bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic basis of decreased transient outward K+ current in ventricular myocytes from diabetic rats
Authors: Xu Z. , Patel K. P. , Rozanski G. J.
Published: December 2017

The purpose of this study was to examine the mechanisms of alterations in cardiac K+ channel function in early stages of experimental diabetes mellitus induced by streptozotocin. Transient outward (Ito) and inward rectifier (IK1) K+ currents were recorded by the whole cell voltage-clamp technique in ventricular myocytes isolated from hearts of 2- to 4-wk diabetic and age-matched control rats. Ito density in myocytes from diabetic rats was approximately 30% less than control (at +60 mV; P < 0.01) under basal recording conditions in the presence of 18 mM external glucose, whereas IK1 density was not different between groups. When external glucose concentration was decreased to 5 mM for 4-6 h, basal Ito density was not changed in either group of myocytes. To further examine the possible metabolic basis of reduced Ito density in myocytes from diabetic rats, we separately tested three structurally different compounds that affect substrate utilization in cardiac myocytes: insulin (0.1 microM), dichloroacetate (1.5 mM), and L-carnitine (10 mM). Each compound completely normalized Ito density in myocytes from diabetic rats treated in vitro for 4-6 h. The same agents had no effect on Ito density in control myocytes, nor was IK1 altered in either group of cells. These data provide the first evidence to support the hypothesis that there is a metabolic basis for decreased Ito density in diabetic rat ventricular myocytes in early stages of this model. Furthermore, our data suggest that depressed glucose metabolism in the diabetic heart may be a key factor underlying changes in Ito channel function, because agents that increase glucose utilization normalize Ito density within a short time period.
Role of intracellular alkalinization in inhibition of acetylcholine-induced relaxation by FMLP in rat aorta
Authors: Ando K. , Fujita T.
Published: December 2017

N-formylmethionyl-leucyl-phenylalanine (FMLP), a chemotactic tripeptide, is known to cause intracellular alkalinization. Moreover, there is a specific receptor for FMLP in vascular endothelial cells but not in vascular smooth muscle cells. Because we have already reported that intracellular alkalinization inhibits acetylcholine (ACh)-induced relaxation, we examined whether FMLP alters the vasodilation of endothelial cells through intracellular alkalinization. FMLP reduced ACh-induced relaxation in aortic rings from Sprague-Dawley rats but did not affect nitroglycerin-induced relaxation. N-t-butoxycarbonyl-phenylalanyl -D-leucyl-phenylalanyl-D-leucyl-phenylalanine, a specific formyl receptor antagonist, reversed the impairment of ACh-induced relaxation, as did the protein kinase C inhibitors sphingosine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). The sodium/proton antiport inhibitor amiloride and the proton ionophore nigericin normalized the attenuated ACh-induced relaxation. FMLP-induced impairment was normalized by the phospholipase A2 inhibitor quinacrine, the cyclooxygenase inhibitor indomethacin, and the antagonists of the prostaglandin H2 and/or thromboxane A2 receptor, ONO-3708 and S-1452, respectively. Superoxide dismutase inhibited the effect of FMLP. In conclusion, FMLP attenuated ACh-induced relaxation, possibly through intracellular alkalinization. Increased production of vasoconstrictor prostaglandin(s) and superoxide may contribute to the inhibitory effect of FMLP-induced alkalinization on ACh-induced relaxation.
IK of rabbit ventricle is composed of two currents: evidence for IKs
Authors: Salata J. J. , Jurkiewicz N. K. , Jow B. , Folander K. , Guinosso P. J. , Raynor B. , Swanson R. , Fermini B.
Published: December 2017

The delayed rectifier K+ current (IK) in rabbit heart has long been thought to consist of only a single, rapidly activating, dofetilide-sensitive current, IKr. However, we find that IK of rabbit ventricular myocytes actually consists of both rapid and slow components, IKr and IKs, respectively, that can be isolated pharmacologically. Thus, after complete blockade of IKr with dofetilide, the remaining current, IKs, is homogeneous as judged by an envelope of tails test. IKs activates and deactivates slowly, continues to activate during sustained depolarizations, has a half-activation potential of 7.0 +/- 0.8 mV and slope factor of 11.0 +/- 0.7 mV, reverses at -77.2 +/- 1.3 mV (extracellular K+ concentration = 4 mM), is increased by removing extracellular K+, and is enhanced by isoproterenol and stocked by azimilide. Northern analysis demonstrates that the minK (IsK) gene, which encodes a subunit of the channel that underlies the IKs current, is expressed in rabbit heart. Expression of the rabbit protein in Xenopus oocytes elicits a slowly activating, voltage-dependent current, IsK, similar to those expressed previously from mouse, rat, guinea pig, and human genes. The results demonstrate that IKs is present in rabbit ventricle and therefore contributes to cardiac repolarization in this species.
Cellular basis for burn-mediated cardiac dysfunction in adult rabbits
Authors: Horton J. W.
Published: December 2017

We have shown that cutaneous burn injury impairs cardiac contractile performance; however, the mechanisms remain unclear. In this study, New Zealand White rabbits were anesthetized with isoflurane, given a full-thickness scald burn over 30% of total body surface area, and resuscitated with lactated Ringer solution (4 ml.kg-1.%burn-1 for 24 h); rabbits handled in an identical fashion were given a sham burn. Serum obtained from burned and control (sham-burned) rabbits was aliquoted and frozen at -70 degrees C until assay. Polymorphonuclear neutrophils (PMN) were isolated 24 h postburn from both sham and burned rabbits to yield preparations with > 95% PMN with > 95% viability. Cardiac myocytes were isolated by retrograde perfusion of hearts with Ca(2+)-free collagenase-Tyrode buffer, suspended in Krebs-Henseleit buffer containing 10% fetal bovine serum and 1.8 mM Ca2+, and incubated (1 x 10(5) cells/well) in a CO2 incubator under several experimental conditions, including buffer alone, buffer plus 10% burn serum, buffer plus 10% sham serum, or buffer plus either burn or sham PMN (25 x 10(5) cells/well). Myocyte viability (%) and creatine kinase (CK; units.ml-1.10(5) cells-1) were unchanged after incubation with sham plasma or sham PMN. Incubation of sham myocytes with burn plasma caused viability to fall (from 79 +/- 3 to 54 +/- 4%, P < 0.002), whereas CK rose (from 1,639 +/- 115 to 2,803 +/- 132 units.ml-1.10(5) cells-1, P < 0.01). Similarly, incubation of sham myocytes with burn PMN reduced viability (from 83 +/- 2 to 50 +/- 3%, P < 0.01), whereas CK remained unchanged (1,880 +/- 168 units.ml-1.10(5) cells-1). Our data indicate that circulating myocardial depressant factors after burn injury contribute to cardiac myocyte injury.
Comparison of linear and nonlinear formulations of the three-element windkessel model
Authors: Fogliardi R. , Di Donfrancesco M. , Burattini R.
Published: December 2017

The three-element windkessel model incorporating a constant compliance (model A) was compared with two nonlinear versions of the same model (models B1 and B2) incorporating a pressure-dependent compliance. The aim was to test whether nonlinear elasticity yielded better model behavior in describing ascending aortic pressure-flow relationships and interpreting the physical properties of the arterial system. Exponential and bell-shaped compliance vs. pressure curves were assumed in models B1 and B2, respectively. To test these models, we used measurements of ascending aortic pressure and flow from three dogs under a wide variety of hemodynamic states obtained by administering vasoactive drugs and by pacing the heart. These data involved pressure waves with and without an evident oscillation during diastole. Model parameters were estimated by fitting experimental and model-predicted ascending aortic pressures. Our results indicated that only models A and B1 were identifiable. Fits to ascending aortic pressure obtained from model B1 were significantly better than fits obtained from model A. However, 1) the accuracy of parameter estimates, as judged from parameter estimation error analysis, was better in model A than in model B1, 2) the estimates of characteristic parameters of the compliance vs. pressure relation in model B1 were inconsistent with expected physiological trends of this relation, and 3) model B1 did not improve the approximation of diastolic pressure in the presence of an evident oscillation. We conclude that, even in the presence of better data fit, the nonlinear three-element windkessel cannot be preferred over the traditional linear version of this model.
Endothelial vasoconstrictor prostanoids modulate contractions to acetylcholine and ANG II in Ren-2 rats
Authors: Noll G. , Lang M. G. , Tschudi M. R. , Ganten D. , Luscher T. F.
Published: December 2017

We investigated vascular function in mouse Ren-2 transgenic rats with hypertension. Mesenteric resistance arteries of transgenic and Sprague-Dawley rats (controls) were isolated at ages 6 and 12 wk and suspended in myographs for isometric tension recording. Systolic blood pressure was higher in transgenic than control rats (P < 0.05). Contractions to norepinephrine and endothelin-1 were comparable in transgenic and control rats, but the sensitivity decreased with age in both strains (P < 0.05). Contractions to angiotensin I were comparable in 6-wk-old transgenic rats and controls, but the response to angiotensin I was more pronounced in transgenic rats at 12 wk of age. Contractions to angiotensin II were higher in transgenic rats and decreased with age in both strains. Preincubation with the cyclooxygenase inhibitor meclofenamate or the thromboxane receptor antagonist SQ-30741 blunted the response only in 6-wk-old transgenic rats. In quiescent vascular rings, acetylcholine evoked endothelium-dependent contractions after inhibition of nitric oxide formation by N omega-nitro-L-arginine methyl ester only in transgenic rats. These contractions were inhibited by SQ-30741 (P < 0.05) but not by the thromboxane synthase inhibitor CGS-13080. Contractions to the thromboxane analogue U-46619 were comparable in both strains at the age of 6 wk; sensitivity was increased in transgenic rats at 12 wk (P < 0.05). In conclusion, in mesenteric resistance arteries of Ren-2 transgenic rats I) contractions to angiotensin I and II but not to norepinephrine and endothelin-1 are increased, and 2) acetylcholine as well as angiotensin II modulate endothelium-dependent contractions mediated by prostaglandin H2. These alterations together with increased sensitivity to thromboxane could contribute to maintenance as well as to impaired tissue perfusion of this form of hypertension.
Transgenic manipulation of beta-adrenergic receptor kinase modifies cardiac myocyte contraction to norepinephrine
Authors: Korzick D. H. , Xiao R. P. , Ziman B. D. , Koch W. J. , Lefkowitz R. J. , Lakatta E. G.
Published: December 2017

To determine the direct functional significance of the beta-adrenergic receptor (AR) kinase 1 (beta ARK1) on myocardial performance in the absence of tonic sympathoadrenal neural activation and mechanical loading, we measured the contractile responses to acute beta 1-AR stimulation in left ventricular myocytes isolated from nontransgenic control (NTG) and transgenic mice overexpressing either beta ARK1 (TG beta K12) or a beta ARK1 inhibitor (TGMini27). Contractile response to five concentrations (10(-8)-10(-7) M) of the beta 1-AR agonist norepinephrine (NE) plus prazosin (10(-6) M) was measured after a 60-s rest, i.e., rested-state contraction (RSC), and during steady-state contraction (SSC) stimulation at 0.5 Hz (23 degrees C). At baseline, resting cell length was significantly greater in TG beta K12 myocytes (P < 0.05); however, there were no significant differences in RSC or SSC among NTG, TG beta K12, or TG Mini27 mice. On the other hand, both the dose-response curve and kinetics for the NE-induced SSC response normalized to RSC (SSC/RSC) were significantly different among experimental groups (P < 0.001). Specifically, maximal SSC induced by NE in myocytes isolated from TG beta K12 was only 70% of the response observed in NTG cells and 50% of the response measured in TGMini27. These data suggest that 1) in the absence of circulating catecholamines or basal sympathetic tone, beta ARK1 actions in single myocytes are minimal, and 2) substantial functional beta ARK1 modulation of beta 1-AR signaling occurs in cardiac myocytes even during short-term beta 1-AR stimulation. These results are consistent with a role for agonist-induced phosphorylation and desensitization of cardiac beta 1-ARs by beta ARK1 in single myocytes and highlight the potential functional importance of beta ARK1 as a critical determinant of the cardiac beta 1-AR contractile response.
bFGF restores endothelium-dependent responses of hypercholesterolemic rabbit thoracic aorta
Authors: Meurice T. , Bauters C. , Vallet B. , Corseaux D. , van Belle E. , Hamon M. , Dupuis B. , Lablanche J. M. , Bertrand M. E.
Published: December 2017

In animal models, a hypercholesterolemic diet induces areas of deendothelialization and impairs endothelium-dependent vasorelaxation. Angiogenic growth factors increase endothelial cell growth in vivo. This study was thus designed to test the hypothesis that chronic administration of basic fibroblast growth factor (bFGF) in hypercholesterolemic rabbits might restore normal physiological responses to endothelium-dependent agonists. After feeding on a 2% cholesterol diet for 6 wk, 14 New Zealand White rabbits received twice-weekly intravenous boluses of either 2.5 microg bFGF (hypercholesterolemic bFGF group, n = 6) or placebo (hypercholesterolemic control group, n = 8) for 3 wk and were killed for assessment of in vitro vasoreactivity and for histological analysis. Six animals fed with standard rabbit diet were used to assess normal responses. Endothelium-dependent responses to acetylcholine and to the calcium ionophore A-23187 were reduced in the hypercholesterolemic control group compared with normal rabbits. Hypercholesterolemic animals treated with bFGF had significantly better endothelium-dependent responses than hypercholesterolemic rabbits not treated with bFGF. Endothelium-independent responses did not differ significantly among the three groups. A similar degree of plaque formation was observed in control- and bFGF-treated hypercholesterolemic rabbits. These results show that, in this model of atherosclerosis, bFGF has a highly beneficial effect on the functional responses of atherosclerotic vessels and does not have a deleterious effect on the degree of plaque formation.
Non-insulin-dependent diabetes and hyperglycemia impair rat intestinal flow-mediated regulation
Authors: Jin J. S. , Bohlen H. G.
Published: December 2017

Release of nitric oxide from small arteries and larger arterioles of the intestine maintains their dilation and thereby supports mucosal blood flow. This flow-dependent mechanism can be studied by isosmotic replacement of sodium chloride with mannitol over the mucosa to lower mucosal metabolism and blood flow requirements. We tested the hypothesis that flow-mediated regulation is impaired in the non-insulin-dependent Zucker fatty diabetic (ZFD) male rats because of their marginally impaired endothelium-dependent dilation. Furthermore, we determined whether the depressed acetylcholine dilation associated with acute hyperglycemia in normoglycemic Zucker (NZ) rats also impairs flow-mediated regulation. When mannitol replaced sodium chloride over the villi, intestinal blood flow decreased significantly (P < 0.05) less in ZFD (80.9 +/- 6.8% of control) than NZ rats (40.9 +/- 6.4% of control). After 300 mg/dl hyperglycemia for 30 min, normal arterioles had impaired responses to acetylcholine and the resting blood flow and oxygen consumption were suppressed about 60%, which indicate the importance of basal nitric oxide release for intestinal vascular support of metabolism. The evidence of impaired flow-mediated dilation in ZFD and decreased resting blood flow after hyperglycemia in NZ rats demonstrated that both acute and chronic hyperglycemia disturb endothelial regulation of the intestinal vasculature.
Sympathovagal balance of the heart in subjects with spinal cord injury
Authors: Grimm D. R. , De Meersman R. E. , Almenoff P. L. , Spungen A. M. , Bauman W. A.
Published: December 2017

This study investigated the effect of abnormal autonomic cardiovascular function on heart rate variability (HRV) in individuals classified into four groups: complete quadriplegia, incomplete quadriplegia, low paraplegia, and non-spinal cord injury (SCI) controls. Measurements were collected at baseline and during provocative maneuvers. Spectral analysis using a fast-Fourier transform algorithm revealed two spectral components of HRV, termed low frequency (LF) and high frequency (HF); the LF-to-HF ratio (estimate of sympathovagal balance) was also calculated. Each group of subjects with quadriplegia exhibited significantly lower spectral components for both baseline and composite provocative measures compared with the non-SCI controls (P < 0.05). In addition, the group with paraplegia demonstrated significantly lower HF baseline and LF composite levels than controls (P < 0.05). No differences were observed among all groups for the LF-to-HF ratio. This consistency in the LF-to-HF ratio suggests that the two autonomic divisions that regulate the cardiovascular system maintain homeostasis even when one component is severely compromised. This is supported by the additional findings of decreased parasympathetic activity in the two groups with quadriplegia and the absence of significant differences among any of the four groups at rest in either heart rate or blood pressure.
Influence of temperature on oxygen diffusion in hamster retractor muscle
Authors: Bentley T. B. , Pittman R. N.
Published: December 2017

A mathematical analysis by Popel et al. [Am. J. Physiol. 256 (Heart Circ. Physiol. 25): H921-H924, 1989] of in vivo data on arteriolar O2 loss suggested that Krogh's diffusion coefficient (KO2 = alpha x DO2, where DO2 is the O2 diffusion coefficient and alpha is the tissue O2 solubility) in vivo could be an order of magnitude larger than that calculated from DO2 values measured in vitro at 22 degrees C and extrapolated to 37 degrees C. In this study, to eliminate potential extrapolation errors, we used a miniature hyperbaric chamber with 1-2 atm of O2 to maintain tissue oxygenation and allow DO2 measurements directly at 37 degrees C while using a non-steady-state technique. The need for metabolic poisons that had been required by earlier experimental techniques was thereby eliminated. DO2 measured directly at 37 degrees C (2.42 x 10(-5) cm2/s) and the increase with temperature of DO2 between 30 and 41 degrees C (4.61%/degrees C) were unexpectedly higher than the values we found at lower temperatures. Oxygen consumption was also higher than expected at 37 degrees and 40 degrees C. An analysis of the activation energy for DO2 suggests that at higher temperatures there is a change in the diffusion pathway from that existing at lower temperatures, perhaps caused by phase transitions in the lipid membranes.
Effects of Stroop color-word conflict test on the autonomic nervous system responses
Authors: Hoshikawa Y. , Yamamoto Y.
Published: December 2017

The Stroop color-word test (CWT) is a mental stress test involving sensory rejection and has been used as a model of the defense reaction in humans. The present study was designed to investigate effects of CWT on resting cardiac autonomic nervous system activity evaluated by analyses of heart rate (HR) variability (HRV). Eight healthy subjects performed 21 min of CWT after 14 min of resting control followed by 14 min of recovery (RCV). Beat-to-beat R-R intervals (RRI, i.e., HRV), systolic blood pressure (SBP), and instantaneous lung volume were continuously monitored throughout these periods. Steady-state HRV data (10-12 min) for resting control and recovery (12 min) and for 1-11 min (CWT1) and 11-21 min (CWT2) of CWT were analyzed by coarse-graining spectral analysis to break down their total power into harmonic and nonharmonic (fractal) components. The harmonic component was further divided into low (0.0-0.15 Hz, LF)- and high (>0.15 Hz, HF)-frequency components. Cardiac sympathetic (SNS) and parasympathetic (PNS) nervous system activity indicators were evaluated as LF/HF and HF/TP, respectively [LF, HF, and total spectral power (TP) of HRV]. The fractal component had the spectrum of 1/f(beta), and the spectral exponent beta was calculated. RRI decreased and SBP, plasma norepinephrine, and epinephrine concentrations increased significantly (P < 0.05) in response to CWT (CWT1 and CWT2). PNS and SNS indicators did not show any significant (P > 0.05) difference between resting controls and CWT. Whereas the percentage of fractal components in total HRV remained unchanged, beta decreased significantly (P < 0.05) in response to CWT. Transfer magnitudes from SBP to RRI, calculated by cross-spectral analysis, decreased at CWT2. The transfer magnitudes from instantaneous lung volume to RRI were also decreased significantly (P < 0.05) by CWT. It was concluded that although CWT did not affect the SNS indicator of HRV, despite altered HR and vasomotor responses, tonic sympathetic nervous system influence was observed for norepinephrine and epinephrine. In addition, reflex blood pressure (CWT2) and respiratory modulation of HR (CWT1 and CWT2) decreased during CWT. Mental stress altered the fractal nature of HRV (as judged by decreased beta), but mechanism(s) responsible for this change remained unknown.
A new, concise dialysis approach to assessment of cardiac sympathetic nerve terminal abnormalities
Authors: Yamazaki T. , Akiyama T. , Kitagawa H. , Takauchi Y. , Kawada T. , Sunagawa K.
Published: December 2017

We applied a dialysis technique to the hearts of anesthetized cats and examined whether the concentration of dialysate norepinephrine (NE) reflected NE disposition at the cardiac sympathetic nerve terminals. Dialysis probes were implanted in the left ventricular wall, and dialysate NE concentrations were measured as an index of myocardial interstitial NE levels. Stimulation of stellate ganglia significantly increased dialysate NE responses that were suppressed by local administration of an NE-releasing inhibitor (omega-conotoxin GVIA, 10 microM). Increments in basal dialysate NE levels were correlated with concentrations of a locally administered neuronal uptake blocker (desipramine; 1, 10, and 100 microM). Desipramine (100 microM) augmented stimulation-induced dialysate NE responses. Local administration of a neuronal vesicle uptake blocker (reserpine, 1 and 10 microM) did not alter dialysate NE levels but increased dialysate dihydroxyphenylglycol levels. An NE-releasing amine (tyramine, 100 microg/ml) was locally administered to examine NE storage capacity at the nerve terminal. The tyramine-induced NE-releasing response was completely abolished by pretreatment with reserpine (1 mg/kg i.p.). Thus cardiac dialysis with local administration of a pharmacological tool offers a new, concise approach to assessment of neuronal NE release, uptake, vesicle uptake, and storage capacity by cardiac sympathetic nerve terminals.
L-selectin stimulation of canine neutrophil initiates calcium signal secondary to tyrosine kinase activation
Authors: Crockett-Torabi E. , Fantone J. C.
Published: December 2017

Neutrophils play an important role in myocardial ischemia-reperfusion injury. Neutrophil adhesion to the vascular endothelium is one of the important early mechanisms that lead to reperfusion injury. The leukocyte adhesion molecule, L-selectin, plays a major role in the initial interaction between neutrophils and endothelial cells. Intervention aimed at blocking selectins or their associated ligands can exert cardioprotective effects. The purpose of this study was to examine the role of L-selectin in the initiation of transmembrane signaling and regulation of canine neutrophil responses. Cross-linking of canine neutrophil L-selectin using anti-L-selectin antibody induced a rapid and transient increase in intracellular Ca2+ levels and superoxide anion generation that were dependent on the extent of L-selectin cross-linking. The responses were significantly inhibited by the protein tyrosine kinase inhibitor, genistein. The results demonstrate that ligation of canine neutrophil L-selectin is coupled to intracellular signal transduction pathways and the generation of second messengers, which may independently play important regulatory roles in modulating neutrophil-endothelial cell interactions.
Neuronal NO promotes cerebral cortical hyperemia during cortical spreading depression in rabbits
Authors: Colonna D. M. , Meng W. , Deal D. D. , Gowda M. , Busija D. W.
Published: December 2017

Temporary elevations in cortical cerebral blood flow (CBF) accompany cortical spreading depression (CSD) in anesthetized animals. We tested the hypothesis that nitric oxide (NO) is an important promotor of CSD-induced cortical hyperemia in urethan-anesthetized rabbits. CBF was measured at four time points by administration of 15-microm microspheres with the reference withdrawal technique. Intravenous administration of the nonspecific NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine increased mean arterial blood pressure and resting cerebrovascular resistance and attenuated CSD-induced hyperemia. Cortical CBF before intraperitoneal 7-nitroindazole (7-NI), a neuronal NOS inhibitor, was 42 +/- 8 and 124 +/- 19 ml x 100 g(-1) x min(-1) at baseline and during CSD, respectively (P < 0.05 by repeated-measures analysis of variance). After 7-NI administration, mean arterial blood pressure, CBF, and cerebrovascular resistance were unchanged from baseline values; cortical CBF was 38 +/- 4 and 90 +/- 8 ml x 100 g(-1) x min(-1) post-7-NI at rest and during a second CSD, respectively. Similar to N(omega)-nitro-L-arginine, 7-NI decreased the cortical hyperemic response during CSD (P < 0.05 by repeated-measures analysis of variance). We conclude that neuronal NOS promotes the temporary cortical hyperemia observed during CSD.
Properties of three COOH-terminal splice variants of a human cardiac L-type Ca2+-channel alpha1-subunit
Authors: Klockner U. , Mikala G. , Eisfeld J. , Iles D. E. , Strobeck M. , Mershon J. L. , Schwartz A. , Varadi G.
Published: December 2017

There is growing evidence for diversity of cardiac-type (class C) voltage-dependent calcium-channel alpha1-subunits arising from the alternative splicing of a primary transcript. In this study, we show the existence of carboxy-terminal variability in the human cardiac alpha1-gene by genomic cloning. We found that the genomic DNA segment encoding the COOH-terminal tail of the protein is composed of nine invariable and two alternative exons. The alternative utilization of these latter two exons gives rise to the formation of three message variants for this region. Reverse transcription followed by polymerase chain reaction and radioanalytic quantitation of the reverse transcription-polymerase chain reaction products showed significant variations in the distribution of these isoforms (hHt alpha1, rHt alpha1, fHt alpha1) in distinct parts of the heart, the aorta, and fibroblasts. Expression of the three alpha1-isoforms in Xenopus oocytes or in HEK-293 cells and analysis of the kinetics and voltage dependence of the induced calcium-channel currents revealed only insignificant differences in the behavior of these isoforms. When the alpha1-isoforms were coexpressed with a human beta-subunit, no alpha1-specific divergences were observed, but the effects of beta-subunit coexpression on alpha1-isoform biophysical properties were confirmed. The differential abundance of the three isoforms and the influence of an accessory subunit are of potential physiological significance.
Impact of exercise training on ventricular properties in a canine model of congestive heart failure
Authors: Todaka K. , Wang J. , Yi G. H. , Knecht M. , Stennett R. , Packer M. , Burkhoff D.
Published: December 2017

Exercise training improves functional class in patients with chronic heart failure (CHF) via effects on the periphery with no previously documented effect on intrinsic left ventricular (LV) properties. However, because methods used to evaluate in vivo LV function are limited, it is possible that some effects of exercise training on the failing heart have thus far eluded detection. Twelve dogs were instrumented for cardiac pacing and hemodynamic recordings. Hearts were paced rapidly for 4 wk. Six of the dogs received daily treadmill exercise (CHF(EX), 4.4 km/h, 2 h/day) concurrent with rapid pacing, while the other dogs remained sedentary (CHFs). Hemodynamic measurements taken in vivo at the end of 4 wk revealed relative preservation of maximum rate of pressure rise (2,540 +/- 440 vs. 1,720 +/- 300 mmHg/s, P < 0.05) and LV end-diastolic pressure (9 +/- 5 vs. 19 +/- 4 mmHg, P < 0.05) in CHF(EX) compared with CHFs. The hearts were then isolated and cross perfused for in vitro measurement of isovolumic pressure-volume relations; these results were compared with those of six normal dogs (N). Systolic function was similarly depressed in both groups of pacing animals [end-systolic elastance (Ees) values of 1.66 +/- 0.47 in CHFs, 1.77 +/- 0.38 in CHF(EX), and 3.05 +/- 0.81 mmHg/ml in N, with no changes in volume axis interceptors of the end-systolic pressure-volume relationship]. The diastolic myocardial stiffness constant, k, was elevated in CHFs and was normalized by exercise training (32 +/- 3 in CHFs, 21 +/- 3 in CHF(EX), 20 +/- 4 in N). Thus daily exercise training preserved in vivo hemodynamics during 4 wk of rapid cardiac pacing and was accompanied by a significant change in diastolic myocardial stiffness in vitro. These findings suggest that changes in heart function may contribute to the overall beneficial hemodynamic effects of exercise training in CHF by a significant effect on diastolic properties.
Modulation of myogenic responsiveness by CO2 in rat diaphragmatic arterioles: role of the endothelium
Authors: Nagi M. M. , Ward M. E.
Published: December 2017

The effect of hypercapnia on the myogenic response was determined in arterioles (80- to 100-microm internal diameter) isolated from the diaphragms of rats killed by decapitation. All arterioles were exposed to step changes in intraluminal pressure over a range of 10-200 mmHg and had no flow through their lumen. In five separate groups of vessels (n = 7 per group), PCO2 of the superfusing buffer was adjusted to 40, 60, 80, 90, or 100 mmHg. In three further groups of vessels (n = 7 per group), the endothelium was removed by low-pressure air perfusion (2 ml at 20 mmHg) and PCO2 of the superfusing buffer was adjusted to 40, 80, or 100 mmHg. In endothelium-intact vessels, increasing PCO2 to 80 mmHg enhanced the myogenic response, as reflected by a negative slope of the pressure-diameter relationship (slope = -0.164 +/- 0.03 vs. 0.004 +/- 0.02 for vessels at PCO2 = 40 mmHg, P < 0.05). With a PCO2 of 100 mmHg, dilation accompanied increasing intraluminal pressure and the slope of the pressure-diameter curve was positive (0.154 +/- 0.03, P < 0.05 for difference from vessels at PCO2 = 40 mmHg). In deendothelialized vessels, the curve was shifted upward in a parallel manner during exposure to increased PCO2 levels. Moderate hypercapnia (PCO2 < 80 mmHg) elicits endothelium-dependent enhancement of myogenic tone. Severe hypercapnia (PCO2 > 80 mmHg) inhibits myogenic tone through a direct effect on vascular smooth muscle and through endothelium-dependent inhibitory mechanisms.
Modeling pressure-flow relations in cardiac muscle in diastole and systole
Authors: Vis M. A. , Sipkema P. , Westerhof N.
Published: December 2017

Pressure-flow relations were calculated for a symmetrical, maximally dilated, crystalloid-perfused coronary vascular network embedded in cardiac muscle in (static) diastole and (static) systole at two muscle lengths: slack length and 90% of maximal muscle length (Lmax). The calculations are based on the "time-varying elastance concept." That is, the calculations include the mechanical properties of the vascular wall and the (varying) mechanical properties of the myocardial tissue (in cross-fiber direction). We found that, at any given perfusion pressure, coronary flow is smaller in systole than in diastole. Relative reduction in vascular cross-sectional area, which forms the basis of flow impediment, was largest for the smallest arterioles. At a constant perfusion pressure of 62.5 mmHg, the transition from (static) diastole to (static) systole at constant muscle length ("isometric contraction") was calculated to reduce flow by 74% (from 18.9 to 5.0 ml x min(-1) x g(-1)) and by 64% (from 12.6 to 4.6 ml x min(-1) x g(-1)) for the muscle fixed at slack length and 90% of Lmax, respectively. At this perfusion pressure, contraction with 14% shortening (from 90% of Lmax in diastole to slack length in systole) was calculated to reduce flow by 61% (from 12.6 to 5.0 ml x min(-1) x g(-1)). Increasing muscle length from slack length to 90% of Lmax decreases coronary flow by 34% in diastole and by 8% in systole. We conclude that modeling cardiac contraction on the basis of the time-varying elastic properties of the myocardial tissue can explain coronary flow impediment and that contractions, with or without shortening, have a larger effect on coronary flow than changes in muscle length.
Cardiac function in genetically engineered mice with altered adrenergic receptor signaling
Authors: Rockman H. A. , Koch W. J. , Lefkowitz R. J.
Published: December 2017

In disease states such as heart failure, catecholamines released from sympathetic nerve endings and the adrenal medulla play a central role in the adaptive and maladaptive physiological response to altered tissue perfusion. G protein-coupled receptors are importantly involved in myocardial growth and the regulation of contractility. The adrenergic receptors themselves are regulated by a set of specific kinases, termed the G protein-coupled receptor kinases. The study of complex systems in vivo has recently been advanced by the development of transgenic and gene-targeted "knockout" mouse models. Combining transgenic technology with sophisticated physiological measurements of cardiac function is an extremely powerful strategy for studying the regulation of myocardial contractility in normal animals and in models of disease states. The purpose of this review is to summarize current knowledge about the regulation of cardiovascular homeostasis involving signaling pathways through stimulation of adrenergic receptors.
A possible role for L-selectin in the release of polymorphonuclear leukocytes from bone marrow
Authors: van Eeden S. F. , Miyagashima R. , Haley L. , Hogg J. C.
Published: December 2017

Previous studies from our laboratory have shown that the expression of L-selectin on polymorphonuclear leukocytes (PMN) is higher in the bone marrow than in peripheral blood. The present study was designed to determine the location of this L-selectin loss as the PMN pass from the hematopoietic tissue into venous sinusoids of the bone marrow. Bone marrow and peripheral blood samples were collected at the beginning, during, and just after five normothermic cardiopulmonary bypass procedures in which there was active marrow release and compared with five hypothermic procedures in which marrow release was suppressed by lowering body temperature to 27 degrees C. L-selectin expression was measured on PMN in the hematopoietic tissue and venous sinusoids in the bone marrow using quantitative histology and immunocytochemistry. At baseline there was more L-selectin on PMN in the bone marrow hematopoietic tissue than in the sinusoids (24.7 +/- 3.5 vs. 10.3 +/- 2.5%, P < 0.004). Bone marrow release during normothermic cardiopulmonary bypass procedure was associated with a rise in peripheral blood band cells (0.18 +/- 0.7 vs. 2.98 +/- 0.56 x 10(9)/l, P < 0.01) and a further reduction of L-selectin expression on PMN in the sinusoids (P < 0.03). Hypothermia (27 degrees C) prevented both the rise in peripheral blood band cells and the reduction in L-selectin on PMN in the sinusoids. In vitro studies showed that lowering the temperature had a similar effect on shedding of L-selectin from PMN. We conclude that PMN shed L-selectin as they move from the hematopoietic compartment into the venous sinusoids of the bone marrow and postulate that this could control the release of PMN from the marrow.
Ovariectomy eliminates sex differences in rat tail artery response to adrenergic nerve stimulation
Authors: Li Z. , Krause D. N. , Doolen S. , Duckles S. P.
Published: December 2017

The influence of gonadal hormones on vasoconstrictor responses to adrenergic nerve stimulation was investigated by comparing tail arteries from intact and gonadectomized male and female Fisher 344 rats. Arterial ring segments from females were significantly less responsive to transmural nerve stimulation (1-8 Hz) than arteries from age-matched males. Significant male-female differences persisted after correcting the contractile responses for sex-related differences in arterial mass, optimal resting tension, and maximal contractile force. Arteries were taken from cycling, intact females in either proestrus, estrus, metestrus, or diestrus, but no significant differences were found among the four stages for vasoconstrictor responses to either adrenergic nerve stimulation or exogenous norepinephrine. These data suggest adrenergic function in the artery is not affected by hormonal variations during the estrous cycle. After bilateral ovariectomy, however, contractile responses of female arteries to adrenergic nerve stimulation were increased to levels similar to those observed in male arteries. Orchidectomy of males, in contrast, had no effect on neural-evoked contraction. Low concentrations of norepinephrine also produced greater contractile responses in male compared with female arteries; however, this sex-related difference was eliminated by orchidectomy but not ovariectomy. Taken together, the results indicate that circulating gonadal hormones contribute to gender differences observed in rat tail artery. Vasoconstrictor responses to exogenous norepinephrine appear to be enhanced by testicular hormones. In contrast, vasoconstriction induced by adrenergic nerve stimulation appears to be influenced by chronic exposure to circulating ovarian hormones, resulting in a smaller vascular response in female arteries.
Latency of muscle chemoreflex to vascular occlusion of active muscle during dynamic exercise
Authors: Sheriff D. D.
Published: December 2017

When oxygen delivery to active muscle is too low for the ongoing rate of metabolism, metabolites accumulate and activate a muscle chemoreflex that raises arterial pressure. During static muscular contractions, the latency of the onset of increments in sympathetic activity attributed to the muscle chemoreflex is long (1-2 min). This long latency might be caused by slow accumulation of metabolites attributable to low rates of metabolism. Because shortening contractions at a given force per unit time have a much higher energy cost than do static contractions, the muscle chemoreflex should have a much shorter latency during dynamic exercise than during static contractions, and the latency should shorten further with rising exercise intensity. To test these ideas, the latency to the onset of the rise in arterial pressure induced by the muscle chemoreflex following vascular occlusion of active muscle was measured in four dogs exercising on a treadmill. During steady-state exercise of mild to moderate intensity, pressor responses to muscle ischemia were elicited by rapid, complete occlusion of the terminal aorta; this procedure mimics the blockage of muscle blood flow that occurs normally during static contractions. There was a statistically significant effect of exercise intensity on latency (P < 0.001). The latency was 23.5 +/- 4.5, 16.4 +/- 5.6, and 10.1 +/- 2.3 s (means +/- SE) at 3.2 km/h 0% grade, 6.5 km/h 0% grade, and 6.5 km/h 10% grade, respectively. Also, the rate of rise of arterial pressure during chemoreflex activation increased progressively with rising exercise intensity from 0.8 +/- 0.2 mmHg/s during exercise at 3.2 km/h 0% grade to 2.0 +/- 0.5 mmHg/s during exercise at 6.5 km/h 10% grade. Thus the latency of the muscle chemoreflex in response to vascular occlusion during mild dynamic exercise is shorter than has been reported during static contractions of moderate intensity.
Functional implications of myocardial scar structure
Authors: Holmes J. W. , Nunez J. A. , Covell J. W.
Published: December 2017

During healing after myocardial infarction, scar collagen content and stiffness do not correlate. We studied regional mechanics and both area fraction and orientation of large collagen fibers 3 wk after coronary ligation in the pig. During passive inflation of isolated, arrested hearts, the scar tissue demonstrated significantly less circumferential strain but similar longitudinal and radial deformation in comparison with noninfarcted regions of the same hearts. The observed selective resistance to circumferential deformation was consistent with the finding that most of the large collagen fibers in the scar were oriented within 30 degrees of the local circumferential axis. Furthermore, data from a previous study indicate that during ventricular systole these scars resist circumferential stretching, whereas they deform similarly to noninfarcted myocardium in the longitudinal and radial directions. We conclude that large collagen fiber structure is an important determinant of scar mechanical properties and that scar anisotropy allows the scar to resist circumferential stretching while deforming compatibly with adjacent noninfarcted myocardium in the longitudinal and radial directions.
Dynamic vagosympathetic interaction augments heart rate response irrespective of stimulation patterns
Authors: Kawada T. , Sugimachi M. , Shishido T. , Miyano H. , Ikeda Y. , Yoshimura R. , Sato T. , Takaki H. , Alexander J. , Sunagawa K.
Published: December 2017

We previously demonstrated that tonic stimulation of either the sympathetic or the vagal nervous system augmented the dynamic heart rate response to the other of the two systems. We characterized the phenomenon as bidirectional augmentation of heart rate regulation. The question remained unanswered, however, as to whether such augmentation could occur under simultaneous dynamic stimulation of the two systems. The transfer characteristics from nerve stimulation to heart rate were well described by linear systems analysis, although no attention was paid to the aphasic nature of the stimuli in relation to each R-R interval. When we stimulated the two nerves with statistically independent Gaussian white noises, gain of the transfer function increased by 63.2 +/- 47.4% relative to individual stimulation (P < 0.05). When we stimulated the two nerves with mutually reciprocal Gaussian white noises, gain of the transfer function increased by 54.9 +/- 49.1% (P < 0.05). Thus simultaneous dynamic stimulation of the sympathetic and vagal systems bidirectionally augmented heart rate regulation irrespective of the pattern of the stimulation signals.
Biaxial mechanics of the passively overstretched left ventricle
Authors: Emery J. L. , Omens J. H. , McCulloch A. D.
Published: December 2017

Overstretching the intact ventricle increases global compliance as a function of maximum previously experienced load and may have an important role in the diseased heart, but the corresponding changes in local myocardial mechanics and structure are unknown. Therefore, we measured two-dimensional strain on the left ventricular (LV) epicardium in isolated arrested rat hearts sequentially inflated to increasing cavity pressures of 10, 30, and 120 mmHg. Strains at matched LV pressures increased significantly (P < 0.002) as the maximum pressure previously experienced by the LV (Pmax) increased. Compared with Pmax = 10 mmHg, relative increases in fiber strain for Pmax = 30 and 120 mmHg (100 and 149%, respectively) were significantly greater (P < 0.001) than the corresponding increases in cross-fiber (51 and 78%, respectively) and fiber shear (57 and 86%, respectively) strains. Using an optimized prolate spheroidal finite-element model of the rat LV that reliably reproduced experimental strains, we estimated progressive decreases in epicardial biaxial wall stiffness up to 87% with increasing Pmax that were not different in the fiber and cross-fiber directions. Thus, although passive ventricular overloading causes direction-dependent increases in epicardial strain, these changes are the consequence of local myocardial softening that is actually independent of direction.
Involvement of ceramide in inhibitory effect of IL-1 beta on L-type Ca2+ current in adult rat ventricular myocytes
Authors: Schreur K. D. , Liu S.
Published: December 2017

Interleukin (IL)-1 beta has previously been shown to decrease the L-type Ca2+ channel current (ICa,L). Because ceramide has been suggested to mediate many biological effects of IL-1 beta, we examined whether ceramide was involved in the IL-1 beta-induced suppression of ICa,L in adult rat ventricular myocytes. Exposure of myocytes to 5 ng/ml IL-1 beta elicited a 140% increase in ceramide production within 2 min, as measured with 32P phosphorylation. Whole cell patch-clamp techniques were used to measure ICa,L in myocytes internally dialyzed and externally perfused with Na(+)- and K(+)-free solutions. C2 ceramide (1 nM-1 microM), a membrane-permeable analog of ceramide, caused a concentration-dependent inhibition of ICa,L and increased the rate of ICa,L inactivation without altering its gating properties. An inactive ceramide analog failed to inhibit ICa,L. At submaximal concentrations, effects of C2 ceramide and IL-1 beta on ICa,L were additive and saturable. In the presence of a maximally effective concentration of IL-1 beta, C2 ceramide had no further effect on ICa,L. These results suggest that ceramide mediates IL-1 beta-induced suppression of cardiac ICa,L.
New mechanoenergetic evaluation of left ventricular contractility in in situ rat hearts
Authors: Tachibana H. , Takaki M. , Lee S. , Ito H. , Yamaguchi H. , Suga H.
Published: December 2017

We recorded a series of ejecting left ventricular (LV) pressure (P)-volume (V) loops of in situ rat hearts during a gradual ascending aortic occlusion. The end-systolic (ES) P-V relationship (ESPVR) was upward convex curvilinear regardless of LV contractility. The ESPVR was shifted upward in an enhanced contractility by dobutamine and downward in a depressed contractility by propranolol; ESP at a midrange V of 0.1 ml/g LV on each ESPVR increased from 131 +/- 11 to 192 +/- 17 mmHg and decreased from 136 +/- 10 to 110 +/- 7 mmHg, respectively. Furthermore, we obtained an upward concave curvilinear pressure-volume area (PVA; a measure of total mechanical energy)-V (preload) relationship to assess LV work capability in each contractility. This relationship also shifted upward in enhanced contractility and downward in depressed contractility; the PVA at midrange V increased from 7.9 +/- 1.2 to 12.3 +/- 1.5 mmHg. ml.beat-1.g-1 and decreased from 8.2 +/- 0.9 to 6.4 +/- 0.8 mmHg.ml.beat-1.g-1. We conclude that the heights of the ESPVR and PVA-V relationship curves can evaluate LV contractility mechanoenergetically.