bluuebunny/crossref_metadata_2025 huggingface dataset:
Age-associated changes in cardiovagal baroreflex sensitivity are related to central arterial compliance
Authors: Monahan Kevin D. , Dinenno Frank A. , Seals Douglas R. , Clevenger Christopher M. , Desouza Christopher A. , Tanaka Hirofumi
Published: December 2017

Cardiovagal baroreflex sensitivity (BRS) declines with advancing age in humans, but the underlying mechanism has not been established. Using two different approaches, we determined the relation between age-associated decline in cardiovagal BRS and the compliance of an artery in which arterial baroreceptors are located. First, we measured carotid artery compliance (via the simultaneous application of ultrasonography and arterial applanation tonometry) and cardiovagal BRS (phase IV of the Valsalva maneuver) in 47 healthy sedentary men that varied widely in age (19–76 yr). Cardiovagal BRS declined progressively with age ( r = −0.69; P ≤ 0.001) and was positively related to carotid artery compliance ( r = 0.71; P ≤ 0.001). Stepwise multiple-regression analysis revealed that carotid artery compliance was the strongest independent physiological correlate of cardiovagal BRS and that it explained 51% of the total variance. Second, we studied 13 middle-aged and older previously sedentary men (age 56 ± 2 yr) before and after 13 wk of aerobic exercise intervention. Regular exercise increased both cardiovagal BRS and carotid artery compliance ( P < 0.05) and the two events were strongly and positively related ( r = 0.72; P < 0.01). We conclude that reduced carotid artery compliance may play an important mechanistic role in age-associated decrease in cardiovagal BRS in healthy sedentary humans.
Cysteinyl leukotrienes mediate enhanced vasoconstriction to angiotensin II but not endothelin-1 in SHR
Authors: Shastri Shailesh , McNeill J. Robert , Wilson Thomas W. , Poduri Ramarao , Kaul Chamanlal , Gopalakrishnan Venkat
Published: December 2017

We assessed whether cysteinyl leukotrienes mediate the vasoconstrictor responses to angiotensin II and endothelin-1 in the mesenteric vascular bed of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) perfused ex vivo at a constant flow rate of 5 ml/min with Krebs buffer. Maximal perfusion pressure response ( Emax) but not EC50values to angiotensin II ( P < 0.001) and endothelin-1 ( P < 0.01) were significantly higher in the SHR, whereas the responses to potassium chloride remained unchanged. Inclusion of the selective 5-lipoxygenase inhibitor AA-861 or the cysteinyl leukotriene receptor antagonist MK-571 significantly reduced the vasoconstrictor responses to angiotensin II but not to endothelin-1 and potassium chloride. The reduction in Emaxto angiotensin II was more pronounced in SHR ( P < 0.001) than in WKY ( P < 0.05) rats. Cysteinyl leukotrienes LTC4-, LTD4-, and LTE4(1 μM)-evoked vasoconstrictor responses were significantly higher in SHR ( P < 0.05), whereas LTB4failed to evoke any response in either strain. These data suggest that 5-lipoxygenase metabolites, particularly cysteinyl leukotrienes, contribute to the exaggerated vasoconstrictor responses to angiotensin II but not to endothelin-1.
Carbon monoxide produced by isolated arterioles attenuates pressure-induced vasoconstriction
Authors: Zhang Fan , Kaide Jun-Ichi , Wei Yuan , Jiang Houli , Yu Changhua , Balazy Michael , Abraham Nader G. , Wang Wenhui , Nasjletti Alberto
Published: December 2017

Studies were conducted on isolated rat gracilis muscle arterioles to examine the role of vascular heme oxygenase (HO)-derived carbon monoxide (CO) on myogenic constrictor responses to stepwise increments in intraluminal pressure. The arterioles express HO-2 but not HO-1 and manufacture CO. Both HO-2 protein expression and CO production are reduced in arterioles maintained for 18 h before experimentation in media containing HO-2 antisense oligodeoxynucleotides (AS-ODN). Pressurization of arterioles mounted on a myograph over the pressure range of 40–100 mmHg elicits reduction of internal diameter. At pressures >40 mmHg, the internal diameter of vessels treated with either HO-2 AS-ODN, the HO inhibitor chromium mesoporphyrin (CrMP), or the K+channel blocker tetraethylammonium (TEA) are smaller than the corresponding control values. The inclusion of exogenous CO, but not of biliverdin, in the superfusion buffer attenuates pressure-induced vasoconstriction in CrMP-treated vessels. However, exogenous CO does not attenuate pressure-induced vasoconstriction in vessels treated with both CrMP and TEA. Collectively, these data suggest that CO of vascular origin attenuates pressure-induced arteriolar constriction via a mechanism involving a TEA-sensitive K+ channel.
Myocardial creatine kinase kinetics and isoform expression in hearts with severe LV hypertrophy
Authors: Ye Yun , Wang Chunsheng , Zhang Jianyi , Cho Young K. , Gong Guangrong , Murakami Yo , Bache Robert J.
Published: December 2017

Left ventricular (LV) hypertrophy (LVH) results in a fetal shift in myocardial creatine kinase (CK) expression. Because CK plays an important role in intracellular energy production, transport, and utilization, this study was performed to characterize changes in CK expression and CK flux in severe pressure-overload LVH. Ascending aortic banding in 8-wk-old dogs resulted in LVH with a 92% increase in relative LV mass. In LVH hearts, CK-M isoform mRNA was decreased by 40% ( P = 0.05) and protein was decreased by 50% ( P < 0.01), whereas mitochondrial CK protein was decreased by 22% ( P < 0.05). CK-B isoform mRNA was undetectable in normal hearts but was prominently expressed in LVH ( P< 0.01); CK-B protein was increased by more than 10-fold in LVH ( P < 0.01). Despite these changes, total CK activity was normal in LVH. Myocardial CK flux was examined using31P magnetic resonance spectroscopy magnetization transfer. The CK forward rate constant was similar in normal and LVH hearts at baseline and did not change in either group during dobutamine treatment. In hearts with LVH, the CK forward flux rate was reduced by ∼60% ( P < 0.05) and decreased further during dobutamine. Thus, although pressure-overload LVH caused alterations of expression of both CK mRNA and protein levels, LV performance and oxygen consumption in response to dobutamine were normal. However, myocardial free ADP was increased in LVH hearts. This finding suggests that the CK alterations result in a need for higher ADP levels to maintain ATP synthesis in the hypertrophied heart.
PTP-ε, a tyrosine phosphatase expressed in endothelium, negatively regulates endothelial cell proliferation
Authors: Thompson Larry J. , Jiang Jihong , Madamanchi Nageswara , Runge Marschall S. , Patterson Cam
Published: December 2017

The vascular endothelium is a dynamic interface between the blood vessel and circulating factors and, as such, plays a critical role in vascular events like inflammation, angiogenesis, and hemostasis. Whereas specific protein tyrosine kinases have been identified in these processes, less is known about their protein tyrosine phosphatase (PTP) counterparts. We utilized a RT-PCR/differential hybridization assay to identify PTP-ε as a highly abundant endothelial cell PTP. PTP-ε mRNA expression is growth factor responsive, suggesting a role for this enzyme in endothelial cell proliferation. Overexpression of PTP-ε decreases proliferation by 60% in human umbilical vein endothelial cells (HUVEC) but not in smooth muscle cells or fibroblasts. In contrast, overexpression of PTP-ε (D284A), a catalytically inactive mutant, has no significant effect on HUVEC proliferation. These data provide the first functional characterization of PTP-ε in endothelial cells and identify a novel pathway that negatively regulates endothelial cell growth. Such a pathway may have important implications in vascular development and angiogenesis.
O2-dependent prostanoid synthesis activates functional PGE receptors on corpus cavernosum smooth muscle
Authors: Moreland Robert B. , Albadawi Hassan , Bratton Charles , Patton George , Goldstein Irwin , Traish Abdulmaged , Watkins Michael T.
Published: December 2017

We have previously demonstrated that decreased O2tension inhibits prostaglandin synthesis from human corpus cavernosum smooth muscle cells in static culture over 8–18 h (R. B. Moreland et al., Molecular Urology 2: 41–47, 1998). In this report, an experimental system was designed that allowed determination of the effects of O2tension changes over the time frame of physiological penile erection. Human corpus cavernosum smooth muscle cells were cultured on microcarrier beads in enclosed stirrer flasks so that rapid changes of O2tension could be modulated. After 18 h of equilibration at 30–40 mmHg to simulate blood Po2at penile flaccidity, O2tension was increased to 100 mmHg for 1 h and then returned to 30–40 mmHg. Media samples were withdrawn for prostanoid synthesis and cell samples were taken for cAMP determinations. After 18 h of 30–40 mmHg Po2values, prostanoid synthesis by human corpus cavernosum smooth muscle cells was low (0.1–0.7 pmol/106cells). When Po2was increased to 100 mmHg, a rapid increase in PGE2>> PGF2α> PGD2was observed (thromboxane A2was undetectable), which peaked at 5.7 pmol PGE2/106cells. Increased O2tension correlated with increased PGE2and increased intracellular synthesis of cAMP. The prostaglandin G/H synthase inhibitor indomethacin or the E prostanoid (EP2)-selective antagonist AH-6809 each inhibited the O2-tension-dependent increases in cAMP. These data support a role of differential O2tension in the penis in the smooth muscle synthesis of PGE2, which in turn increases cAMP synthesis via EP2receptors.
Assessment of LV systolic function in atrial fibrillation using an index of preceding cardiac cycles
Authors: Tabata Tomotsugu , Grimm Richard A. , Greenberg Neil L. , Agler Deborah A. , Mowrey Kent A. , Wallick Don W. , Zhang Youhua , Zhuang Shaowei , Mazgalev Todor N. , Thomas James D.
Published: December 2017

The clinical assessment of left ventricular (LV) systolic function during atrial fibrillation (AF) is unreliable and difficult because of beat-to-beat variability. We evaluated an index for the estimation of LV systolic function in AF that is based on the relationship between the preceding (R-R1) and prepreceding (R-R2) R-R intervals. LV Doppler stroke volume (SV), ejection fraction (EF), peak aortic flow rate (AoF) and the maximum value of the first derivative of the LV pressure curve (dP/d t max) were evaluated in 13 healthy open-chest dogs during triggered AF. All parameters showed a significantly strong positive linear relationship with the ratio of R-R1/R-R2 ( r = 0.65, 0.74, 0.75, and 0.70 for SV, EF, AoF, and dP/d t max, respectively). The calculated value of LV systolic parameters at R-R1/R-R2 = 1 in the linear regression line showed a good relationship and an agreement with the measured average value of the parameter over all cardiac cycles (SV, 12.1 vs. 12.8 ml; EF, 49.6 vs. 51.2%; AoF, 1.37 vs. 1.48 l/min; and dP/d t max, 2,323 vs. 2,454 mmHg/s). Using the LV systolic parameters estimated at R-R1/R-R2= 1 in the linear regression line allows the LV contractile function to be accurately and reproducibly evaluated during AF and obviates the less-reliable process of averaging multiple cardiac cycles.
α1-Adrenoceptor-Gq-RhoA signaling is upregulated to increase myofibrillar Ca2+sensitivity in failing hearts
Authors: Suematsu Nobuhiro , Satoh Shinji , Kinugawa Shintaro , Tsutsui Hiroyuki , Hayashidani Shunji , Nakamura Ryo , Egashira Kensuke , Makino Naoki , Takeshita Akira
Published: December 2017

α1-Adrenergic stimulation, coupled to Gq, has been shown to promote heart failure. However, the role of α1-adrenergic signaling in the regulation of myocardial contractility in failing myocardium is still poorly understood. To investigate this, we observed 1) the effect of phenylephrine on myofibrillar Ca2+sensitivity in α-toxin-skinned cardiomyocytes, and 2) protein expression of Gq, RhoA, and myosin light chain phosphorylation using tachypacing-induced canine failing hearts. Phenylephrine significantly increased myofibrillar Ca2+sensitivity in failing but not in normal cardiomyocytes. Whereas Y-27632 (Rho kinase inhibitor) blocked the phenylephrine-induced Ca2+sensitization in the failing myocytes, calphostin C (protein kinase C inhibitor) had no effect on Ca2+sensitization. The protein expression of Gαqand RhoA and the phosphorylation level of regulatory myosin light chain significantly increased in the failing myocardium. Our results suggest that α1-adrenoceptor-Gqsignaling is upregulated in the failing myocardium to increase the myofibrillar Ca2+sensitivity mainly through the RhoA-Rho kinase pathway rather than through the protein kinase C pathway.
31P NMR quantitation of phosphorus metabolites in rat heart and skeletal muscle in vivo
Authors: Hitchins Sam , Cieslar Julie M. , Dobson Geoffrey P.
Published: December 2017

The aim of this study was to examine two methods of 31P NMR quantitation of phosphocreatine (PCr), ATP, and Pi in rat heart and skeletal muscle in vivo. The first method employed an external standard of phenylphosphonic acid (PPA; 10 mM), and the second method used an enzymatic measurement of tissue ATP equated to the area under the βATP peak. With the use of the external standard, the concentrations of ATP, PCr, and Pi in the rat heart were 4.48 ± 0.33, 9.21 ± 0.65, and 2.25 ± 0.16 μmol/g wet wt, respectively. With the use of the internal ATP standard, measured on the same tissue, the contents (means ± SE) were 4.78 ± 0.19, 9.83 ± 0.18, and 2.51 ± 0.33 μmol/g wet wt, respectively ( n = 7). In skeletal muscle, ATP, PCr, and Pi were 6.09 ± 0.19, 23.44 ± 0.88, and 1.81 ± 0.18 μmol/g wet wt using the PPA standard and 6.03 ± 0.19, 23.30 ± 1.30, and 1.82 ± 0.19 μmol/g wet wt using the internal ATP standard ( n = 6). There was no significant difference for each metabolite as measured by the two methods of quantification in heart or skeletal muscle. The results validate the use of an external reference positioned symmetrically above the coil and imply that each has similar NMR sensitivities (similar signal amplitude per mole of 31P between PPA and tissue phosphorus compounds). We conclude that PCr, ATP, and Pi are nearly 100% visible in the normoxic heart and nonworking skeletal muscle given the errors of measurement.
Tyrosine phosphorylation following alterations in arteriolar intraluminal pressure and wall tension
Authors: Murphy Timothy V. , Spurrell Brian E. , Hill Michael A.
Published: December 2017

Arterioles respond to increased transmural pressure with myogenic constriction. The present study investigated the role of tyrosine phosphorylation in myogenic activity. Cannulated segments of a rat cremaster arteriole were fixed under pressure, followed by incubation with fluorescein isothiocyanate (FITC)-conjugated anti-phosphotyrosine. Smooth muscle cell fluorescence intensity was measured with the use of confocal laser-scanning microscopy. Anti-phosphotyrosine fluorescence intensity in muscle cells of arterioles maintained at 100 mmHg was reduced by the tyrosine kinase inhibitor tyrphostin A47 (30 μM) and increased by the tyrosine phosphatase inhibitor pervanadate (100 μM). In time-course experiments, anti-phosphotyrosine fluorescence increased slowly (over 5 min) after an acute increase in intraluminal pressure, and was dissociated from myogenic contraction (within 1 min). In contrast, angiotensin II (0.1 μM) caused rapid constriction and increased tyrosine phosphorylation. Anti-phosphotyrosine fluorescence was also pressure dependent (10–100 mmHg). Abolition of myogenic activity, either through removal of extracellular Ca2+, or exposure to verapamil (5 μM) or forskolin (0.1 μM) caused a further increase in anti-phosphotyrosine fluorescence. We conclude that transmural pressure and/or wall tension in arterioles causes increased tyrosine phosphorylation; however, this is not involved in the acute phase of myogenic constriction but may be involved in later responses, such as sustained myogenic tone or mechanisms possibly related to growth.
Paraventricular nucleus bicuculline alters frequency components of sympathetic nerve discharge bursts
Authors: Kenney Michael J. , Weiss Mark L. , Patel Kaushik P. , Wang Yan , Fels Richard J.
Published: December 2017

Autospectral and coherence analyses were used to determine the effect of paraventricular nucleus (PVN) GABAA receptor antagonism [microinfusion or microinjections of bicuculline methiodide (BMI) 100 pmoles] on sympathetic nerve discharge (SND) frequency components (bursting pattern and relationships between discharges in regionally selective nerves) in α-chloralose-anesthetized rats. SND was recorded from the renal, splenic, and lumbar nerves. The following observations were made. First, PVN BMI microinjections, but not PVN saline or cortical BMI microinjections, transformed the cardiac-related SND bursting pattern in baroreceptor-innervated rats to one characterized by the presence of low-frequency bursts not synchronized to the cardiac cycle or phrenic nerve discharge bursts. Second, SND pattern changes were similar in the renal, splenic, and lumbar nerves, and peak coherence values relating low-frequency bursts in sympathetic nerve pairs (renal-splenic, renal-lumbar, and splenic-lumbar) were significantly increased from preinjection control after PVN BMI microinjection. Third, PVN BMI microinjections significantly increased the coupling between low-frequency SND bursts in baroreceptor-denervated rats. Finally, PVN BMI-induced changes in the SND bursting pattern were not observed after PVN pretreatment with muscimol (GABA agonist, 1 nmole). We conclude that PVN GABAA receptor antagonism profoundly alters the frequency components in sympathetic nerves.
L-type but not T-type calcium current changes during postnatal development in rabbit sinoatrial node
Authors: Protas Lev , DiFrancesco Dario , Robinson Richard B.
Published: December 2017

Although the neonatal sinus node beats at a faster rate than the adult, when a sodium current ( I Na) present in the newborn is blocked, the spontaneous rate is slower in neonatal myocytes than in adult myocytes. This suggests a possible functional substitution of I Na by another current during development. We used ruptured [T-type calcium current ( I Ca,T)] and perforated [L-type calcium current ( I Ca,L)] patch clamps to study developmental changes in calcium currents in sinus node cells from adult and newborn rabbits. I Ca,T density did not differ with age, and no significant differences were found in the voltage dependence of activation or inactivation. I Ca,L density was lower in the adult than newborn (12.1 ± 1.4 vs. 17.6 ± 2.5 pA/pF, P = 0.049). However, activation and inactivation midpoints were shifted in opposite directions, reducing the potential contribution during late diastolic depolarization in the newborn (activation midpoints −17.3 ± 0.8 and −22.3 ± 1.4 mV in the newborn and adult, respectively, P = 0.001; inactivation midpoints −33.4 ± 1.4 and −28.3 ± 1.7 mV for the newborn and adult, respectively, P = 0.038). Recovery of I Ca,L from inactivation was also slower in the newborn. The results suggest that a smaller but more negatively activating and rapidly recovering I Ca,L in the adult sinus node may contribute to the enhanced impulse initiation at this age in the absence of I Na.
Nitric oxide from perivascular nerves modulates cerebral arterial pH reactivity
Authors: Lindauer Ute , Kunz Alexander , Schuh-Hofer Sigrid , Vogt Johannes , Dreier Jens P. , Dirnagl Ulrich
Published: December 2017

In the isolated rat middle cerebral artery (MCA) we investigated the role of nitric oxide (NO)/cGMP in the vasodilatory response to extraluminal acidosis. Acidosis increased vessel diameter from 140 ± 27 μm (pH 7.4) to 187 ± 30 μm (pH 7.0, P < 0.01). NO synthase (NOS) inhibition by N ω-nitro-l-arginine (l-NNA, 10 μM) reduced baseline diameter (103 ± 20 μm, P < 0.01) and attenuated response to acidosis (9 ± 8 μm). Application of the NO-donors 3-morpholinosydnonimine (1 μM) or S-nitroso- N-acetylpenicillamine (1 μM), or of 8-bromoguanosine 3′,5′-cyclic monophosphate (8-BrcGMP, 100 μM) reestablished pre-l-NNA diameter at pH 7.4 and reversedl-NNA-induced attenuation of the vessel response to acidosis. Restoration of pre-l-NNA diameter (pH 7.4) by papaverine (20 μM) or nimodipine (30 nM) had no effect on the attenuated response to acidosis. Guanylyl cyclase inhibition with 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (5 μM) or NOS-inhibition with 7-nitroindazole (7-NI, 100 μM) reduced baseline vessel diameter (109 ± 8 or 127 ± 11 μm, respectively) and vasodilation to acidosis, and restoration of baseline diameter with 8-BrcGMP (30 μM) completely restored dilation to pH 7.0. Chronic denervation of NOS-containing perivascular nerves in vivo 14 days before artery isolation significantly reduced pH-dependent reactivity in vitro (diameter increase sham: 48 ± 14 μm, denervated: 14 ± 8 μm), and 8-BrcGMP (30 μM) restored dilation to pH 7.0 (denervated: 49 ± 31 μm). Removal of the endothelium did not change vasodilation to acidosis. We conclude that NO, produced by neuronal NOS of perivascular nerves, is a modulator in the pH-dependent vasoreactivity.
Knockout mice heterozygous forSod2show alterations in cardiac mitochondrial function and apoptosis
Authors: Van Remmen Holly , Williams Melissa D. , Guo Zhongmao , Estlack Larry , Yang Hong , Carlson Elaine J. , Epstein Charles J. , Huang Ting Ting , Richardson Arlan
Published: December 2017

Heart mitochondria from heterozygous ( Sod2−/+) knockout mice have a 50% reduction in manganese superoxide dismutase (MnSOD) activity. The decrease in MnSOD activity was associated with increased mitochondrial oxidative damage as demonstrated by a decrease in the activities of iron sulfhydryl proteins sensitive to oxygen stress (aconitase and reduced nicotinamide adenine dinucleotide-oxidoreductase). Mitochondrial function was altered in the Sod2−/+mice, as shown by decreased respiration by complex I and an increase in the sensitivity of the permeability transition to induction by calcium and t-butylhydroperoxide. The increased induction of the permeability transition in heart mitochondria from Sod2−/+.mice was associated with increased release of cytochrome c and an increase in DNA fragmentation. Cardiomyocytes isolated from neonatal Sod2−/+and Sod2−/−mice were more sensitive to cell death than cardiomyocytes from Sod2+/+mice after t-butylhydroperoxide treatment, and this increased sensitivity was prevented by inhibiting the permeability transition with cyclosporin A. These experiments demonstrate that MnSOD may play an important role in the induction of the mitochondrial pathway of apoptosis in the heart, and this appears to occur primarily through the permeability transition.
Endothelium-derived hyperpolarizing factor in coronary microcirculation: responses to arachidonic acid
Authors: Oltman Christine L. , Kane Neal L. , Fudge Jonathon L. , Weintraub Neal L. , Dellsperger Kevin C.
Published: December 2017

In coronary resistance vessels, endothelium-derived hyperpolarizing factor (EDHF) plays an important role in endothelium-dependent vasodilation. EDHF has been proposed to be formed through cytochrome P-450 monooxygenase metabolism of arachidonic acid (AA). Our hypothesis was that AA-induced coronary microvascular dilation is mediated in part through a cytochrome P-450 pathway. The canine coronary microcirculation was studied in vivo (beating heart preparation) and in vitro (isolated microvessels). Nitric oxide synthase (NOS) ( N ω-nitro-l-arginine, 100 μM) and cyclooxygenase (indomethacin, 10 μM) or cytochrome P-450 (clotrimazole, 2 μM) inhibition did not alter AA-induced dilation. However, when a Ca2+-activated K+ channel channel or cytochrome P-450 antagonist was used in combination with NOS and cyclooxygenase inhibitors, AA-induced dilation was attenuated. We also show a negative feedback by NO on NOS-cyclooxygenase-resistant AA-induced dilation. We conclude that AA-induced dilation is attenuated by cytochrome P-450 inhibitors, but only when combined with inhibitors of cyclooxygenase and NOS. Therefore, redundant pathways appear to mediate the AA response in the canine coronary microcirculation.
Transcytosis inhibitorN-ethylmaleimide increases microvascular permeability in rat muscle
Authors: Carlsson Ola , Rosengren Bert-Inge , Rippe Bengt
Published: December 2017

N-ethylmaleimide (NEM) has been claimed to markedly inhibit the transvascular passage of small proteins and albumin by interacting with the docking and fusion of plasmalemmal vesicles with their target membranes. To investigate the role of transcytosis in the transcapillary passage of albumin, we assessed the effects of NEM on125I-labeled radioiodinated serum albumin clearance (RISA-Cl) from blood to muscle in isolated and maximally vasodilated perfused rat hindquarters, in which vascular pressures, pre- and postcapillary resistances, and the capillary filtration coefficient (CFC) were continuously monitored. NEM (0.3–0.5 mM) caused a marked increase mainly in precapillary vascular resistance. Thus the arterial-to-venous resistance ratio in NEM-treated animals was 3.12 ± 0.56 versus 1.66 ± 0.17 during the control period ( P < 0.05). Despite that, there was a doubling of both CFC from 0.0363 ± 0.0028 to 0.0778 ± 0.0101 ml · min−1· mmHg−1· 100 g−1( P < 0.01) and RISA-Cl, compared with the control situation, signaling markedly increased microvascular permeability. Our results strongly suggest that NEM, besides producing marked vasoconstriction, also causes damage to the capillary endothelium. Thus, instead of inhibiting transvascular transport, NEM may induce increases in the bulk transport of albumin from blood to tissue.
Parallel metabotropic pathways in the heart of the toad,Bufo marinus
Authors: Bramich Narelle J. , Cousins Helen M. , Edwards F. R. , Hirst G. D. S.
Published: December 2017

This study examined the transduction pathways activated by epinepherine in the pacemaker region of the toad heart. Recordings of membrane potential, force, and intracellular Ca2+ concentration ([Ca2+]i) were made from arrested toad sinus venosus. Sympathetic nerve stimulation activated non-α-, non-β-adrenoceptors to evoke a membrane depolarization and a transient increase in [Ca2+]i. In contrast, the β-adrenoceptor agonist isoprenaline (10 μM) caused membrane hyperpolarization and decreased [Ca2+]i. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.5 mM) mimicked the isoprenaline-evoked membrane hyperpolarization. Epinephrine (10–50 μM) caused an initial membrane depolarization and an increase in [Ca2+]i followed by membrane hyperpolarization and decreased [Ca2+]i. The membrane depolarizations evoked by sympathetic nerve stimulation or epinephrine were abolished either by the phospholipase C inhibitor U-73122 (20 μM) or by the blocker ofd- myo-inositol 1,4,5,-trisphosphate-induced Ca2+ release, 2-aminoethoxydiphenyl borate (2-APB, 60 μM). Neither U-73122 nor 2-APB had an affect on the membrane hyperpolarization evoked by β-adrenoceptor activation. These results suggest that in the toad sinus venosus, two distinct transduction pathways can be activated by epinephrine to cause an increase in heart rate.
Regulation of ion channels by protein tyrosine phosphorylation
Authors: Davis Michael J. , Wu Xin , Nurkiewicz Timothy R. , Kawasaki Junya , Gui Peichun , Hill Michael A. , Wilson Emily
Published: December 2017

Ion channels are regulated by protein phosphorylation and dephosphorylation of serine, threonine, and tyrosine residues. Evidence for the latter process, tyrosine phosphorylation, has increased substantially since this topic was last reviewed. In this review, we present a comprehensive summary and synthesis of the literature regarding the mechanism and function of ion channel regulation by protein tyrosine kinases and phosphatases. Coverage includes the majority of voltage-gated, ligand-gated, and second messenger-gated channels as well as several types of channels that have not yet been cloned, including store-operated Ca2+channels, nonselective cation channels, and epithelial Na+and Cl−channels. Additionally, we discuss the critical roles that channel-associated scaffolding proteins may play in localizing protein tyrosine kinases and phosphatases to the vicinity of ion channels.
Connexin45 gap junction channels in rat cerebral vascular smooth muscle cells
Authors: Li Xing , Simard J. Marc
Published: December 2017

Cells in blood vessel walls express connexin (Cx)43, Cx40, and Cx37. We recently characterized gap junction channels in rat basilar artery smooth muscle cells and found features attributable not only to these three connexins but also to an unidentified connexin, including strong voltage dependence and single channel conductance of 30–40 pS. Here, we report data consistent with identification of Cx45. Immunofluorescence using anti-human Cx45 and anti-mouse Cx45 antibodies revealed labeling between α-actin-positive cells, and RT-PCR of mRNA from arteries after endothelial destruction yielded amplicons exhibiting 90–98% identity with mouse Cx45 and human Cx45. Dual-perforated patch clamping was performed after exposure to oligopeptides that interfere with docking of Cx43, Cx40, or Cx45. Cell pairs pretreated with blocking peptides for Cx43 and Cx40 exhibited strongly voltage-dependent transjunctional conductances [voltage at which voltage-dependent conductance declines by one-half ( V1/2) = ±18.9 mV] and small single channel conductances (31 pS), consistent with the presence of Cx45, whereas cell pairs pretreated with blocking peptide for Cx45 exhibit weaker voltage-dependent conductances ( V1/2= ±37.9 mV), consistent with block of Cx45. Our data suggest that Cx45 is transcribed, expressed, and forms functional gap junction channels in rat cerebral arterial smooth muscle.
Effect of short-term cyclic stretch on sodium pump activity in aortic smooth muscle cells
Authors: Songu-Mize Emel , Sevieux Nancy , Liu Xiang , Jacobs Mary
Published: December 2017

We previously demonstrated that expression of both the α1- and α2-subunits of Na+-K+-ATPase is elevated after a 2- to 4-day cyclic stretch in aortic smooth muscle cells. In this study, we determined the effect of short-term (2–30 min) cyclic stretch on the activity of the Na pump and investigated possible mechanisms that may be involved in the action of stretch. Na pump activity was significantly increased above the baseline activity between 2 and 30 min of stretch. This effect of stretch was reversible within 1 h. Intracellular Na was also elevated at corresponding time points. Blocking the entry of Na with Gd and amiloride did not affect the stretch-induced increase in Na pump activity. Inhibition of protein kinase A (PKA) activity attenuated the effect of stretch on the Na pump. Furthermore, inhibition of polymerization of actin and phosphatidylinositol 3-kinase (PI3K) activity prevented the action of stretch on Na pump activity. We conclude that the stimulation of the Na pump in response to cyclic stretch requires the integrity of the actin cytoskeleton as well as the activity of PI3K, which has a role in intracellular vesicular trafficking. PKA may also be involved in this effect of stretch on Na pump.
Role of endothelin ETB receptor activation in angiotensin II-induced hypertension: effects of salt intake
Authors: Ballew Jennifer R. , Fink Gregory D.
Published: December 2017

We showed recently that endothelin (ET)A receptors are involved in the salt sensitivity of ANG II-induced hypertension. The objective of this current study was to characterize the role of endothelin ETB receptor activation in the same model. Male rats on fixed normal (2 meq/day) or high (6 meq/day) salt intake received a continuous intravenous infusion of ANG II or salt only for 15 days. During the middle 5 days of the infusion period, rats were given either the selective ETB receptor antagonist A-192621 or the nonselective endothelin receptor antagonist A-182086 (both at 24 mg · kg−1 · day−1intra-arterially). Infusion of ANG II caused a greater rise in arterial pressure in rats on high-salt intake. The administration of A-192621 increased arterial pressure further in all rats. The chronic hypertensive effect of A-192621 was not significantly affected by salt intake or ANG II. The administration of A-182086 lowered arterial pressure chronically only in rats on normal salt intake receiving ANG II. Thus the salt sensitivity of ANG II-induced hypertension is not caused by changes in ETB receptor function.
Diabetes-associated nitration of tyrosine and inactivation of succinyl-CoA:3-oxoacid CoA-transferase
Authors: Turko Illarion V. , Marcondes Sisi , Murad Ferid
Published: December 2017

High levels of reactive species of nitrogen and oxygen in diabetes may cause modifications of proteins. Recently, an increase in protein tyrosine nitration was found in several diabetic tissues. To understand whether protein tyrosine nitration is the cause or the result of the associated diabetic complications, it is essential to identify specific proteins vulnerable to nitration with in vivo models of diabetes. In the present study, we have demonstrated that succinyl-CoA:3-oxoacid CoA-transferase (SCOT; EC 2.8.3.5 ) is susceptible to tyrosine nitration in hearts from streptozotocin-treated rats. After 4 and 8 wk of streptozotocin administration and diabetes progression, SCOT from rat hearts had a 24% and 39% decrease in catalytic activity, respectively. The decrease in SCOT catalytic activity is accompanied by an accumulation of nitrotyrosine in SCOT protein. SCOT is a mitochondrial matrix protein responsible for ketone body utilization. Ketone bodies provide an alternative source of energy during periods of glucose deficiency. Because diabetes results in profound derangements in myocardial substrate utilization, we suggest that SCOT tyrosine nitration is a contributing factor to this impairment in the diabetic heart.
Positive and negative effects of nitric oxide on Ca2+ sparks: influence of β-adrenergic stimulation
Authors: Ziolo Mark T. , Katoh Hideki , Bers Donald M.
Published: December 2017

Nitric oxide (NO) can have a positive or negative effect on cardiac contractility and the ryanodine receptor (RyR). This dual effect has been explained as being dependent on the concentration of NO. We find that cellular RyR response to NO is also dependent on the degree of β-adrenergic stimulation, and thus the state of protein kinase A activation. Ca2+ spark frequency (CaSpF) in rat ventricular myocytes was used as an index of resting RyR activity. CaSpF response to β-adrenergic stimulation was used as an index of protein kinase A activation. High concentration of isoproterenol, a β-adrenergic agonist, caused a large increase in CaSpF; addition of NO (spermine NONOate, 300 μM) then caused a decrease in CaSpF. Low concentration of isoproterenol produced only a slight increase in CaSpF, but the same NO concentration now caused a large increase in CaSpF. A dual effect was also observed in twitch. Thus the net direction of the effects of NO on RyR activity and Ca2+transients (directly or by alteration of sarcoplasmic reticulum Ca2+ load) can be reversed, depending on the ambient level of β-adrenergic activation.
Simulation and prediction of functional block in the presence of structural and ionic heterogeneity
Authors: Sampson Kevin J. , Henriquez Craig S.
Published: December 2017

Inhomogeneities in myocardial structure and action potential duration (APD) lead to dispersion of APD throughout the heart. APD gradients in the range of 20–125 ms/cm have been reported to produce functional block. In this study, a multicellular fiber model was used to examine the effect of structural and ionic inhomogeneities on the likelihood of premature stimuli to produce functional block. With the use of both the Fenton-Karma and Luo-Rudy phase II membrane models, functional block is found to occur in tissue with a maximum gradient <45 ms/cm and depends on the spatial extent. In general, the narrower the extent the larger the magnitude needed for block. A simple relationship for predicting block is presented that only requires information about the conduction velocity (CV) restitution properties of the tissue and the APD gradients. Analysis reveals that the effects of a steep CV restitution slope may be beneficial in overcoming intrinsic cellular heterogeneity for a single premature beat.
ETB receptor-deficient rats exhibit reduced contraction to ET-1 despite an increase in ETA receptors
Authors: Perry Melvin G. , Molero Mariela M. , Giulumian Ararat D. , Katakam Prasad V. G. , Pollock Jennifer S. , Pollock David M. , Fuchs Leslie C.
Published: December 2017

Several disease states, including hypertension, are associated with elevations in plasma endothelin-1 (ET-1) and variable changes in vascular contraction to ET-1. The spotting lethal ( sl) rat carries a deletion of the endothelin-B (ETB) receptor gene that prevents expression of functional ETB receptors, resulting in elevated plasma ET-1. On a normal diet, these rats are normotensive and thus provide an opportunity to study the vascular effects of chronically elevated ET-1 in the absence of hypertension. Studies were performed in rats homozygous for the ETBdeficiency ( sl/ sl; n = 8) and in transgenic rats heterozygous for the ETB deficiency ( sl/+; n = 8). Plasma ET-1 was elevated in sl/ sl rats (3.85 ± 0.55 pg/ml) compared with sl/+ rats (0.31 ± 0.11 pg/ml). Mean arterial blood pressure in conscious unrestrained sl/ sland sl/+ rats was 101 ± 5 and 107 ± 6 mmHg, respectively. Concentration-dependent contractions to ET-1 (10−11–10−8 M) were reduced in mesenteric small arteries (150–250 μm) from sl/ sl rats, as indicated by an ∼10-fold increase in EC50. A selective ETA antagonist, A-127722 (30 nM), abolished contraction to ET-1 in both groups, whereas a selective ETB antagonist had no effect. Also, ETB agonists (IRL-1620 and sarafatoxin 6c) produced neither contraction nor relaxation in either group, indicating that contraction to ET-1 in this vascular segment was exclusively ETAdependent. Despite increased plasma ET-1, protein expression of ETA receptors in membrane protein isolated from mesenteric small arteries was increased in sl/ sl compared with sl/+ rats, as shown by Western blotting. These results indicate that, in ETB-deficient rats, ETA-induced contraction is reduced in vessels normally lacking ETB-mediated effects. Reduced contraction may be related to elevated plasma ET-1 and occurs in the presence of increased ETA receptor protein expression, suggesting an uncoupling of ETA receptor expression from functional activity.
Evidence for stretch-induced resistance increase of proximal coronary microcirculation
Authors: Cornelissen Annemiek J. M. , Spaan Jos A. E. , Dankelman Jenny , Chan Charles C. , Yin Frank C. P.
Published: December 2017

We investigated the influence of stretch on regional hemodynamic parameters of the septal circulation. We used a similar experimental setup and mathematical model, as described previously (14). Five ventricular septa were isolated from anesthetized dogs, sutured to a biaxial stretching apparatus, and perfused with an oxygenated perfluorochemical emulsion at maximal vasodilation. Under unloaded and biaxially stretched conditions, flow and septal thickness (to index vascular volume) were measured continuously. Pressure was varied sinusoidally at 30, 50, and 70 mmHg with amplitude of 7.5 mmHg over frequencies ranging between 0.015 and 7 Hz. Admittance (flow/pressure) and capacitance (thickness/pressure) transfer functions were calculated and interpreted in terms of a two-compartmental model with volume-dependent resistances. Parameter estimation showed that the proximal resistance and compliance were unaffected, whereas the resistance of the proximal part of the microcirculation, including the small arterioles, increased with stretch. The effect of stretch on the distal resistance and capacitance, however, could not be determined unequivocally.
Biventricular systolic function in young lambs subject to chronic systemic right ventricular pressure overload
Authors: Leeuwenburgh Boudewijn P. J. , Helbing Willem A. , Steendijk Paul , Schoof Paul H. , Baan Jan
Published: December 2017

In various clinical situations of congenital heart disease, the right ventricle (RV) is subject to a chronic systemic pressure overload which affects biventricular function and may progress to the development of RV failure. Young lambs (2–3 wk old) underwent adjustable pulmonary artery banding (PAB) at systemic (aortic) level for 8 wk. Biventricular function was determined by using load-independent indexes of global ventricular contractile performance by the end-systolic pressure-volume relationship (ESPVR) using the conductance catheter at baseline and during dobutamine infusion. PAB resulted in a significant fivefold increase in RV end-systolic pressure (12–64 mmHg) and a doubling of the RV-to-left ventricular (LV) wall thickness ratio ( P < 0.01). RV global contractile performance increased significantly, as indicated by an increased slope of the ESPVR. Compared with age-matched control lambs, cardiac output decreased from 2.6 to 1.6 l/min ( P < 0.05) whereas heart rates were equal. In contrast with RV volume, LV volume decreased significantly after PAB ( P < 0.01), whereas the LV-ESPVR slope was unchanged. In the PAB group, the RV, but not the LV, showed a reduced response to dobutamine. We concluded that chronic RV pressure overload for 8 wk results in diminished pump function despite compensatory increased RV global contractile performance.
Agonist-specific differences in mechanisms mediating eNOS-dependent pial arteriolar dilation in rats
Authors: Xu H.-L. , Feinstein D. L. , Santizo R. A. , Koenig H. M. , Pelligrino D. A.
Published: December 2017

Nitric oxide (NO), derived from the endothelial isoform of NO synthase (eNOS), is a vital mediator of cerebral vasodilation. In the present study, we addressed the issue of whether the mechanisms responsible for agonist-induced eNOS activation differ according to the specific receptor being stimulated. Thus we examined whether heat shock protein 90 (HSP90), phosphatidylinositol-3-kinase (PI3K), and tyrosine kinase participate in ACh- versus ADP-induced eNOS activation in cerebral arterioles in vivo. Pial arteriolar diameter changes in anesthetized male rats were measured during sequential applications of ACh and ADP in the absence and presence of the nonselective NOS inhibitor N ω-nitro-l-arginine methyl ester (l-NAME), the neuronal NOS (nNOS)-selective inhibitor ARR-17477, the HSP90 blocker 17-(allylamino)-17-demethoxygeldanamycin (AAG), the PI3K inhibitor wortmannin (Wort), or the tyrosine kinase blocker tyrphostin 47 (T-47). Only NOS inhibition with l-NAME (not ARR-17477) reduced ACh and ADP responses (by 65–75%), which suggests that all of the NO dependence in the vasodilating actions of those agonists derived from eNOS. Suffusions of AAG, Wort, and T-47 were accompanied by substantial reductions in ACh-induced dilations but no changes in the responses to ADP. These findings suggest that muscarinic (ACh) and purinergic (ADP) receptor-mediated eNOS activation in cerebral arterioles involve distinctly different signal transduction pathways.
Blood volume and its relation to peak O2consumption and physical activity in patients with chronic fatigue
Authors: Farquhar William B. , Hunt Brian E. , Taylor J. Andrew , Darling Stephen E. , Freeman Roy
Published: December 2017

Individuals with chronic fatigue syndrome (CFS) experience a number of somatic complaints including severe, disabling fatigue, and exercise intolerance. We hypothesized that hypovolemia, through its interaction with central hemodynamics, would contribute to the exercise intolerance associated with this disorder. We examined blood volume, peak aerobic power, habitual physical activity, fatigue level, and their interrelations to understand the physiological basis of this disorder. Seventeen patients who met the Centers for Disease Control criteria for CFS and 17 age-matched controls participated in the study. Blood volume was assessed using a single bolus injection of Evans blue dye. Peak oxygen consumption was measured during exercise on an upright cycle ergometer. Supine cardiac output and stroke volumes were measured using CO2 rebreathing. Questionnaires were used to assess habitual physical activity and fatigue. Patients displayed a trend for a 9% lower blood volume (58.3 ± 2.1 vs. 64.2 ± 2.5 ml/kg, P = 0.084) and had a 35% lower peak oxygen consumption (22.0 ± 1.2 vs. 33.6 ± 1.9 ml/kg, P < 0.001). These two variables were highly related within the patients ( r = 0.835, P < 0.001) and the controls ( r = 0.850, P < 0.001). Peak ventilation and habitual physical activity were significantly lower in the patients. Fatigue level was not related to any of the measured physiological parameters within the CFS group. In conclusion, individuals with CFS have a significantly lower peak oxygen consumption and an insignificant trend toward lower blood volume compared with controls. These variables were highly related in both subject groups, indicating that blood volume is a strong physiological correlate of peak oxygen consumption in patients with CFS.
Effect of variations of blood flow on renal oxygen extraction
Authors: Levy Matthew N.
Published: December 2017

Temperature gradients have been established in the isolated kidney of the dog in an attempt to ascertain the changes in oxygen extraction of the cortical and medullary regions of the kidney in response to reductions of blood flow. Cooling of the saline bath in which the kidney was immersed resulted in hypothermia of an external zone of cortex. Consequently, the rate of O2 consumption of the medulla plus a zone of juxta-medullary cortex was relatively exaggerated. Cooling the renal arterial blood, on the other hand, rendered the deeper regions hypothermic, and the relative role played by the external zone of cortex was enhanced. Under either set of conditions, reduction of the renal blood flow resulted in only slight changes in O2 extraction which were not significantly different from the behavior of the entire kidney. It is concluded that the superficial and deeper regions of the kidney extract O2 in a similar fashion in response to moderate reductions of blood flow.
Distribution of sulfur-35- and gold-198-labeled gold thioglucose in mice
Authors: Swartz H. A. , Christian J. E. , Andrews F. N.
Published: December 2017

Radioactive gold thioglucose was prepared using gold-198 and sulfur-35. It was administered in normal saline solution to female Rockland Swiss mice between 4 and 5 weeks of age and weighing approximately 20 gm. The labeled compound was given at a dose of 1 mg/gm of body weight and the radioactive dose was 0.2 uc/gm. The distribution of the labeled compound was determined at intervals of 30 minutes, 2, 6, 18 and 48 hours. The hypothalamic levels of radioactivity of mice treated with both sulfur-35- and gold-198-labeled gold thioglucose were significantly greater than those of the hindbrain and cerebrum at all time intervals with the exception of the hindbrain at 30 minutes. Autoradiographs of mice treated with gold-198-labeled material showed a localization of radioactivity in the diencephalon, which contains the hypothalamus. The kidney had the highest concentration of both labeled compounds at 30 minutes, and adrenal values were close to those of the kidney. Lesser degrees of radioactivity were found in the spleen, liver, muscle and blood.
Effect of hypothermia on histamine release induced by epinephrine infusion
Authors: Szilagyi T. , Kover A. , Csaba B.
Published: December 2017

Experiments were performed on dogs anesthetized with chloralose. Epinephrine was infused (20 µg/kg/min.) into the saphenous vein and blood was taken from the femoral artery. Diffusible histamine contents of the plasma were estimated with the superfusion method. It was found that in normothermia epinephrine infusion results in a considerable rise of histamine level. After the cooling of the animals (21.5°–23°C) histamine release does not take place at all during and after the epinephrine infusion, and the histamine content of the blood does not change.