Effects Of Β-adrenergic Stimulation Research Articles

Cardiac contractility of the African sharptooth catfish, Clarias gariepinus: role of extracellular Ca2+, sarcoplasmic reticulum, and β-adrenergic stimulation.

This study investigated the dependence of contraction from extracellular Ca2+, the presence of a functional sarcoplasmic reticulum (SR), and the effects of β-adrenergic stimulation using isometric cardiac muscle preparations. Moreover, the expression of Ca2+-handling proteins such as SR-Ca2+-ATPase (SERCA), phospholamban (PLN), and Na+/Ca2+ exchanger (NCX) were also evaluated in the ventricular tissue of adult African sharptooth catfish, Clarias gariepinus, a facultative air-breathing fish. In summary, we observed that (1) contractility was strongly regulated by extracellular Ca2+; (2) inhibition of SR Ca2+-release by application of ryanodine reduced steady-state force production; (3) ventricular myocardium exhibited clear post-rest decay, even in the presence of ryanodine, indicating a decrease in SR Ca2+ content and NCX as the main pathway for Ca2+ extrusion; (4) a positive force-frequency relationship was observed above 60 bpm (1.0 Hz); (5) ventricular tissue was responsive to β-adrenergic stimulation, which caused significant increases in twitch force, kept a linear force-frequency relationship from 12 to 96 bpm (0.2 to Hz), and improved the cardiac pumping capacity (CPC); and (6) African catfish myocardium exhibited similar expression patterns of NCX, SERCA, and PLN, corroborating our findings that both mechanisms for Ca2+ transport across the SR and sarcolemma contribute to Ca2+ activator. In conclusion, this fish species displays great physiological plasticity of E-C coupling, able to improve the ability to maintain cardiac performance under physiological conditions to ecological and/or adverse environmental conditions, such as hypoxic air-breathing activity.

Effects of β-adrenergic stimulation on fetal heart rate, heart rate variability, and T-wave elevation during brief umbilical cord occlusions in fetal sheep.

Circulating catecholamines are critical for fetal adaptation to hypoxia by regulating fetal heart rate (FHR) and promoting myocardial contractility and peripheral vasoconstriction. They have been hypothesized to contribute to changes in FHR variability (FHRV) and T-wave morphology, clinical indexes of fetal well-being during labor. β-Adrenergic blockade with propranolol does not affect FHRV during labor-like hypoxemia and only attenuated the increase in T-wave height between the episodes of hypoxemia. To further investigate the potential role of catecholamines, we investigated whether pharmacological β-adrenergic stimulation could increase FHRV and T-wave elevation during intermittent labor-like hypoxemia. Nineteen chronically instrumented fetal sheep at 0.85 of gestation received isoprenaline hydrochloride (n = 7) or saline (control, n = 12), followed by three 1-min complete umbilical cord occlusions (UCOs) separated by 4-min reperfusion periods. Before the UCOs, infusion of isoprenaline increased FHR (P < 0.001), absolute-T/QRS ratio (P < 0.001), and one measure of FHRV [root-mean-square of successive RR interval differences (RMSSD), P < 0.05]. UCOs triggered deep FHR decelerations. During UCOs, isoprenaline was associated with increased FHR (P < 0.001) and absolute-T/QRS ratio (P < 0.05), but no effect on T/QRS ratio was observed when normalized to baseline before UCOs (normalized-T/QRS ratio). Between UCOs, isoprenaline increased FHR (P < 0.001) and absolute-T/QRS ratio (P < 0.05) but did not affect normalized-T/QRS ratio or any measures of FHRV. Arterial pressure was not affected by isoprenaline at any point. Our findings indicate that circulating catecholamines regulate FHR but not FHRV during labor-like hypoxemia and promote T-wave elevation between but not during intermittent fetal hypoxemia.

P3510Cardiac function and Ca2+-cycling are different according to the level of cardiac-specific FKBP12.6 overexpression

Abstract Cardiac ryanodine receptors (RyR2) have a key role in excitation-contraction coupling by releasing Ca2+ from sarcoplasmic reticulum (SR). In cardiomyocytes, two FK506 binding protein (FKBP) isoforms have been shown to bind and to stabilize RyR2 opening: FKBP12 and FKBP12.6, the later having a stronger affinity for RyR2 despite its lower abundance. Cardiac-specific FKBP12.6 overexpressing mice have fewer arrhythmias induced by β-adrenergic stimulation than wild type (WT) mice, suggesting an implication of FKBP12.6 in an antiarrhythmic mechanism. Heart failure (HF) syndrome has a high incidence of arrhythmias, which may be explained by a decrease of FKBP isoform expression. The precise mechanism of the antiarrhythmic effect of FKBP12.6 overexpression remains unknown. To gain insight into this mechanism, we developed 2 transgenic mouse lines with cardiac-specific moderate- (TG1) and high- (TG2) FKBP12.6 overexpression levels. We characterized cardiac function, [Ca2+]i cycling and its response to β-adrenergic stimulation in both mouse lines. TG1 and TG2 mice developed mild and marked cardiac hypertrophy, respectively, associated with basal cardiac function increase in TG1 mice only. In stimulated cardiomyocytes, [Ca2+]i transient amplitude, measured by confocal microscopy, was higher in TG1 than in WT mice, without a significant difference in their SR Ca2+ content. The effect of β-adrenergic stimulation (50 nM isoproterenol) was attenuated in TG1 mice compared to WT mice, in association with the prevention of pro-arrhythmogenic Ca2+ release events, such as Ca2+ waves. In contrast, TG2 mice showed [Ca2+]i handling characteristics similar to HF, with slower [Ca2+]i transient relaxation. Interestingly, and contrary to HF, pro-arrhythmogenic Ca2+ release events were also reduced in TG2. These results indicate that the level of FKBP12.6 overexpression has distinct effects on cardiac function and on Ca2+-cycling and its response to β-adrenergic stimulation.

Influence of distinct cardiac-specific FKBP12.6 overexpression levels on cardiac function and [Ca2+]i cycling

Cardiac ryanodine receptors (RyR2) have a key role in excitation-contraction coupling by releasing Ca 2+ from sarcoplasmic reticulum (SR). In cardiomyocytes, 2 FK506 binding protein (FKBP) isoforms have been shown to bind and to stabilize RyR2 opening: FKBP12 and FKBP12.6, the later having a stronger affinity for RyR2 despite its lower abundance. Cardiac-specific FKBP12.6 overexpressing mice have fewer arrhythmias induced by β-adrenergic stimulation than wild type (WT) mice, suggesting an implication of FKBP12.6 in an antiarrhythmic mechanism. Heart failure (HF) syndrome has a high incidence of arrhythmias, which may be explained by a decrease of FKBP isoform expression. The precise mechanism of the antiarrhythmic effect of FKBP12.6 overexpression remains unknown. To gain insight into this mechanism, we developed 2 transgenic mouse lines with cardiac-specific moderate- (TG1) and high- (TG2) FKBP12.6 overexpression levels. We characterized cardiac function, [Ca 2+ ]i cycling and its response to β-adrenergic stimulation in both mouse lines. TG1 and TG2 mice developed mild and marked cardiac hypertrophy, respectively, associated with basal cardiac function increase in TG1 mice only. In stimulated cardiomyocytes, [Ca 2+ ]i transient amplitude, measured by confocal microscopy, was higher in TG1 than in WT mice, without a significant difference in their SR Ca 2+ content. The effect of β-adrenergic stimulation (50nM isoproterenol) was attenuated in TG1 mice compared to WT mice, in association with the prevention of pro-arrhythmogenic Ca 2+ release events, such as Ca 2+ waves. In contrast, TG2 mice showed [Ca 2+ ]i handling characteristics similar to HF, with slower [Ca 2+ ]i transient relaxation. Interestingly, and contrary to HF, pro-arrhythmogenic Ca 2+ release events were also reduced in TG2. These results indicate that the level of FKBP12.6 overexpression has distinct effects on cardiac function and on Ca 2+ cycling and its response to β-adrenergic stimulation.

The role of interleukin-6 in intracellular signal transduction after chronic β-adrenergic stimulation in mouse myocardium.

IntroductionInflammatory mediators play an important role in development and progression of cardiovascular disease. Both adrenergic stimulation and high levels of interleukin-6 (IL-6) indicate an unfavorable outcome in patients with myocardial infarction or heart failure. Understanding the interaction between β-adrenergic stimulation and IL-6 in the myocardium may contribute to developing more effective treatments. The aim of this study was to verify the role of IL-6 in the effects of β-adrenergic stimulation in activating selected intracellular signaling pathways in mouse myocardium.Material and methodsExperiments were performed on 12-week-old male mice: 16 C57BL/6JIL6‑/‑TMKopf (IL-6 KO) and 17 C57BL/6J (WT). Animals received intraperitoneal injections of isoproterenol (ISO, 50 mg/kg) or placebo (0.9% NaCl) once a day for 16 days. The phosphorylation of STAT3 (signal transducer and activator of transcription 3), ERK1/2 (extracellular-regulated kinases 1/2), Akt1/2/3, p-38, c-Raf and expression of SOCS3 (suppressor of cytokine signaling 3), PIAS1/3 (protein inhibitors of activated STAT) was assessed by western blotting in the myocardium 24 h after the last injection. Evaluation of gene expression downstream of these pathways was performed by real-time PCR.ResultsChronic ISO treatment leads to increased fibrosis of the myocardium in mice lacking IL-6, which is accompanied by increased activity of ERK1/2, p38 and reduced expression of SOCS3. Administration of ISO in IL-6 KO animals intensified gene expression of proteins activated by MAPK/ERK (myc; CEBPB; BMP4; Fasn; Tank), while it reduced expression of genes repressed by ERK 1/2 (Wisp1, Wnt1).ConclusionsIL-6 plays an important role in regulating the activation of MAPK pathways in the mouse myocardium in response to chronic β-adrenergic stimulation.

HCN as a Mediator of Urinary Homeostasis: Age-Associated Changes in Expression and Function in Adrenergic Detrusor Relaxation

The Hyperpolarization activated, cyclic nucleotide gated (HCN) channel is a candidate mediator of neuroendocrine influence over detrusor tonus during filling. In other tissues, HCN loss with aging is linked to declines in rhythmicity and function. We hypothesized that HCN has an age-sensitive expression profile and functional role in adrenergic bladder relaxation. HCN was examined in bladders from young (2-6 months) and old (18-24 months) C57BL/6 female mice, using qRT-PCR, RNAScope, and Western blots. Isometric tension studies were conducted using bladder strips from young wild-type (YWT), old wild-type (OWT), and young HCN1 knock-out (YKO) female mice to test the role HCN in effects of β-adrenergic stimulation. Hcn1 is the dominant HCN isoform RNA in the mouse bladder wall, and is diminished with age. Location of Hcn RNA within the mouse bladder wall is isoform-specific, with HCN1 limited to the detrusor layer. Passively-tensioned YWT bladder strips are relaxed by isoproterenol in the presence of HCN function, where OWT strips are relaxed only in the presence of HCN blockade. HCN has an age-specific expression and function in adrenergic detrusor relaxation in mouse bladder strips.

A Novel Effect of β-Adrenergic Receptor on Mammary Branching Morphogenesis and its Possible Implications in Breast Cancer.

Understanding the mechanisms that govern normal mammary gland development is crucial to the comprehension of breast cancer etiology. β-adrenergic receptors (β-AR) are targets of endogenous catecholamines such as epinephrine that have gained importance in the context of cancer biology. Differences in β2-AR expression levels may be responsible for the effects of epinephrine on tumor vs non-tumorigenic breast cell lines, the latter expressing higher levels of β2-AR. To study regulation of the breast cell phenotype by β2-AR, we over-expressed β2-AR in MCF-7 breast cancer cells and knocked-down the receptor in non-tumorigenic MCF-10A breast cells. In MCF-10A cells having knocked-down β2-AR, epinephrine increased cell proliferation and migration, similar to the response by tumor cells. In contrast, in MCF-7 cells overexpressing the β2-AR, epinephrine decreased cell proliferation and migration and increased adhesion, mimicking the response of the non-tumorigenic MCF-10A cells, thus underscoring that β2-AR expression level is a key player in cell behavior. β-adrenergic stimulation with isoproterenol induced differentiation of breast cells growing in 3-dimension cell culture, and also the branching of murine mammary epithelium in vivo. Branching induced by isoproterenol was abolished in fulvestrant or tamoxifen-treated mice, demonstrating that the effect of β-adrenergic stimulation on branching is dependent on the estrogen receptor (ER). An ER-independent effect of isoproterenol on lumen architecture was nonetheless found. Isoproterenol significantly increased the expression of ERα, Ephrine-B1 and fibroblast growth factors in the mammary glands of mice, and in MCF-10A cells. In a poorly differentiated murine ductal carcinoma, isoproterenol also decreased tumor growth and induced tumor differentiation. This study highlights that catecholamines, through β-AR activation, seem to be involved in mammary gland development, inducing mature duct formation. Additionally, this differentiating effect could be resourceful in a breast tumor context.

Circulation Research “In This Issue” Anthology

<i>Circulation Research</i> “In This Issue” Anthology

P134Increased beta-adrenergic inotropy in ventricular myocardium from Trpm4 knockout mice

TRPM4 have an extensive role in regulating intracellular calcium dependent cell functions in many cells including mast cells, chromaffin cells and recently in neurons. TRPM4 proteins constitute calcium activated, but calcium impermeable, non-selective cation channels and are expressed both in atrial and ventricular cardiomyocytes. The Trpm4 gene has recently been associated with several disorders, including cardiac conduction diseases such as Progressive Familial Heart Block Type 1, Right Bundle Branch Block and Brugada Syndrome. The physiological function of TRPM4 in the heart remains however incompletely understood. The objective of this study was to establish the role of TRPM4 in left ventricular muscle function. We used TRPM4 knockout mice and performed patch-clamp experiments, membrane potential measurements, microfluorometry, contractility measurements and in vivo pressure-volume loop analysis. We demonstrate that TRPM4 proteins are functionally present in mouse ventricular myocytes and are activated upon calcium induced calcium release. Measurements of action potential duration show that TRPM4 is active during the repolarization of the ventricular action potential. We show a significantly decreased time for 50 % and 90 % repolarization in Trpm4 knockout ventricular myocytes. We also provide evidence that this change in action potential shape leads to an increased driving force for the L-type calcium current during the action potential. Moreover, in vivo pressure-volume analysis and in vitro contraction strength measurement on isolated papillary muscles displays an increased β-adrenergic inotropic response in TRPM4 knockout mice. Taking together these data, our results show that functional TRPM4 proteins are novel determinants of the inotropic effect of β-adrenergic stimulation on the ventricular heart muscle.

In This Issue

HomeCirculation ResearchVol. 112, No. 3In This Issue Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBIn This Issue Originally published1 Feb 2013https://doi.org/10.1161/RES.0b013e318287730bCirculation Research. 2013;112:407β-Adrenergic Signaling and CPC Function (p 476)Download figureDownload PowerPointβ-Adrenergic stimulation of cardiac progenitor cells is a double-edged sword, say Khan et al.During heart failure, β-adrenergic stimulation of the heart is increased to aid in contraction, providing temporary relief to weakened heart muscles. In the long-term however, this stimulation causes cardiac myocytes to die. To prevent this damage β-adrenergic blockers are often used to treat heart failure patients. When cardiac myocytes die, they are replaced, albeit slowly, by cardiac progenitor cells. However, it is unclear how exactly these progenitors are affected by β-blockers, or indeed, by β-adrenergic stimulation. Now, Khan et al report that β-adrenergic stimulation induces mouse cardiac progenitor cells to proliferate. But, just like adult cardiac myocytes, the progenitor cells underwent apoptosis as soon as they were induced to differentiate. The investigators found that progenitor cells expressed only one type of β-adrenergic receptor, β1-AR, but upon differentiation, they started to express a second, β2-AR—also found in mature cardiac myocytes. And because these 2 receptors convey separate effects, the authors suggest that a bipartite approach, involving β1-AR activation and β2-AR blockade, could be more effective in treating heart failure.Pro- and Anti-Apoptotic Signaling of cAMP (p 498)Download figureDownload PowerPointZhang et al suggest replacing β-blockers with a PKA inhibitor to treat heart failure.Much like Khan and colleagues, Zhang et al were interested in the effects of β-adrenergic stimulation and β-blockers on the heart. They knew that long-term β-adrenergic stimulationduring heart failure causes heart cells to die. They also knew that β-blockers prevent this cell death. However, the molecular details of these processes were unclear. β-Adrenergic–induced cell death is thought to be mediated by the stimulation of protein kinase A (PKA), but the effects of β-adrenergic stimulation could also be PKA-independent. To differentiate between PKA and non-PKA effects, the team created transgenic mice expressing a PKA inhibitor. They found that β-adrenergic stimulation in these mice prevented cardiac myocyte death and that the level of protection offered by PKA inhibition was similar to that provided by β-blockers. There was one important distinction, however. The hearts of the transgenic mice when stimulated also exhibited marked ERK activation, which offered further protection to cardiac myocytes. Following myocardial infarction, these PKA-inhibited mice also showed greater improvement in cardiac function than wild-type mice treated with β-blockers. The authors suggest that for treating heart failure patients, PKA-inhibitors may be more effective than β-blockers.Remodeling of Diabetic Bone Marrow (p 510)Download figureDownload PowerPointVascular problems beget more vascular problems in the bone marrow of patients with diabetes, report Spinetti et al.Cardiovascular complications, such as atherosclerosis and capillary damage are common in diabetes and can have far reaching clinical consequences. In mouse models such capillary damage can affect even the bone marrow. Worse still, in the bone marrow, the failing microvasculature, which feeds the stem cell niche, could reduce the production of progenitors, including pro-angiogenic cells. While it has been shown that circulating progenitor cell levels are suppressed in people with diabetes it is unclear whether, like mice, human bone marrow microvasculature is also affected. Spinetti et al show that bone specimens from diabetes patients do indeed exhibit decreased capillary densities and also contain fewer progenitor cells. The team found that while impaired blood supply did contribute to the reduction in progenitor cell populations, high glucose itself also caused these cells to upregulate a pro-apoptosis pathway. This involved inactivation of microRNA miR-155, and the upregulation of its target - the transcription factor, FOXO3a. Taken together, the data suggest that specific treatments designed to preserve the integrity of capillaries of the bone marrow and the function of progenitor cells could prove important for managing diabetes. Previous Back to top Next FiguresReferencesRelatedDetails February 1, 2013Vol 112, Issue 3 Advertisement Article InformationMetrics © 2013 American Heart Association, Inc.https://doi.org/10.1161/RES.0b013e318287730b Originally publishedFebruary 1, 2013 PDF download Advertisement

FKBP12.6 overexpression does not protect against remodelling after myocardial infarction

Reducing the open probability of the ryanodine receptor (RyR) has been proposed to have beneficial effects in heart failure. We investigated whether conditional FKBP12.6 overexpression at the time of myocardial infarction (MI) could improve cardiac remodelling and cell Ca(2+) handling. Wild-type (WT) mice and mice overexpressing FKBP12.6 (Tg) were studied on average 7.5 ± 0.2 weeks after MI and compared with sham-operated mice for in vivo, myocyte function and remodelling. At baseline, unloaded cell shortening in Tg was not different from WT. The [Ca(2+)](i) transient amplitude was similar, but sarcoplasmic reticulum (SR) Ca(2+) content was larger in Tg, suggesting reduced fractional release. Spontaneous spark frequency was similar despite the increased SR Ca(2+) content, consistent with a reduced RyR channel open probability in Tg. After MI, left ventricular dilatation and myocyte hypertrophy were present in both groups, but more pronounced in Tg. Cell shortening amplitude was unchanged with MI in WT, but increased with MI in Tg. The amplitude of the [Ca(2+)](i) transient was not affected by MI in either genotype, but time to peak was increased; this was most pronounced in Tg. The SR Ca(2+) content and Na(+)- Ca(2+) exchanger function were not affected by MI. Spontaneous spark frequency was increased significantly after MI in Tg, and larger than in WT (at 4 Hz, 2.6 ± 0.4 sparks (100 μm)(-1) s(-1) in Tg MI versus 1.6 ± 0.2 sparks (100 μm)(-1) s(-1) in WT MI; P < 0.05). We conclude that FKPB12.6 overexpression can effectively reduce RyR open probability with maintained cardiomyocyte contraction. However, this approach appears insufficient to prevent and reduce post-MI remodelling, indicating that additional pathways may need to be targeted.

Abstract C62: Triiodothyronine (T3) supplementation prevents the overexpresion of invasion factors induced by β-adrenergic stimulation in prostate cancer models

Abstract There are multiple pieces of evidence that the sympathetic nervous system and thyroid hormones play crucial roles in normal and cancerous development of tissues. It is well established that chronic β-adrenergic stimulation (cAMP-PKA-CREB pathway) is a risk factor for progression of prostate cancer because it promotes cell migration, tumor invasion, and metastasis. Moreover, studies in human prostate cancer cells (LNCaP) show that a high dose of adrenaline induces transdifferentiation of secretor epithelium into a neuroendocrine phenotype with high invasive potential. Although studies from our group have shown a direct relation between sympathetic-input and prostate T3 generation (which seems to be associated with epithelial differentiation that occurs at puberty), there is no evidence about T3 effects on the progression of prostate cancer. Studies in hepatic cancer show that T3 administration reverses the neoplastic lesions induced by a chemical carcinogen (differentiating effects). The aim of this study was to analyze, in models of prostate cancer (in vivo and in vitro), the effects of β-adrenergic stimulation, T3, or both on tumor progression. Nude mice (nu/nu, 8 weeks old) were subcutaneously transplanted with human prostate cancer cells (LNCaP). Two days later, the mice were implanted in the back with a controlled-release pellet of isoproterenol (ISO, β-adrenergic agonist, 200 μg/day), and T3 was administrated in the drinking water (2.5 μg/day). Single (ISO or T3) or combined treatments (ISO+T3) were maintained for 6 weeks, and body weight, tumor incidence, and tumor volume were registered every week. In prostate tumor, qRT-PCR was used to analyze the expression of genes related to angiogenesis (vascular endothelial growth factor, VEGF), invasion (urokinase plasmin activator, uPA; metalloproteinase 9, MMP9), and neuroendocrine phenotype (chromogranin A, CgA). The results showed that none of the treatments affected body weight. In the ISO and ISO + T3 groups, tumors appeared in week 3, while in control and T3 groups the onset of the tumors occurred by week 5. In comparison with the control group, ISO treatment decreased tumor growth, but increased the expression of VEGF, uPA, MMP9, and CgA (2-3 fold). These effects are consistent with the well known effects of β-adrenergic stimulation on the acquisition of the neuroendocrine phenotype (slowly proliferating but highly invasive tumors). T3 administration prevents the increase of VEGF, uPA, MMP9, and CgA expression induced by ISO. Administration of T3 alone did not modify the tumoral growth or gene expression mentioned above. Migration assays in vitro of LNCaP cells showed that ISO increased cell migration, and T3 prevented the ISO effect (ISO + T3). These findings suggest that T3 might inhibit the transcription of genes dependent on β-adrenergic stimulation in prostate cancer. Current studies are analyzing if the protective effects of T3 might be associated with CREB inactivation. The authors are grateful to Guadalupe Delgado, Felipe Ortiz, and Martín García for their technical assistance. We thank Dr. Erika Rendón (Facultad de Medicina, UNAM) for her advice for the in vitro assays. Supported by CONACYT (78955, 87196, 127368), PAPIIT (IN201210). Citation Format: Evangelina Delgado-González, Carmen Aceves, Brenda Anguiano. Triiodothyronine (T3) supplementation prevents the overexpresion of invasion factors induced by β-adrenergic stimulation in prostate cancer models [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C62.

Effect of β-adrenergic stimulation on QT interval accommodation

QT interval correction formulas are based on instantaneous heart rate (HR), but QT interval adaptation to sudden HR change occurs gradually. In humans, the QT interval has been reported to reach a new steady-state value in about 2 minutes. This study sought to assess β-adrenergic stimulation effects on QT interval response to HR change. Ten subjects (42.1 ± 15.3 years, 3 men) undergoing radiofrequency ablation of supraventricular tachycardia were studied. Atrial pacing for 5 minutes at an HR ranging from 60 to 140 beats/min was performed before and during dobutamine infusion (10 μg/kg/min). The QT response to sudden HR change was evaluated. The QT response to sudden HR change consists of an immediate response (IR), followed by a gradual monoexponential course to the new steady-state value. Linear function results in inferior fit of QT adaptation course (P < .05 compared with exponential). The time constant of the exponential is approximately 1 minute (50.9 ± 11.4 seconds). The IR magnitude is approximately 3% of the RR interval change (2.97% ± 2.01%). Dobutamine shortens steady-state QT at given HR (from 301.8 ± 11.2 ms to 290.6 ± 13.2 ms at 120 beats/min; P < .001) and increases IR magnitude (to 13.28% ± 8.99% of RR change; P < .01). During sinus rhythm, QT variability and QT variability index were significantly increased by dobutamine. QT adaptation has 2 distinct phases, which might have different mechanisms. The effect of β-adrenergic stimulation on IR may increase QT variability by increasing the immediate response to HR variability. These results may be important in the assessment of drug effects on repolarization and for understanding of QT variability.

Stress synchronizes calcium release and promotes SR calcium leak

Stress synchronizes calcium release and promotes SR calcium leak

Sudden Cardiac Death

Sudden cardiac death is often due to a ventricular arrhythmia. When a patient presents with a malignant arrhythmia unrelated to a transient reversible cause, there is a high probability of recurrent arrhythmia and sudden death. Clinical trials have shown a uniform survival benefit from implantable cardioverter-defibrillator (ICD) therapy in survivors of a malignant arrhythmia when compared with drug therapy. However, only 1% to 5% of patients survive an out-of-hospital cardiac arrest, emphasizing the need for primary prevention of sudden death. Clinical trial data available in this regard are largely limited to patients with coronary artery disease (CAD). Mortality can be reduced by the ICD in patients with CAD and depressed left ventricular ejection fraction (LVEF) less than 30%. If left ventricular function is only moderately depressed (LVEF between 30% and 40%), the presence of nonsustained ventricular tachycardia with inducible ventricular arrhythmia at electrophysiologic testing identifies patients who benefit from an ICD. The role of the ICD in primary prevention of sudden death in patients with nonischemic dilated cardiomyopathy is less clear at this time. Preliminary data indicate that the presence of heart failure symptoms in this population increases risk of sudden death that can be prevented by an ICD. Antiarrhythmic drugs have little role in prevention of sudden death; however, drugs that block the effects of β-adrenergic stimulation, angiotensin, and aldosterone reduce mortality partly through their salutary effects on sudden death. Finally, a number of inherited defects of genes coding for ion channels, contractile sarcomeric proteins, and cell-to-cell junction proteins can result in primary electrical abnormalities and sudden death. The ICD is effective for secondary prevention, but its role in primary prevention is controversial and should be based on individual risk factors.

Correlation Of Levels And Time Course Of Intracellular And Mitochondrial Calcium Signals In Isolated Adult Cardiac Cells

The contribution of mitochondria to Ca2+ homeostasis in the adult cardiac myocyte is uncertain. We have successfully targeted a genetically encoded Ca2+ sensitive inverse pericam to the mitochondria of primary mammalian ventricular cardiomyocytes by adenoviral mediated expression (AdMitycam). Cytoplasmic Ca2+ ([Ca2+]cyt) and mitochondrial Ca2+ ([Ca2+]mit) were monitored simultaneously in adult rabbit cardiomyocytes by loading AdMityCam expressing cells with Fura2. [Ca2+]cyt and [Ca2+]mit were recorded during voltage clamp stimulation (0.5Hz). The sarcoplasmic reticulum (SR) was loaded at a range of [Ca2+] by increasing [Ca2+]0 (1.8-7.2mM) and by β-adrenergic stimulation (500nM isoproterenol). Beat-to-beat Ca2+ transients were observed in both [Ca2+]cyt and [Ca2+]mit. The relationship between mean [Ca2+]cyt and [Ca2+]mit was unity at [Ca2+] below ∼133nM, above this value [Ca2+]mit>[Ca2+]cyt. Under conditions of spontaneity [Ca2+]mit>[Ca2+]cyt (204±54.0nM vs. 118±26.7nM respectively). In electrically stimulated events the kinetics of the [Ca2+]mit transient upstroke (time-to-peak (TTP)) was significantly slower than cytoplasmic. [Ca2+]mit TTP decreased with increasing SR Ca2+ load whilst [Ca2+]cyt TTP increased. The time to 50% decay of the [Ca2+]mit in these electrically stimulated events however was significantly faster than cytoplasmic. β-adrenergic stimulation further decreased the TT50% decay of the [Ca2+]cyt by ∼25% and [Ca2+]mit by ∼60%. The mechanism behind the effects of isoproterenol on the kinetics of the mitochondrial Ca2+ signal is unknown but may be linked to known effects of β-adrenergic stimulation on Mg2+ extrusion. Whilst the kinetics of the electrically triggered [Ca2+]cyt and [Ca2+]mit events differed, the changes in [Ca2+]cyt and [Ca2+]mit during spontaneous SR Ca2+ release events were similar in time course. These data suggest that Ca2+ accumulation by cardiac mitochondria depends on the time course and magnitude of the cytoplasmic Ca2+ signal and the presence of β-adrenergic stimulation.

Effects of β-adrenergic stimulation on L-type Ca2+ currents in rabbit ventricular myocytes during administration of volatile anesthetics

Effects of β-adrenergic stimulation on L-type Ca2+ currents in rabbit ventricular myocytes during administration of volatile anesthetics

Endocrine Role of the Renin-Angiotensin System in Human Adipose Tissue and Muscle

The renin-angiotensin system has been implicated in obesity-related hypertension and insulin resistance. We examined whether locally produced components of the renin-angiotensin system in adipose tissue and skeletal muscle play an endocrine role in vivo in humans. Furthermore, the effects of beta-adrenergic stimulation on plasma concentrations and tissue release of renin-angiotensin system components were investigated. Systemic renin-angiotensin system components and arteriovenous differences of angiotensin II (Ang II) and angiotensinogen (AGT) across abdominal subcutaneous adipose tissue and skeletal muscle were assessed in combination with measurements of tissue blood flow before and during systemic beta-adrenergic stimulation in 13 lean and 10 obese subjects. Basal plasma Ang II and AGT concentrations were not significantly different between lean and obese subjects. Ang II concentrations were increased in obese compared with lean subjects during beta-adrenergic stimulation (12.6+/-1.5 versus 8.1+/-1.0 pmol/L; P=0.04), whereas AGT concentrations remained unchanged. Plasma renin activity increased to a similar extent in lean and obese subjects during beta-adrenergic stimulation (both P<0.01). No net Ang II release across adipose tissue and skeletal muscle could be detected in both groups of subjects. However, AGT was released from adipose tissue and muscle during beta-adrenergic stimulation in obese subjects (both P<0.05). In conclusion, locally produced Ang II in adipose tissue and skeletal muscle exerts no endocrine role in lean and obese subjects. In contrast, AGT is released from adipose tissue and muscle in obese subjects during beta-adrenergic stimulation, which may contribute to the increased plasma Ang II concentrations during beta-adrenergic stimulation in obese subjects.

Bradykinin induced sustained anti–adrenergic actions in guinea pig heart muscle involves PKC

Objectives. Adenosine attenuates the effect of β-adrenergic stimulation upon contractile force, both when present during β-adrenergic stimulation and for a period after washout of adenosine. Protein kinase C (PKC) mediates the sustained effect. The present study investigated if bradykinin (500 nM) could induce anti-β-adrenergic actions. Design. Guinea pig papillary muscles (36.5°C, 1Hz) were subjected to 15 min exposure to and 20 min washout of bradykinin. Isoproterenol 100 nM was added for 3 min at the end of test exposure and at the end of washout. The PKC-inhibitor bisindolylmaleimide (20 nM) was given to investigate the importance of PKC. Results. Bradykinin significantly reduced the increase in contractile force in response to isoproterenol, both when present and after washout of test substance. Inhibition of PKC abolished the sustained effect, while inhibition of PI3-kinase with wortmannin did not seem to affect the results. Conclusions. Anti-β-adrenergic effects of bradykinin on contractile force and action potential duration were demonstrated. PKC was important for the sustained effect on contractile force, but not for the acute effect and the effect on action potential duration.

Exploring gonadal hormone involvement in male–female differences in the NK suppressive effects of β-adrenergic stimulation

Exploring gonadal hormone involvement in male–female differences in the NK suppressive effects of β-adrenergic stimulation