equal to those observed in hearts of wild-type littermates maximally stimulated with the beta-agonist isoproterenol. These findings indicate that phospholamban acts as a critical repressor of basal myocardial contractility and may be the key phosphoprotein in mediating the heart's contractile responses to beta-adrenergic agonists.
Immunohistochemical identification of arteriolar development using markers of smooth muscle differentiation. Evidence that capillary arterialization proceeds from terminal arterioles.
Authors: Price R J , Owens G K , Skalak T C
Published: June 2012

Arteriolar growth is an important event in the adaptation of normal tissues as well as in important pathologies, but the site of origin of new arterioles remains unknown. The network pattern of arteriolar development in skeletal muscle was detected by use of a new immunohistochemical technique that is based on the observation that fully differentiated (mature) vascular smooth muscle (SM) cells express both SM alpha-actin and the two myosin heavy chains (MHCs) SM-1 and SM-2, whereas less differentiated (immature) vascular SM cells do not express MHC. The anterior gracilis muscle microvasculatures of 4- and 9-week-old Sprague-Dawley rats were labeled with monoclonal antibodies to SM alpha-actin and to SM MHC. Whole transverse arteriole networks were observed, and terminal arterioles, defined as terminal segments labeled with SM alpha-actin, were classified on the basis of the presence or absence of SM MHC. A significantly different percentage of terminal arteriolar endings per network without SM MHC was observed in the two groups (66.1 +/- 17.3% for 4 weeks and 27.1 +/- 18.5% for 9 weeks), suggesting that arteriolar development is more nearly complete in the older animals. Sparsely distributed capillaries exhibited thin extensions of SM alpha-actin that crossed collecting venules and joined similar extensions from an adjacent transverse arteriole, effectively forming the basis for new arcade arterioles. SM alpha-actin and SM MHC labeling in terminal arterioles was always continuous with upstream arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of blood-brain barrier endothelial cells by nitric oxide.
Authors: Janigro D , West G A , Nguyen T S , Winn H R
Published: June 2012

Nitric oxide (NO) synthesized by vascular endothelial cells is a potent vasodilator substance. The actions of NO extend well beyond its vasodilatory properties, and increasingly, NO has been recognized as an important signal for intercellular and intracellular communication. Recently, NO has been implicated in the regulation of vascular and blood-brain barrier permeability. NO has also been shown to modulate ion channels in excitable cells, thus affecting neuronal firing. We report the results of patch-clamp experiments that show a modulatory action of NO as well as cGMP and cAMP on a hyperpolarization-activated current (Iha) carried by both Na+ and K+ ions in blood-brain barrier endothelial cells. Iha was recorded in cells dialyzed with 0.2 mmol/L GTP-gamma-S to inhibit a large inwardly rectifying potassium current. This ionic current and its modulation by NO may play a role in the regulation of the transport of ions, nutrients, and other molecules to the brain and serve as an integral part of the blood-brain barrier. The modulation of Iha by a cyclic guanosine nucleotide may also explain previous reports suggesting a role for NO in the regulation of blood-brain barrier function.
Endomyocardial gene expression during development of pacing tachycardia-induced heart failure in the dog.
Authors: Williams R E , Kass D A , Kawagoe Y , Pak P , Tunin R S , Shah R , Hwang A , Feldman A M
Published: June 2012

Selective and specific changes in gene expression characterize the end-stage failing heart. However, the pattern and relation of these changes to evolving systolic and diastolic dysfunction during development of heart failure remains undefined. In the present study, we assessed steady-state levels of mRNAs encoding a group of cardiac proteins during the early development of left ventricular dysfunction in dogs with pacing-induced cardiomyopathy. Corresponding hemodynamic assessments were made in the conscious state in the same animals and at the same time points at baseline, after 1 week of ventricular pacing, and at the onset of clinical heart failure. Systolic dysfunction dominated after 1 week of pacing, whereas diastolic dysfunction was far more pronounced with the onset of heart failure. Atrial natriuretic factor mRNA was undetectable in 7 of 12 hearts at baseline but was expressed in all hearts at 1 week (P < .01 by chi 2 test), and it increased markedly with progression to failure (P = .05). Creatine kinase-B mRNA also rose markedly with heart failure (P < .01). Levels of mRNA encoding beta-myosin heavy chain, mitochondrial creatine kinase, phospholamban, and sarcoplasmic reticulum Ca(2+)-ATPase did not significantly change from baseline, despite development of heart failure. Additional analysis to determine if these mRNA changes were related to the severity of diastolic or systolic dysfunction revealed that phospholamban mRNA decreased in hearts with larger net increases in end-diastolic pressure (+19.2 +/- 1.9 mm Hg) compared with those hearts in which it did not change (+4.0 +/- 4.9, P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)
Increase of the delayed rectifier K+ and Na(+)-K+ pump currents by hypotonic solutions in guinea pig cardiac myocytes.
Authors: Sasaki N , Mitsuiye T , Wang Z , Noma A
Published: June 2012

To investigate the membrane current changes induced by membrane stretching, single guinea pig ventricular myocytes were superfused with solutions of various osmolarities, and the whole-cell current was recorded by the patch-clamp technique. The application of 70% and 130% osmolar bath solutions increased and decreased the amplitude of delayed rectifier K+ current (IK), respectively, whereas no obvious change was observed in the L-type Ca2+ current or the inward rectifier K+ current. When the Na(+)-K+ pump current (Ipump) was recorded by the use of high-Na+ (> 35 mmol/L) pipette solutions, Ipump was also increased and decreased by the superfusion of hypotonic and hypertonic solutions, respectively, in approximately half of the cells. An increase of the Ipump was also observed in the absence of external Na+, excluding a possibility that the enhancement of Ipump was secondary to an elevation of cytosolic Na+. In most cells that did not show the increase of Ipump, the hypotonic superfusion induced a gradual activation of Cl- current. The hypertonic superfusion did not cause any consistent change in the membrane Cl- conductance. Since the response of IK was observed in all experiments, its mechanism was studied. We failed to observe marked changes in the kinetic and conductance properties of IK in the hypotonic solution. The involvements of either the protein kinases or Ca2+ were also ruled out as major mechanisms underlying the IK response.
Characterization of thrombin receptor expression during vascular lesion formation.
Authors: Wilcox J N , Rodriguez J , Subramanian R , Ollerenshaw J , Zhong C , Hayzer D J , Horaist C , Hanson S R , Lumsden A , Salam T A
Published: June 2012

Blood vessels respond to injury by initiating cell proliferation and migration that result in vascular lesion formation. To determine the roles of thrombin and the thrombin receptor in this process, we characterized thrombin receptor expression in normal and injured arteries, thrombin receptor-mediated smooth muscle cell mitogenesis, and the regulation of thrombin receptor mRNA expression in vitro. Thrombin receptor mRNA was not detected in normal rat or baboon arteries by in situ hybridization. Immunohistochemistry using an antithrombin receptor antibody (TR-R9), directed against the thrombin cleavage site of the rat aortic smooth muscle cell thrombin receptor, revealed low-level staining for thrombin receptor protein in endothelial cells and smooth muscle cells of normal arteries. In contrast, balloon catheter injury increased thrombin mRNA expression in medial smooth muscle cells within 6 hours. This increased thrombin receptor expression continued within the media and in neointimal cells throughout vascular lesion formation, predominantly in areas of active cell proliferation. In vitro, alpha-thrombin stimulates rat aortic smooth muscle cell proliferation in a concentration-dependent manner. That thrombin receptor activation is required for the mitogenic response was confirmed by demonstrating that the polyclonal antibody TR-R9 inhibits thrombin-induced cell proliferation. Thrombin receptor mRNA synthesis was induced by both basic fibroblast growth factor (maximal stimulation of 1.8-fold at 1 hour) and platelet-derived growth factor (maximal stimulation of 2.4-fold at 8 and 24 hours) in quiesced cultured rat aortic smooth muscle cells. In summary, upregulation of smooth muscle cell thrombin receptor expression occurs very early after vascular injury and continues throughout neointimal development.(ABSTRACT TRUNCATED AT 250 WORDS)
E-selectin ligands mediate tumor necrosis factor-induced neutrophil sequestration and pulmonary edema in guinea pig lungs.
Authors: Lo S K , Bevilacqua B , Malik A B
Published: June 2012

We have previously shown in perfused guinea pig lungs that tumor necrosis factor-alpha (TNF-alpha) pretreatment of lungs enhanced neutrophil sequestration as reflected by a 2.4-fold increase in lung myeloperoxidase (MPO) activity. Subsequent perfusion of phorbol 12-myristate 13-acetate (PMA) to activate the sequestered neutrophils produced an approximately threefold increase in the pulmonary capillary hydrostatic pressure and fulminant pulmonary edema. Using this ex vivo model of lung injury, we studied the role of three putative E-selectin ligands, sialyl-Lewis X, Lewis X, and dimeric sialyl-Lewis X, in mediating neutrophil sequestration and pulmonary edema. We pretreated neutrophils with monoclonal antibodies (mAbs) directed against these E-selectin ligands. Pretreatment of neutrophils with mAbs to sialyl-Lewis X and Lewis X reduced the neutrophil sequestration, as evidenced by 45% and 27% reductions in MPO activity from control levels, respectively. This occurred in parallel with inhibition of neutrophil adhesion to the TNF-alpha-activated endothelial cells in vitro. The mAbs to dimeric sialyl-Lewis X and an isotype-matched control mAb against lactosamines present on neutrophils had no effect on lung MPO activity and neutrophil adhesion. All mAbs to sialyl-Lewis X, Lewis X, and dimeric sialyl-Lewis X reduced the increases in the pulmonary capillary hydrostatic pressure after challenge of the sequestered neutrophils with PMA and also reduced lung weight gain by 71%, 45% and 38%, respectively. The control mAb to the lactosamines had no effect on the pulmonary capillary hydrostatic pressure and lung weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of an inactivating human cardiac K+ channel by protein kinase C.
Authors: Murray K T , Fahrig S A , Deal K K , Po S S , Hu N N , Snyders D J , Tamkun M M , Bennett P B
Published: June 2012

The transient outward current (ITO) is an important repolarizing component of the cardiac action potential. In native cardiac myocytes, ITO is modulated after activation of protein kinase C, although the molecular nature of this effect is not well understood. A channel recently cloned from human ventricular myocardium (Kv1.4, HK1) produces a rapidly inactivating K+ current, which has phenotypic similarities to the 4-aminopyridine-sensitive component of ITO. Therefore, we examined whether this recombinant channel was also modulated by protein kinase C activation by investigating the effects of the diacylglycerol analogue phorbol 12-myristate 13-acetate (PMA) on Kv1.4 K+ current expressed in Xenopus oocytes. At a concentration of 10 nmol/L, PMA caused a biphasic response with an initial increase (14 +/- 4%, mean +/- SEM) in current, which peaked in 14 minutes. This was followed by a significant reduction (40 +/- 11%) in the current within 30 minutes. There was no significant change in cell membrane electrical capacitance with 10 nmol/L PMA (1 +/- 1% decline in 30 minutes), demonstrating that loss of cell membrane surface area did not explain the reduction in K+ current, although cell capacitance did decrease when using a higher concentration of PMA (81 nmol/L). The inactive stereoisomer, 4 alpha-PMA, had no effect on Kv1.4 current, whereas preincubation with the protein kinase inhibitor staurosporine or protein kinase C-selective chelerythrine prevented the effects of PMA. When purified from a stably transfected mammalian cell line by using immunoprecipitation, the channel protein was readily phosphorylated in vitro by purified protein kinase C.(ABSTRACT TRUNCATED AT 250 WORDS)
Central Command Increases Muscle Sympathetic Nerve Activity During Intense Intermittent Isometric Exercise in Humans
Authors: Victor Ronald G. , Secher Niels H. , Lyson Teresa , Mitchell Jere H.
Published: June 2012

Abstract
During sustained isometric exercise, central command has very little effect on muscle sympathetic nerve activity (MSNA). To determine if central command has a greater effect on MSNA during intermittent than during sustained contractions, MSNA was recorded with microelectrodes (peroneal nerve) during intermittent isometric handgrip at 25%, 50%, and 75% maximum voluntary contraction (MVC) in 9 human subjects with paced breathing. Similar experiments were performed in 11 additional subjects before and after partial neuromuscular blockade (intravenous curare) to isolate the influence of central command while minimizing force output and thus muscle afferent feedback. Before curare, handgrip at 25% and 50% MVC had no effect on MSNA, whereas handgrip at 75% MVC synchronized the MSNA to the handgrip such that MSNA was 5.7±1.3 times higher (mean±SEM,
P
<.001) during the contraction periods than during the relaxation periods. After curare, this synchronization of MSNA persisted without attenuation, even though force output fell to <25% of the initial MVC. From these observations, we conclude that central command causes synchronization of motor activity and muscle sympathetic activity during intense intermittent isometric exercise.
Systolic Flow Augmentation in Hearts Ejecting Into a Model of Stiff Aging Vasculature
Authors: Saeki Akio , Recchia Fabio , Kass David A.
Published: June 2012

Abstract
Age-related arterial stiffening and widening of the pulse pressure elevates ventricular systolic wall stress while it lowers diastolic coronary perfusion pressure. These changes are thought to adversely alter the balance between myocardial work load and blood supply. To test this hypothesis, the native compliant thoracic aorta was surgically bypassed by a stiff tube in reflex-blocked anesthetized dogs. Ventricular outflow was directed into either native aorta or the bypass; the latter resulting in an increase in arterial pulse pressure from 37.8 to 107.5 mm Hg (
P
<.001), with minimal change in mean pressure and flow. Cardiac work load was assessed by pressure-volume area (PVA), which combines external and internal left ventricular work and is linearly related to myocardial oxygen consumption (MV̇
o
2
), and by MV̇
o
2
itself. Regional phasic and mean coronary flow were measured in the left anterior descending coronary artery, and global flow was assessed by radiolabeled microspheres. Myocardial supply-demand balance was assessed by comparing flow at matched PVA or MV̇
o
2
, flow-PVA relations, and endocardial-to-epicardial flow ratios. When blood flow was directed into the stiff bypass tube, peak systolic pressure, wall stress, and PVA all rose nearly 50%, yet diastolic perfusion pressure fell by 20 mm Hg (all
P
<.01). Rather than being compromised, however, mean coronary flow rose by 34%, maintaining the same endocardial-to-epicardial flow ratio (≈1.1). Flow augmentation persisted when data were compared at matched work load (PVA or MV̇
o
2
) and mean arterial pressure, as well as over a range of work loads (
P
<.001 from ANCOVA of flow-PVA relations). The increased flow resulted from enhanced systolic perfusion, which nearly equaled diastolic flow when ejection passed into the stiff bypass. These data counter the notion that cardiac coupling with a stiff arterial system (as with aging) necessarily compromises myocardial flow versus metabolic demand. However, the data highlight a greater role of systolic flow under such conditions and also raise the novel suggestion that enhanced pulsatility of the arterial pressure waveform may itself augment coronary perfusion.
β
2
-Adrenergic Receptor Actions in Neonatal and Adult Rat Ventricular Myocytes
Authors: Kuznetsov Valiery , Pak Elena , Robinson Richard B. , Steinberg Susan F.
Published: June 2012

Abstract
The physiological function of β
2
-adrenergic receptors in the neonatal and adult heart is incompletely understood, and possible age-dependent differences in β
2
-receptor actions have not been considered. We used isoproterenol (mixed β
1
- and β
2
-receptor agonist) and zinterol (β
2
-selective agonist) to compare β-receptor subtype actions in neonatal and adult rat ventricular myocytes. When delivered as a bolus at a final concentration of 10
−7
mol/L, both isoproterenol and zinterol increased the amplitude and hastened the kinetics of the calcium and cell-shortening transients in neonatal myocytes. Under identical experimental conditions, isoproterenol increased the amplitude and accelerated the kinetics of the calcium transient and the twitch in adult myocytes, whereas zinterol did not. In the presence of CGP 20712A (β
1
-receptor blocker), a 100-fold higher concentration of zinterol increased the amplitude but prolonged the duration of the twitch in adult myocytes. To probe the mechanism for this age-dependent difference in β
2
-receptor responsiveness, we compared β-receptor expression and stimulation of cAMP accumulation in neonatal and adult myocytes. β-Receptor density was 44 339±5178 sites per cell in neonatal myocytes and 186 346±13 356 sites per cell in adult myocytes; the relative proportion of β
2
-receptors was comparable in each (16.7±2.3% and 16.9±0.9%, respectively). Isoproterenol induced a large increase in cAMP accumulation in neonatal and adult myocytes (20.0±1.0- and 20.6±2.6-fold over basal). In contrast, zinterol evoked a substantial increase in cAMP accumulation in neonatal myocytes but only a minor increase in adult myocytes. These studies provide evidence that at low agonist concentrations, β
2
-receptor activation contributes to the positive inotropic response by increasing cAMP and increasing the amplitude and hastening the kinetics of the twitch in neonatal, but not adult, myocytes. Moreover, these results suggest that age-dependent differences in β
2
-receptor coupling to more distal elements in the signaling cascade can influence myocyte β
2
-receptor responsiveness.
Activation of Mitogen-Activated Protein Kinase in Porcine Carotid Arteries
Authors: Adam Leonard P. , Franklin Michael T. , Raff Gregory J. , Hathaway David R.
Published: June 2012

Abstract
The thin-filament protein h-caldesmon (the high molecular weight isoform of caldesmon) is phosphorylated in resting and contracted porcine carotid arteries. Phosphorylation of h-caldesmon in intact tissue occurs at sites that are covalently modified by mitogen-activated protein kinase (MAPK) in vitro. In this study, we have evaluated MAPK activation in arteries in response to mechanical load and pharmacological stimulation. MAPK was extracted from resting and stimulated porcine carotid arteries and then partially purified by anion-exchange fast-performance liquid chromatography. MAPK activity was separated into two peaks corresponding to the tyrosine-phosphorylated 42- and 44-kD isoforms of MAPK (p42
MAPK
and p44
MAPK
, respectively). Of the total MAPK activity, 42% was associated with p42
MAPK
, and 58% was associated with p44
MAPK
; this percentage was not altered by stimulation of the muscles with either KCl (110 mmol/L) or phorbol 12,13-dibutyrate (PDBu, 1 μmol/L). Both p42
MAPK
and p44
MAPK
, purified from porcine carotid arteries, phosphorylated h-caldesmon at the same sites and to levels approaching or >1 mol phosphate per mole protein. In unloaded muscle strips, MAPK activity was 39 pmol · min
−1
· mg protein
−1
when assayed with the peptide substrate APRTPGGRR. MAPK activity increased in response to incremental mechanical loading to a maximum of 99 pmol · min
−1
· mg protein
−1
at 16×10
3
N/m
2
. MAPK activity could be further increased in loaded muscles by pharmacological stimulation. With KCl stimulation, MAPK activities rose to a peak of 205 pmol · min
−1
· mg protein
−1
at 10 minutes and then declined to basal values at 30 and 60 minutes. Stimulation with PDBu induced a gradual increase in MAPK activity that reached a value of 201 pmol · min
−1
· mg protein
−1
at 60 minutes. These results demonstrate that the level of MAPK activity in vascular smooth muscle is regulated in response to both mechanical load and pharmacological stimulation. Activation of MAPK and the subsequent phosphorylation of h-caldesmon may be important processes that modulate vascular smooth muscle contractility.
Integrin-Mediated Collagen Matrix Reorganization by Cultured Human Vascular Smooth Muscle Cells
Authors: Lee Richard T. , Berditchevski Fedor , Cheng George C. , Hemler Martin E.
Published: June 2012

Abstract
Vascular smooth muscle cells perform the important function of modulation of vascular extracellular matrix. Because integrins mediate many cell-matrix interactions, the role of integrins in reorganization of collagen by cultured human vascular smooth muscle cells was studied. Immunoprecipitation demonstrated that human vascular smooth muscle cells express multiple β
1
integrins. Monoclonal antibody A2-IIE10 (a blocking anti-α
2
antibody) inhibited adhesion of smooth muscle cells to collagen by 31%. The blocking anti-α
1
antibody 1B3.1 inhibited adhesion by 40%, whereas a blocking anti-α
3
antibody had no effect on adhesion. When 1B3.1 and A2-IIE10 were both used, a 79% reduction in adhesion was observed, indicating that active α
1
and α
2
integrins cooperatively mediate adhesion. The blocking anti-β
1
antibody Mab13 abolished smooth muscle cell–mediated gel contraction, and the α
2
-blocking antibody A2-IIE10 had a dose-dependent partial inhibitory effect (37%). In contrast, blocking antibodies to α
1
and α
3
had no effect. When anti-α
1
(1B3.1) and anti-α
2
(A2-IIE10) monoclonal antibodies were combined, no synergistic effect on inhibition of gel contraction was observed. Surprisingly, collagen gel contraction was inhibited by 46% by an anti-β
1
antibody (TS2/16) known for its stimulatory effect on cell adhesion. Thus, whereas α
1
β
1
and α
2
β
1
integrins both participate in adhesion of vascular smooth muscle cells to collagen, only α
2
β
1
integrins mediate collagen reorganization. In addition, collagen reorganization appears to be a dynamic process, adversely affected by excessive adhesion strengthening.
Propafenone Preferentially Blocks the Rapidly Activating Component of Delayed Rectifier K
+
Current in Guinea Pig Ventricular Myocytes
Authors: Delpón Eva , Valenzuela Carmen , Pérez Onésima , Casis Oscar , Tamargo Juan
Published: June 2012

Abstract
The effects of propafenone on the delayed rectifier K
+
current were studied in guinea pig ventricular myocytes by using the patch-clamp technique. In these myocytes, this current consists of at least two components: a La
3+
-sensitive component activating rapidly with moderate depolarizations and a La
3+
-resistant current slowly activating at more positive potentials. In the absence of La
3+
(when both components are present), propafenone inhibited the delayed outward current, its effects being more marked after weak than after strong depolarizations. Propafenone-induced block of the tail currents elicited on return to −30 mV was more marked after short than after long depolarizing pulses. In the presence of 1 μmol/L propafenone, the envelope-of-tails test was satisfied, thus indicating that at this concentration propafenone completely blocks the rapidly activating component. In the presence of La
3+
(when only the slow component is present), the steady state inhibition induced by 5 μmol/L propafenone on both the maximum activated and the tail currents was independent of the test pulse voltage. Development of propafenone-induced block on the slowly activating component was very fast and linked to channel opening. In addition, the blockade appeared to be use dependent, with the rate constant of the onset kinetics at 2 Hz being 0.44±0.1 pulse
−1
. The recovery process from propafenone-induced block exhibited a time constant of 2.5±0.4 s. These results indicated that propafenone preferentially inhibits the rapidly activating component of the delayed rectifier and that it blocks in a voltage-independent and time-dependent manner the slow component of this current.
Effects of Hypoxanthine–Xanthine Oxidase on Ca
2+
Stores and Protein Synthesis in Human Endothelial Cells
Authors: Dreher D. , Jornot L. , Junod A. F.
Published: June 2012

Abstract
We have investigated the effects of reactive O
2
metabolites generated by the hypoxanthine–xanthine oxidase (HX-XO) system on intracellular Ca
2+
and its relation with protein synthesis in human umbilical vein endothelial cells (HUVECs). Spectrofluorometry with fura 2 showed that the oxidative stress induced a rapid transient rise in cytosolic [Ca
2+
], followed by a sustained elevation above the baseline value. In the presence of La
3+
, which blocks Ca
2+
influx from the extracellular medium, a transient [Ca
2+
] increase was still observed, but the sustained rise was suppressed. The HX-XO–related [Ca
2+
] changes were completely prevented by pretreatment with thapsigargin, which depletes intracellular Ca
2+
stores. Hence, the effects of HX-XO on Ca
2+
homeostasis were due to mobilization of Ca
2+
from the intracellular stores with subsequent influx of extracellular Ca
2+
. HX-XO mobilized more of sequestered Ca
2+
than did thrombin, a receptor agonist that depletes only a part of the intracellular Ca
2+
stores (the hormone-sensitive stores). To determine the relevance of the HX-XO–related depletion of Ca
2+
stores for cell function, we investigated the role of Ca
2+
mobilization in the regulation of protein synthesis. Overall protein synthesis in HUVECs was markedly reduced by thapsigargin, which depletes both hormone-sensitive and -insensitive stores, but was not substantially affected by thrombin. Manipulation of the refilling of the Ca
2+
stores via the availability of extracellular Ca
2+
significantly influenced the thapsigargin-related and the HX-XO–related inhibition of overall protein synthesis. A corresponding effect of extracellular [Ca
2+
] was seen in polyribosome distribution profiles, which reflected an inhibition of translation initiation in both treatments. Thus, depletion of Ca
2+
stores appeared to be involved in the inhibition of protein synthesis at the initiation level by both thapsigargin and HX-XO. These results indicate that (1) the cytosolic [Ca
2+
] changes induced by HX-XO result from mobilization of Ca
2+
from intracellular stores and subsequent influx of extracellular Ca
2+
, (2) the HX-XO–related mobilization of sequestered Ca
2+
includes hormone-insensitive pools, and (3) the depletion of hormone-insensitive Ca
2+
stores appears to be in part responsible for the inhibition of protein synthesis by HX-XO.
Protective Role of Bradykinin in Cardiac Anaphylaxis
Authors: Rubin Lisa E. , Levi Roberto
Published: June 2012

Abstract
Cardiac anaphylaxis, an acute ischemic dysfunction comprising coronary vasoconstriction and arrhythmias, is a model of clinically recognized immediate hypersensitivity reactions affecting the heart. Bradykinin, a mediator of hypersensitivity, is also a potent coronary vasodilator, acting via nitric oxide and prostacyclin production. Because ischemia increases bradykinin outflow from the heart, we questioned whether bradykinin might mitigate anaphylactic coronary vasoconstriction. Antigen challenge of hearts isolated from presensitized guinea pigs was associated with an ≈30% increase in bradykinin overflow. Furthermore, (1) when the half-life of bradykinin was prolonged with the kininase II/angiotensin-converting enzyme inhibitors captopril and enalaprilat, anaphylactic coronary vasoconstriction was attenuated and reversed, and arrhythmias were alleviated; (2) the bradykinin B
2
-receptor antagonist HOE 140 prevented these effects; and (3) HOE 140 exacerbated both anaphylactic coronary vasoconstriction and arrhythmias. During cardiac anaphylaxis, the coronary overflow of cGMP, a marker of nitric oxide production, and 6-ketoprostaglandin F
1α
, a stable prostacyclin metabolite, increased twofold and fourfold, respectively. Because neither enalaprilat nor HOE 140 affected these changes, the enhanced overflow of cGMP and 6-ketoprostaglandin F
1α
is likely to reflect the actions of other hypersensitivity mediators (eg, histamine and leukotrienes). We postulate that bradykinin plays a protective role in cardiac anaphylaxis by accumulating at the luminal surface of the coronary endothelium and promoting, in an autocrine mode, a B
2
-receptor–mediated production of nitric oxide and prostacyclin in concentrations sufficient to elicit a paracrine effect on coronary vascular smooth muscle, thus opposing the vasoconstricting effects of other anaphylactic mediators.
Hormonal Dependence of the Effects of Metabolic Encephalopathy on Cerebral Perfusion and Oxygen Utilization in the Rat
Authors: Kozniewska Ewa , Roberts Timothy P. L. , Vexler Zinaida S. , Oseka M. , Kucharczyk John , Arieff Allen I.
Published: June 2012

Abstract
Previous studies have demonstrated that in adult rats with chronic hyponatremia, both symptoms of encephalopathy and mortality largely depend upon the gender of the animal and the presence of elevated plasma levels of vasopressin (AVP). Since effects of AVP on blood vessels may be gender dependent, the present study was designed to compare the effects of chronic (4 days) hyponatremia on cerebral blood flow (CBF), cerebral oxygen consumption (CMRO
2
), and cerebral perfusion index (CPI) in adult male and female rats. CBF (intra-arterial
133
Xe injection method) and CMRO
2
(arteriovenous difference of cerebral oxygen content×CBF) were measured in normonatremic and hyponatremic (hyponatremia induced with 140 mmol/L glucose and either AVP or desmopressin [dDAVP], plasma sodium=100 to 110 mmol/L) adult rats of both genders. The CPI was assessed from magnetic resonance imaging of the transit of magnetic susceptibility contrast agent through the brain. Female rats with AVP-induced chronic hyponatremia had a 36% decrease in CBF and a 60% decrease in CMRO
2
. In male animals, both parameters were not different from control values. AVP-induced hyponatremia resulted in a 45% decrease in CPI in female rats, but hyponatremia induced with dDAVP did not affect CPI in either male or female rats. Chronic (4 days) administration of AVP did not affect CPI in either male or female normonatremic rats. When rats with AVP-induced chronic hyponatremia were pretreated with estrogen, the CPI in males was not different from that in females. Our results demonstrate that during AVP-induced chronic hyponatremia in female rats, there is significant depression of both oxygen utilization and blood flow in the brain.