β2-Adrenergic receptor agonists stimulate L-type calcium current independent of PKA in newborn rabbit ventricular myocytes

Dopamine, Immunity, and Disease

The neurotransmitter dopamine is a key factor in central nervous system (CNS) function, regulating many processes including reward, movement, and cognition. Dopamine also regulates critical functions in peripheral organs, such as blood pressure, renal activity, and intestinal motility. Beyond these functions, a growing body of evidence indicates that dopamine is an important immunoregulatory factor. Most types of immune cells express dopamine receptors and other dopaminergic proteins, and many immune cells take up, produce, store, and/or release dopamine, suggesting that dopaminergic immunomodulation is important for immune function. Targeting these pathways could be a promising avenue for the treatment of inflammation and disease, but despite increasing research in this area, data on the specific effects of dopamine on many immune cells and disease processes remain inconsistent and poorly understood. Therefore, this review integrates the current knowledge of the role of dopamine in immune cell function and inflammatory signaling across systems. We also discuss the current understanding of dopaminergic regulation of immune signaling in the CNS and peripheral tissues, highlighting the role of dopaminergic immunomodulation in diseases such as Parkinson's disease, several neuropsychiatric conditions, neurologic human immunodeficiency virus, inflammatory bowel disease, rheumatoid arthritis, and others. Careful consideration is given to the influence of experimental design on results, and we note a number of areas in need of further research. Overall, this review integrates our knowledge of dopaminergic immunology at the cellular, tissue, and disease level and prompts the development of therapeutics and strategies targeted toward ameliorating disease through dopaminergic regulation of immunity. SIGNIFICANCE STATEMENT: Canonically, dopamine is recognized as a neurotransmitter involved in the regulation of movement, cognition, and reward. However, dopamine also acts as an immune modulator in the central nervous system and periphery. This review comprehensively assesses the current knowledge of dopaminergic immunomodulation and the role of dopamine in disease pathogenesis at the cellular and tissue level. This will provide broad access to this information across fields, identify areas in need of further investigation, and drive the development of dopaminergic therapeutic strategies.

Ventricular arrhythmias in acute myocardial ischaemia-Focus on the ageing and sex

Annually, approximately 17 million people die from cardiovascular diseases worldwide, half of them suddenly. The most common direct cause of sudden cardiac death is ventricular arrhythmia triggered by an acute coronary syndrome (ACS). The study summarizes the knowledge of the mechanisms of arrhythmia onset during ACS in humans and in animal models and factors that may influence the susceptibility to life-threatening arrhythmias during ACS with particular focus on the age and sex. The real impact of age and sex on the arrhythmic susceptibility within the setting of acute ischaemia is masked by the fact that ACSs result from coronary artery disease appearing with age much earlier among men than among women. However, results of researches show that in ageing process changes with potential pro-arrhythmic significance, such as increased fibrosis, cardiomyocyte hypertrophy, decrease number of gap junction channels, disturbances of the intracellular Ca²⁺ signalling or changes in electrophysiological parameters, occur independently of the development of cardiovascular diseases and are more severe in male individuals. A review of the literature also indicates a marked paucity of research in this area in female and elderly individuals. Greater awareness of sex differences in the aging process could help in the development of personalized prevention methods targeting potential pro-arrhythmic factors in patients of both sexes to reduce mortality during the acute phase of myocardial infarction. This is especially important in an era of aging populations in which women will predominate due to their longer lifespan.

Selective activation of adrenoceptors potentiates IKs current in pulmonary vein cardiomyocytes through the protein kinase A and C signaling pathways

Delayed rectifier K⁺ current (I_Ks) is a key contributor to repolarization of action potentials. This study investigated the mechanisms underlying the adrenoceptor-induced potentiation of I_Ks in pulmonary vein cardiomyocytes (PVC). PVC were isolated from guinea pig pulmonary vein. The action potentials and I_Ks current were recorded using perforated and conventional whole-cell patch-clamp techniques. The expression of I_Ks was examined using immunocytochemistry and Western blotting. KCNQ1, a I_Ks pore-forming protein was detected as a signal band approximately 100 kDa in size, and its immunofluorescence signal was found to be mainly localized on the cell membrane. The I_Ks current in PVC was markedly enhanced by both β₁- and β₂-adrenoceptor stimulation with a negative voltage shift in the current activation, although the potentiation was more effectively induced by β₂-adrenoceptor stimulation than β₁-adrenoceptor stimulation. Both β-adrenoceptor-mediated increases in I_Ks were attenuated by treatment with the adenylyl cyclase (AC) inhibitor or protein kinase A (PKA) inhibitor. Furthermore, the I_Ks current was increased by α₁-adrenoceptor agonist but attenuated by the protein kinase C (PKC) inhibitor. PVC exhibited action potentials in normal Tyrode solution which was slightly reduced by HMR-1556 a selective I_Ks blocker. However, HMR-1556 markedly reduced the β-adrenoceptor-potentiated firing rate. The stimulatory effects of β- and α₁-adrenoceptor on I_Ks in PVC are mediated via the PKA and PKC signal pathways. HMR-1556 effectively reduced the firing rate under β-adrenoceptor activation, suggesting that the functional role of I_Ks might increase during sympathetic excitation under in vivo conditions.

Modulation of cardiac stem cell characteristics by metoprolol in hypertensive heart disease

Cardiac stem cells (CSCs) play a vital role in cardiac remodeling. Uncontrolled hypertension leads to cardiac hypertrophy, followed by cardiac failure. Pathological remodeling is associated with enhanced oxidative stress. Decreased cardiac stem cell efficiency is speculated in heart diseases. Maintaining a healthy stem cell population is essential for preventing progressive cardiac remodeling. Some anti-hypertensive drugs are cardioprotective. However, the effect of these drugs on CSCs has not been investigated. Metoprolol is a cardioprotective anti-hypertensive agent. To examine whether metoprolol can prevent the deterioration of CSC efficiency, spontaneously hypertensive rats (SHRs) were treated with this drug, and the effects on stem cell function were evaluated. Six-month-old male SHRs were treated with metoprolol (50 mg × kg^-1per day) for 2 months. The effectiveness of the treatment at reducing blood pressure and reducing hypertrophy was ensured, and the animals were killed. Cardiac stem cells were isolated from the atrial tissue, and the effect of metoprolol on stem cell migration, proliferation, differentiation, and survival was evaluated by comparing the treated SHRs with untreated SHRs and normotensive Wistar rats. Compared to the Wistar rats, the SHR rats presented with a decrease in stem cell migration and proliferation and an increase in intracellular oxidative stress and senescence. Treating SHRs with metoprolol increased CSC migration and proliferation potential and stemness retention. Cellular senescence and oxidative stress were reduced. The attributes of stem cells from the metoprolol-treated SHRs were comparable to those of the Wistar rats. The restoration of stem cell efficiency is expected to prevent hypertension-induced progressive cardiac remodeling.

Cardiac voltage gated calcium channels and their regulation by β-adrenergic signaling

Voltage-gated calcium channels (VGCCs) are the predominant source of calcium influx in the heart leading to calcium-induced calcium release and ultimately excitation-contraction coupling. In the heart, VGCCs are modulated by the β-adrenergic signaling. Signaling through β-adrenergic receptors (βARs) and modulation of VGCCs by β-adrenergic signaling in the heart are critical signaling and changes to these have been significantly implicated in heart failure. However, data related to calcium channel dysfunction in heart failure is divergent and contradictory ranging from reduced function to no change in the calcium current. Many recent studies have highlighted the importance of functional and spatial microdomains in the heart and that may be the key to answer several puzzling questions. In this review, we have briefly discussed the types of VGCCs found in heart tissues, their structure, and significance in the normal and pathological condition of the heart. More importantly, we have reviewed the modulation of VGCCs by βARs in normal and pathological conditions incorporating functional and structural aspects. There are different types of βARs, each having their own significance in the functioning of the heart. Finally, we emphasize the importance of location of proteins as it relates to their function and modulation by co-signaling molecules. Its implication on the studies of heart failure is speculated.

The role of β-adrenergic receptors and p38MAPK signaling pathways in physiological processes of cardiosphere-derived cells

The effects of β adrenergic receptors (β-ARs) and p38 mitogen-activated protein kinases (MAPK) pathways on cardiosphere-derived cells (CDCs) are largely unknown. This study aimed to investigate the roles of β-ARs and p38MAPK pathways on the proliferation, apoptosis, and differentiation capacity of CDCs. The CDCs were treated with β1-AR blocker (Met group), β2-AR antagonist (ICI group), and p38MAPK inhibitor (SB group), non-selective β-AR blocker (PRO group), and β-AR agonist (ISO group). The viability, apoptotic rate and differentiation status of CDCs were determined by MST-1 assay, flow cytometery, and Western blot, respectively. The CDCs viability significantly reduced in ICI group (all P < 0.05), and SB group had a significant high viability after 48 h treatment (P < 0.05). Compared with control group, all treated groups had a low apoptotic rate. After treatment for 72 h, ISO treatment elevated the expression of Nkx2.5, and could partially or fully attenuate the inhibitory effects of β-AR antagonists and/or p38MAPK inhibitor. A similar overall trend of protein expression levels among all groups could be observed between protein pairs of cTnT and β1-AR as well as c-Kit and β2-AR, respectively. These results suggested that β-ARs and p38MAPK signaling pathways play crucial roles in the proliferation and differentiation of CDCs. Our findings should be helpful for better understanding the molecular mechanism underlying the physiological processes of CDCs.

Cardiac progenitor cells engineered with βARKct have enhanced β-adrenergic tolerance

Stem cell survival and retention in myocardium after injury following adoptive transfer is low. Elevated catecholamine levels coinciding with myocardial injury adversely affect cardiac progenitor cell (CPC) survival. The G protein-coupled receptor kinase 2 (GRK2)-derived inhibitory peptide, βARKct, enhance myocyte contractility, survival, and normalize the neurohormonal axis in failing heart, however salutary effects of βARKct on CPC survival and proliferation are unknown. Herein, we investigated whether the protective effects of βARKct expression seen in the failing heart relate to CPCs. Modified CPCs expressing βARKct enhanced AKT/eNOS signaling through protective β2-adrenergic receptors (β2-ARs). In addition, to the actions of βARKct expression on β2- AR signaling, pharmacologic inhibition of GRK2 also increased β2-AR signaling in nonengineered CPCs (lacking βARKct) but had limited effects in βARKct engineered CPCs providing evidence for the strength of the βARKct in inhibiting GRK2 in these cells. Increased proliferation and metabolic activity were observed in βARKct-engineered CPCs following catecholamine stimulation indicating improved adrenergic tolerance. βARKct modification of CPCs increased survival and proliferation following adoptive transfer in an acute myocardial infarction model concomitant with increased expression of β-AR. Thus, βARKct engineering of CPCs promotes survival and proliferation of injected cells following myocardial infarction, which includes improved β-adrenergic tolerance essential for stem cell survival.

β-Adrenergic regulation of cardiac progenitor cell death versus survival and proliferation

RATIONALE

Short-term β-adrenergic stimulation promotes contractility in response to stress but is ultimately detrimental in the failing heart because of accrual of cardiomyocyte death. Endogenous cardiac progenitor cell (CPC) activation may partially offset cardiomyocyte losses, but consequences of long-term β-adrenergic drive on CPC survival and proliferation are unknown.

OBJECTIVE

We sought to determine the relationship between β-adrenergic activity and regulation of CPC function.

METHODS AND RESULTS

Mouse and human CPCs express only β2 adrenergic receptor (β2-AR) in conjunction with stem cell marker c-kit. Activation of β2-AR signaling promotes proliferation associated with increased AKT, extracellular signal-regulated kinase 1/2, and endothelial NO synthase phosphorylation, upregulation of cyclin D1, and decreased levels of G protein-coupled receptor kinase 2. Conversely, silencing of β2-AR expression or treatment with β2-antagonist ICI 118, 551 impairs CPC proliferation and survival. β1-AR expression in CPC is induced by differentiation stimuli, sensitizing CPC to isoproterenol-induced cell death that is abrogated by metoprolol. Efficacy of β1-AR blockade by metoprolol to increase CPC survival and proliferation was confirmed in vivo by adoptive transfer of CPC into failing mouse myocardium.

CONCLUSIONS

β-adrenergic stimulation promotes expansion and survival of CPCs through β2-AR, but acquisition of β1-AR on commitment to the myocyte lineage results in loss of CPCs and early myocyte precursors.

Pathophysiological relevance of the cardiac β2-adrenergic receptor and its potential as a therapeutic target to improve cardiac function

β-adrenoceptors are members of the G protein-coupled receptor superfamily which play a key role in the regulation of myocardial function. Their activation increases cardiac performance but can also induce deleterious effects such as cardiac arrhythmias or myocardial apoptosis. In fact, inhibition of β-adrenoceptors exerts a protective effect in patients with sympathetic over-stimulation during heart failure. Although β(2)-adrenoceptor is not the predominant subtype in the heart, it seems to importantly contribute to the cardiac effects of adrenergic stimulation; however, the mechanism by which this occurs is not fully understood. This review summarizes the current knowledge on the role of β(2)-adrenoceptors in the regulation of cardiac contractility, metabolism, cardiomyocyte survival and cardiac arrhythmias. In addition, therapeutic considerations relating to stimulation of the β(2)-adrenoceptor such as an increase in cardiac contractility with low arrythmogenic effect, protection of the myocardium again apoptosis or positive regulation of heart metabolism are discussed.

Phosphodiesterases inhibition unmask a positive inotropic effect mediated by beta2-adrenoceptors in rat ventricular myocardium

The effects of salbutamol on contractility and cAMP levels were investigated in rat right ventricular myocardium. Salbutamol (1-300 microM), produced a concentration-dependent positive inotropic effect which was not affected by ICI 118551 (50 nM), a beta2-adrenoceptor antagonist but was abolished by CGP 20712A (1 microM) a beta1-adrenoceptor antagonist. However, in rats pretreated with pertussis toxin (30 microg/kg intraperitoneal injection) salbutamol increases contractility (Emax = 9.8 +/- 1.8%, - log EC50 = 6.25 +/- 0.07, n = 5). The combination of salbutamol + CGP 20712A, also produces a concentration-dependent enhancement of contractility (Emax = 43.0 +/- 7.5%, - log EC50 = 6.3 +/- 0.04, n = 6), in the presence of 30 microM of the non selective phosphodiesterase (PDE) inhibitor 3-isobutylmethylxantine (IBMX) which was prevented by ICI 118551 (50 nM). Also, salbutamol + CGP 20712A fail to increase cAMP tissue levels but enhance them in the presence of IBMX. This effect was also prevented by ICI 118551. These results indicate that PDEs blunt contractility and cAMP production mediated by beta2-adrenoceptors in rat ventricular myocardium. Gi protein, although less efficiently than PDEs, also limits inotropic effects of salbutamol mediated by beta2-adrenoceptors in this tissue.

Regulation of cardiac excitation and contraction by p21 activated kinase-1

Cardiac excitation and contraction are regulated by a variety of signaling molecules. Central to the regulatory scheme are protein kinases and phosphatases that carry out reversible phosphorylation of different effectors. The process of beta-adrenergic stimulation mediated by cAMP dependent protein kinase (PKA) forms a well-known pathway considered as the most significant control mechanism in excitation and contraction as well as many other regulatory mechanisms in cardiac function. However, although dephosphorylation pathways are critical to these regulatory processes, signaling to phosphatases is relatively poorly understood. Emerging evidence indicates that regulation of phosphatases, which dampen the effect of beta-adrenergic stimulation, is also important. We review here functional studies of p21 activated kinase-1 (Pak1) and its potential role as an upstream signal for protein phosphatase PP2A in the heart. Pak1 is a serine/threonine protein kinase directly activated by the small GTPases Cdc42 and Rac1. Pak1 is highly expressed in different regions of the heart and modulates the activities of ion channels, sarcomeric proteins, and other phosphoproteins through up-regulation of PP2A activity. Coordination of Pak1 and PP2A activities is not only potentially involved in regulation of normal cardiac function, but is likely to be important in patho-physiological conditions.

Prostaglandin receptors mediate effects of substances released from ischaemic rat hearts on non-ischaemic cardiomyocytes

BACKGROUND

After ischaemia and during reperfusion, rat hearts release cardiodepressive substances that are putatively cyclooxygenase-2-dependent. The present study analyses the mechanisms by which these substances mediate their effect downstream of cyclooxygenase-2.

MATERIALS AND METHODS

After 10 min of global stop-flow ischaemia, isolated rat hearts were reperfused and post-ischaemic coronary effluent was collected over a period of 30 s. Non-ischaemic effluent collected before ischaemia was used as a control. We investigated the effect of the effluents on cell shortening and Ca(++)-metabolism, by application of fluorescence microscopy of field-stimulated adult rat cardiomyocytes incubated with fura-2. Cells were pre-incubated with inhibitors of protein kinase A and C and with antagonists of protein kinase A-dependent prostaglandin receptors. We examined the expression of prostaglandin receptors in cardiomyocytes by Western blotting.

RESULTS

In contrast to non-ischaemic effluent, post-ischaemic effluent induced reduction of Ca(++) transient and cell shortening in the cardiomyocytes. In contrast to protein kinase C inhibitor Myr-PKC [19-27], the protein kinase A inhibitor Rp-cAMPS completely blocked the effect of post-ischaemic effluent. Furthermore, we determined a cyclic adenosine monophosphate increase in cardiomyocytes that were pre-incubated with post-ischaemic effluent. The antagonist of prostaglandin E-receptor EP2 AH6809 and the antagonist of receptor subtype EP4 AH23848 attenuated the effect of post-ischaemic effluent in contrast to other antagonists of prostaglandin D and I receptors, which did not influence the effect. In lysates of adherend cardiomyocytes, expression of prostaglandin D, E and I receptors was detected by Western blotting.

CONCLUSIONS

The effect of post-ischaemic effluent is mediated by the protein kinase A-dependent prostaglandin-receptor subtypes EP2 and EP4 downstream of cyclooxygenase-2.

Dopamine increases L-type calcium current more in newborn than adult rabbit cardiomyocytes via D1 and β2 receptors

Dopamine is used to treat heart failure, particularly after cardiac surgery in infants, but the mechanisms of action are unclear. We investigated differences in the effect of dopamine on L-type calcium current ( ICa) between newborn (NB, 1–4 days) and adult (AD, 3–4 mo) rabbit ventricular myocytes. Myocytes were enzymatically dissociated from NB and AD rabbit hearts. ICa was recorded by using the whole cell patch-clamp technique. mRNA levels of cardiac dopamine receptor type 1 (D1), type 2 (D2), and β-adrenergic receptors (β-ARs) were measured by real-time RT-PCR. Dopamine (100 μM) increased ICa more in NB (Emax 87 ± 10%) than in AD ventricular cells (Emax 21 ± 3%). Further investigation of this difference showed that mRNA levels of the D1 receptor were significantly higher in NB, and, with β-AR blockade, dopamine increased ICa more in NB than AD cells. Additionally, SKF-38393 (selective D1 receptor agonist) significantly increased ICa by 55 ± 4% in NB ( P < 0.05, n = 4) and by 11 ± 1% in AD ( P < 0.05, n = 6). Dopamine in the presence of SCH-23390 (D1 receptor antagonist) increased ICa in NB cells by 67 ± 5% and by 22 ± 2% in AD cells, suggesting a role for β-AR stimulation. Selective blockade of β1- or β2-receptors (with block of D1 receptors) showed that the β-AR action of dopamine in the NB was largely mediated via β2-AR activation. Dopamine produces a larger increase in ICa in NB cardiomyocytes compared with ADs. The mechanism of action is not only through β2-ARs but also due to higher expression of cardiac D1 receptor in NB.