Search

Fenton RA, Shea LG, Doddi C, Dobson JG, Jr. Myocardial adenosine A1 -receptor-mediated adenoprotection involves phospholipase C, PKC-ϵ, and p38 MAPK, but not HSP27. Am J Physiol Heart Circ Physiol 298: H1671-H1678, 2010. First published April 2, 2010; doi: 10.11 52/ajpheart.0 1 028.2009.-Adenosine via an adenosine A1 receptor (A1R) is a negative feedback inhibitor of adrenergic stimulation in the heart, protecting it from toxic effects of overstimulation. Stimulation of the A1R results in the activation of Gi protein, release of free Gβ&#x03B3-subunits, and activation/translocation of PKC-ϵ to the receptor for activated C kinase 2 protein at the Z-line of the cardiomyocyte sarcomere. Using an anti-Gβ&#x03B3 peptide, we investigated the role of these subunits in the A1R stimulation of phospholipase C (PLC), with the premise that the resulting diacyiglycerol provides for the activation of PKC-ϵ. Inositol 1,4,5-triphosphate release was an index of PLC activity. Chlorocyclopentyl adenosine (CCPA), an R agonist, increased inositol I ,4,5-triphosphate production by 273% in mouse heart homogenates, an effect absent in A1R knockout hearts and inhibited by anti-Gi3-y peptide. In a second study, p38 MAPK and heat shock protein 27 (HSP27), found by others to be associated with the loss of myocardial contractile function, were postulated to play a role in the actions of A1R. Isoproterenol, a 3-adrenergic receptor agonist, increased the Ca2+ transient and sarcomere shortening magnitudes by 36 and 49%, respectively. In the rat cardiomyocyte, CCPA significantly reduced these increases, an action blocked by the p38 MAPK inhibitor SB-203580. While CCPA significantly increased the phosphorylation of HSP27, this action was inhibited by isoproterenol. These data indicate that the activation of PKC-ϵ by A1R results from the activation of PLC via free Gβ&#x03B3subunits released upon A1R-induced dissociation of Gay. Attenuation of β-adrenergic-induced contractile function by A1R may involve the activation of p38 MAPK, but not HSP27. [ABSTRACT FROM AUTHOR]

Adenosine protects the heart from adrenergic overstimulation. This adenoprotection includes the direct anti-adrenergic action via adenosine A receptors (A1R) on the adrenergic signaling pathway. An indirect A1R-induced attenuation of adrenergic responsiveness involves the translocation of PKC-ϵ to t-tubules and Z-line of cardiomyocytes. We investigated with sarcomere imaging, immunocytochemistry imaging, and coimmunoprecipitation (co-IP) whether R activation of PKC-ϵ induces the kinase translocation to receptor for activated C kinase 2 (RACK2) in isolated rat and mouse hearts and whether phospholipase C (PLC) is involved. Rat cardiomyocytes were treated with the A1R agonist chlorocyclopentyladenosine (CCPA) and exposed to primary PKC-ϵ and RACK2 antibodies with secondaries conjugated to Cy3 and Cy5 (indodicarbocyanine), respectively. Scanning confocal microscopy showed that CCPA caused PKC-ϵ to reversibly colocalize with RACK2 within 3 mm. Additionally, rat and mouse hearts were perfused and stimulated with CCPA or phenylisopropyladenosine to activate A1R, or with phorbol 12-myristate 13-acetate to activate PKC. RACK2 was immunoprecipitated from heart extracts and resolved with SDS-PAGE. Western blotting showed that CCPA, phenylisopropyladenosine, and phorbol 1, 2-myristate 13-acetate in the rat heart increased the PKC-ϵ co-IP with RACK2 by 186, 49, and >1,000%, respectively. The A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine prevented the CCPA-induced co-IP with RACK2. In mouse hearts, CCPA increased the co-IP of PKC-ϵ with RACK2 by 61%. With rat cardiomyocytes, the β-adrenergic agonist isoproterenol increased sarcomere shortening by 177%. CCPA reduced this response by 47%, an action inhibited by the PLC inhibitor U-73 122 and 8-cyclopentyl-1,3-dipropylxanthine. In conclusion, A1R stimulation of the heart is associated with PLC-initiated PKC-ϵ translocation and association with RACK2. [ABSTRACT FROM AUTHOR]

The adenosine A2A receptor (A2AR) enhances cardiac contractility, and the adeno- sine A1R receptor (A1R) is antiadrenergic by reducing the adrenergic ~ receptor (I3iR)-elicited increase in contractility. In this study we compared the A2AR-, A1R-, and 131R-elicited actions on isolated rat ventricular myocytes in terms of Ca transient and contractile re- sponses involving PKA and PKC. Stimulation of A2AR with 2 p~M (-.~EC50) CGS-21680 (CGS) produced a 17-28% increase in the Ca transient ratio (CTR) and maximum velocities (Vm~,,~) of transient ratio increase (+MVT) and recovery (-MVT) but no change in the time-to-50% recovery (TTR). CGS increased myocyte sarcomere shortening (MSS) and the maximum velocities of shortening (+MVS) and relaxation (-MVS) by 31-34% with no change in time-to-50% relengthening (TTL). ~1R stimulation using 2 nM (-~EC50) isopro- terenol (Iso) increased CTR, +MVT, and -MVT by 67-162% and decreased TTR by 43%. Iso increased MSS, +MVS, and -MVS by 153-174% and decreased TI'L by 31%. The A2AR and ~31R Ca transient and contractile responses were not additive. The PKA inhibitor Rp-adenosine 3' ,5 `-cyclic monophosphorothioate triethyla- monium salt prevented both the CGS- and Iso-elicited contractile responses. The PKC inhibitors chelerythrine and KJE1-l peptide (PKCe specific) prevented the antiadrenergic action of A1R but did not influence A2AR-mediated increases in contractile variables. The findings suggest that cardiac A2AR utilize cAMPIPKA like 31R, but the Ca transient and contractile responses are less in magnitude and not equally affected. Although PKC is important in the ~ R antiad- renergic action, it does not seem to play a role in A2AR-elicited Ca transient and contractile events. [ABSTRACT FROM AUTHOR]

Adenosine plays a role in regulating the contractile function of the heart. This includes a positive ionotropic action via the adenosine A2A receptor (A2AR) and an inhibition of β1-adrenergic receptor-induced ionotropy (antiadrenergic action) via the adenosine A1 receptor (A1R). Phosphatase activity has also been shown to influence contractile function by affecting the level of protein phosphorylation. Protein phosphatase 2A (PP2A) plays a significant role in mediating the A1R antiadrenergic effect. The purpose of this study was to investigate the effects of A2AR and A1R on the activities of PP2A in hearts obtained from wild-type (WT) and A2AR knockout (A2AR-KO) mice. PP2A activities were examined in myocardial particulate and cytoplasmic extract fractions. Treatment of wild-type hearts with the A1R agonist CCPA increased the total PP2A activity and increased the particulate:cytoplasmic PP2A activity ratio. Treatment with the A2AR agonist CGS-21680 (CGS) decreased the total PP2A activity and decreased the particulate:cytoplasmic PP2A activity ratio. This indicated a movement of PP2A activity between cell fractions. The effect of CCPA was inhibited by CGS. In A2AR-KO hearts the response to A1R activation was markedly enhanced whereas the response to A2AR activation was absent. These data show that A2AR and A1R regulate PP2A activity, thus suggesting an important mechanism for modulating myocardial contractility. J. Cell. Physiol. 216: 83–90, 2008. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The article focuses on the Community Care program in North Carolina. It describes the experience and the lessons learned from the program during the implementation of community health networks in the care of Medicaid recipients. It stresses that the program can be adapted as an effective system designed to achieve quality, utilization and cost objectives for the care of patients with chronic illness.

In the heart β1-adrenergic (β1R) and adenosine A1 (A1R) and A2A (A2AR) receptors modulate contractile and metabolic function. The interaction between these receptors was investigated at the level of G-protein cycling by determining the effect of receptor agonists on the binding of GTP to G-proteins and displacement of Gα-subunit-bound GDP by GTP. Crude membranes from rat heart or brain were stimulated by agonists for β1R (isoproterenol; ISO), A1R (chlorocyclopentyladenosine, CCPA) and A2AR (CGS-21680; CGS). GTP binding to membranes was increased by ISO (17%), CCPA (6%) and CGS (12%). Binding values observed with incubation using ISO and CCPA together were significantly less than values obtained by the incubation of individual agents alone. With ISO, GTP binding to Gαs subunits as determined by immunoprecipitation was increased 79% in heart and 87% in brain. These increases were attenuated by CCPA, an effect that was inhibited by CGS. GDP release by membranes was increased 6.9% and 4.6% by ISO and CCPA, respectively. After co-incubation of these agonists, release was increased less than determined by the addition of the individual agent responses. CGS inhibited the reduced release caused by of CCPA. Adenylyl cyclase activity stimulated by ISO was attenuated 33% by CCPA, an effect inhibited by CGS. Together, these results indicate that A1R exert an antiadrenergic action at the level of β1R stimulated Gs-protein cycling and that A2AR reduce this action. J. Cell. Physiol. 213:785–792. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Bursts of action potentials (APs) are crucial for the release of neurotransmitters from dense core granules. This has been most definitively shown for neuropeptide release in the hypothalamic neurohypophysial system (HNS). Why such bursts are necessary, however, is not well understood. Thus far, biophysical characterization of channels involved in depolarization-secretion coupling cannot completely explain this phenomenon at HNS terminals, so purinergic feedback mechanisms have been proposed. We have previously shown that ATP, acting via P2X receptors, potentiates release from HNS terminals, but that its metabolite adenosine, via A1 receptors acting on transient Ca2+ currents, inhibit neuropeptide secretion. We now show that endogenous adenosine levels are sufficient to cause tonic inhibition of transient Ca2+ currents and of stimulated exocytosis in HNS terminals. Initial non-detectable adenosine levels in the static bath increased to 2.9 µM after 40 min. These terminals exhibit an inhibition (39%) of their transient inward Ca2+ current in a static bath when compared to a constant perfusion stream. CPT, an A1 adenosine receptor antagonist, greatly reduced this tonic inhibition. An ecto-ATPase antagonist, ARL-67156, similarly reduced tonic inhibition, but CPT had no further effect, suggesting that endogenous adenosine is due to breakdown of released ATP. Finally, stimulated capacitance changes were greatly enhanced (600%) by adding CPT to the static bath. Thus, endogenous adenosine functions at terminals in a negative-feedback mechanism and, therefore, could help terminate peptide release by bursts of APs initiated in HNS cell bodies. This could be a general mechanism for controlling transmitter release in these and other CNS terminals. J. Cell. Physiol. 210: 309–314, 2007. © 2006 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The adenosine A1 receptor (A1R) inhibits β-adrenergic-induced contractile effects (antiadrenergic action), and the adenosine A2A receptor (A2AR) both opposes the A1R action and enhances contractility in the heart. This study investigated the A1R and A2AR function in p-adrenergic-stimulated, isolated wild-type and A2AR knockout murine hearts. Constant flow and pressure perfused preparations were employed, and the maximal rate of left ventricular pressure (LVP) development (+dp/dtmax) was used as an index of cardiac function. A1R activation with 2-chloro-N6-cyclopentyladenosine (CCPA) resulted in a 27% reduction in contractile response to the β-adrenergic agonist isoproterenol (ISO). Stimulation of A2AR with 2-P(2-carboxyethyl)phenethyl-amino-5' -N-ethylcarboxyamidoadenosine (CGS -21680) attenuated this antiadrenergic effect, resulting in a partial (constant flow preparation) or complete (constant pressure preparation) restoration of the ISO contractile response. These effects of A2AR were absent in knockout hearts. Up to 63% of the A2AR influence was estimated to be mediated through its inhibition of the A1R antiadrenergic effect, with the remainder being the direct contractile effect. Further experiments examined the effects of A2AR activation and associated vasodilation with low-flow ischemia in the absence of β-adrenergic stimulation. A2AR activation reduced by 5% the depression of contractile function caused by the flow reduction and also increased contractile performance over a wide range of perfusion flows. This effect was prevented by the A2AR antagonist 4-(2-[7- amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)-phenol (ZM-241 385). It is concluded that in the murine heart, A1R and A2AR modulate the response to β-adrenergic stimulation with A2AR, attenuating the effects of A1R and also increasing contractility directly. In addition, A2AR supports myocardial contractility in a setting of low-flow ischemia. [ABSTRACT FROM AUTHOR]

Adenosine-induced antiadrenergic effects in the heart are mediated by adenosine A1 receptors (A1R). The role of PKC∈ in the antiadrenergic action of adenosine was explored with adult rat ventricular myocytes in which PKC∈ was overexpressed. Myocytes were transfected with a pEGFP-N1 vector in the presence or absence of a PKC∈ construct and compared with normal myocytes. The extent of myocyte shortening elicited by electrical stimulation of quiescent normal and transfected myocytes was recorded with video imaging. PKC∈ was found localized primarily in transverse tubule's. The A1R agonist chlorocyclopentyladenosine (CCPA) at 1 µM rendered an enhanced localization of PKC∈ in the t-tubular system. The β-adrenergic agonist isoproterenol (Iso; 0.4 µM) elicited a 29-36% increase in myocyte shortening in all three groups. Although CCPA significantly reduced the Isoproduced increase in shortening in all three groups, the reduction caused by CCPA was greatest with PKC∈ overexpression. The CCPA reduction of the Iso-elicited shortening was eliminated in the presence of a PKC∈ inhibitory peptide. These results suggest that the translocation of PKC∈ to the t-tubular system plays an important role in A1R-mediated antiadrenergic actions in the heart. [ABSTRACT FROM AUTHOR]

Examines the properties of a biopolymer-free, brine-based low-solids, high-density reservoir drilling fluid during pretesting, mixing, drilling and completion. Rhelogical behavior; Viscosity; Gel strengths; Shale stability; Fluid reconditioning.

β-Adrenergic and antiadrenergic modulation of cardiac adenylyl cyclase is influenced by phosphorylation. Am J Physiol Heart Circ Physiol 285: H1471-H1478, 2003. First published June 12, 2003; 10.1152/ajpheart.00950. 2002.—Adenosine protects the myocardium of the heart by exerting an antiadrenergic action via the adenosine A[sub 1] receptor (A[sub 1]R). Because β[sub 1]-adrenergic receptor (B[sub 1]R) stimulation elicits myocardial protein phosphorylation, the present study investigated whether protein kinase A (PKA) catalyzed rat heart ventricular membrane phosphorylation affects the β[sub 1]R adrenergic and A[sub 1]R adenosinergic actions on adenylyl cyclase activity. Membranes were either phosphorylated with PKA in the absence/presence of a protein kinase inhibitor (PKI) or dephosphorylated with alkaline phosphatase (AP) and assayed for adenylyl cyclase activity (AC) in the presence of the β[sub 1]R agonist isoproterenol (ISO) and/or the A[sub 1]R agonist 2-chloro-N[sup 6]-cyclopentyladenosine (CCPA). [sup 32]P incorporation into the protein substrates of 140-120, 43, and 29 kDa with PKA increased both the ISO-elicited activation of AC by 51-54% and the A[sub 1]R-mediated reduction of the ISO-induced increase in AC by 29-50%, thereby yielding a total antiadrenergic effect of ∼78%. These effects of PICA were prevented by PKI. AP reduced the ISO-induced increase in AC and eliminated the antiadrenergic effect of CCPA. Immunoprecipitation of the solubilized membrane adenylyl cyclase with the use of a polyclonal adenylyl cyclase VI antibody indicated that the enzyme is phosphorylated by PKA. These results indicate that the cardioprotective effect of adenosine afforded by its antiadrenergic action is facilitated by cardiac membrane phosphorylation. [ABSTRACT FROM AUTHOR]

Inosine deriving from the metabolism of adenosine or inosine monophosphate (IMP) in the fibroblast provides the substrate for xanthine oxidase and is, therefore, an important source of toxic oxygen free radicals. With well-oxygenated medium, adenosine release appears to be greater for aged than young fibroblasts. In that the adenosine release by young cells is enhanced by reduced oxygenation, the effect anoxic stress on the release of the purine nucleosides adenosine and inosine by low-passage (PDL23-26; young) vs. high-passage (PDL 43–51; aged) human lung fibroblasts (IMR-90) was studied. Cultures of confluent fibroblasts were incubated for 16 hr under normoxic (NF) or anoxic (AF) atmospheres. The release of adenosine and inosine was determined by HPLC at 0, 3, 6 and 24 hr after termination of the 16-hr period. Immediately following anoxia (time 0), adenosine release by young AF was 29% greater than for young NF, whereas both the young AF and aged AF displayed a 34- and 21-fold greater inosine release, respectively, as compared to NF. With continued normoxic incubation for 3 hours inosine release by young and aged AF returned to levels observed with NF. However, with further normoxic incubation inosine release by aged AF again became elevated at 6 and 24 hr post-anoxia to values 3.0- to 5.3-fold those of NF. Deamination of the released adenosine was not the primary source of inosine. These data suggest that in the aged, but not young, fibroblast, anoxia initiates the induction of changes in purine metabolism which may potentially enhance the production of toxic peroxides and oxygen radicals upon return to normoxic conditions following an anoxic stress. [Copyright &y& Elsevier]

We present a class of exact solutions of the Einstein gravitational field equations describing spherically symmetric and static anisotropic stellar type configurations. The solution is represented in a closed integral form. The energy density and both radial and tangential pressure are finite and positive inside the anisotropic star. The energy density, radial pressure, pressure-density ratio and the adiabatic speed of sound are monotonically decreasing functions. Several stellar models with the anisotropy coefficient proportional to r² are discussed, the values of the basic physical parameters of the star (radius, mass and red shift) and bound on anisotropy parameter is obtained. [ABSTRACT FROM AUTHOR]

Short umbilical cord syndrome is an abnormality that consists of a short umbilical cord, an abdominal wall defect, and frequently severe scoliosis. Usually, the fetus has a normal karyotype. The authors report a case in which the fetus carried a maternally derived balanced translocation (Robertsonian, 13, 15 45XY, der 13;15) (q 10;q 10), a short umbilical cord (4 cm), and cystic hygromas. [ABSTRACT FROM AUTHOR]

Upper limits for the mass–radius ratio are derived for arbitrary general relativistic matter distributions in the presence of a cosmological constant. General restrictions for the redshift and total energy (including the gravitational contribution) for compact objects in the Schwarzschild–de Sitter geometry are also obtained in terms of the cosmological constant and of the mean density of the star. [ABSTRACT FROM AUTHOR]

In the article, the author discusses how to exploit the lessons learned from the COVID-19 pandemic to introduce change in health care for the better. Other topics include the issues in the U.S. health care system like the high medical costs and lack of preparedness in pandemic response, as well as how the reforms implemented by the Centers for Medicare & Medicaid Services resulted in the massive consolidation in the health care industry.

Investigates adenosine stimulation of DNA synthesis in human endothelial cells by measuring [3H]thymidine incorporation in cultures derived from human umbilical veins. Cell culture; CAMP and protein measurement; Stimulation of DNA synthesis by adenosine; Stimulation of DNA synthesis by adenine nucleotides.

Studies the role of interstitial adenosine in the reduced metabolic and mechanical responsiveness of the aged heart to beta-adrenergic stimulation. Comparison between young and aged rat hearts; Effect of isoproterenol; Effect of sulfophenyl-theophyline; Effect of exogenously administered adenosine deaminase.

Determines myocardial adenosine A1-receptor effectiveness during juvenile and adult stages of maturation. Augmentation of contractile and metabolic performance of the heart; Enhance expression of the antiadrenergic action of adenosine.