Localization of calcitonin gene-related peptide in cardiomyocytes: comparison of neonatal and dedifferentiating cells to adult myocytes

Inotropic and lusitropic effects of calcitonin gene-related peptide in the heart

Previous studies have demonstrated positive-inotropic effects of calcitonin gene-related peptide (CGRP), but the mechanisms remain unclear. Therefore, two experiments were performed to determine the physiological correlates of the positive-inotropic effects of CGRP. Treatments designed to antagonize the effects of physiologically active CGRP₁₋₃₇ included posttreatment with CGRP₈₋₃₇ and pretreatment with LY-294002 (LY, an inhibitor of phosphatidylinositol 3-kinase), 17β-estradiol (E), and progesterone (P) were also used to modulate the effects of CGRP₁₋₃₇. Experiment 1 was in vitro studies on sarcomeres and cells of isolated adult rat cardiac myocytes. CGRP₁₋₃₇, alone and in combination with E and P, decreased sarcomere shortening velocities and increased shortening percentages, effects that were antagonized by CGRP₈₋₃₇, but not by LY. CGRP₁₋₃₇ increased resting intracellular calcium ion concentrations and Ca(2+) influxes, effects that were also antagonized by both CGRP₈₋₃₇ and LY. Experiment 2 was in vivo studies on left ventricular pressure-volume (PV) loops. CGRP₁₋₃₇ increased end-systolic pressure, ejection fraction, and velocities of contraction and relaxation while decreasing stroke volume, cardiac output, stroke work, PV area, and compliance. After partial occlusion of the vena cava, CGRP₁₋₃₇ increased the slope of the end-systolic PV relationship. CGRP₈₋₃₇ and LY attenuated most of the CGRP-induced changes. These findings suggest that CGRP-induced positive-inotropic effects may be increased by treatments with estradiol and progesterone and inhibited by LY. The physiological correlates of CGRP-induced positive inotropy observed in rat sarcomeres, cells, and intact hearts are likely to reveal novel mechanisms of heart failure in humans.

Liposomal modular complexes for simultaneous targeted delivery of bioactive gases and therapeutics

Intrinsically echogenic liposomes (ELIP) can be adapted to encapsulate nitric oxide to facilitate ultrasound-enhanced delivery of therapeutic agents to atherosclerotic plaques. However, the NO loading of targeted ELIP caused a 93% decrease of antibody (Ab) immunoreactivity. The following hypothesis was tested: biotin/avidin-mediated coupling of NO-ELIP and Ab-conjugated ELIP will enable co-delivery of bioactive gases and ELIP that can encapsulate other agents without loss of targeting efficiency. Complex formation was initiated by addition of excess streptavidin to equal proportions of biotinylated Ab-ELIP and NO-ELIP. Fluorescence deconvolution microscopy, Coulter Multisizer 3 analysis and flow cytometry demonstrated that the ELIP coupling procedure formed mixed aggregates of >or=10 liposomes within 1 min. Intravascular ultrasound imaging and ELISA showed that echogenicity and targeting efficiency were completely and 69-99% retained, respectively. When complexed to NO-ELIP, ELIP bifunctionally targeted to both CD34 and ICAM-1 (BF-ELIP) increased human mononuclear cell migration through human coronary artery endothelial cell monolayers in transwell plates 4-fold relative to a nonspecific IgG-ELIP control and 2-fold relative to BF-ELIP alone. It was concluded that this novel multi-functional conjugation methodology provides a platform technology for site-specific co-delivery of bioactive gases and other agents.

Fluorescence microscopy and 3D image reconstruction of cytokine initiated disruption of the Parkinson disease associated proteins alpha-synuclein, tau and ubiquitin in cultured glial cells

Human derived glioblastoma cells were cultured and treated with cytokines interleukin-6 (IL6), tumor necrosis factor alpha (TNF) and interferon-gamma (IFN) and imaged by fluorescence deconvolution microscopy to localize alpha-synuclein, tau and ubiquitin. Exposures were for short (2 h) and prolonged times (up to 96 h), with doses at both low (10 ng/ml), and high (100 ng/ml) concentrations. Further experiments used additive doses up to 200 ng/ml (2 x 100 ng), mimicking a super-infection state. Single, low doses of the cytokines initiated changes in levels of intracellular proteins, but these changes, be they increases or decreases, were not sustained, so we added higher doses of cytokine to the culture medium or fresh aliquots of cytokines over time. Finally, we treated cells with high, single doses of cytokine (200 ng/ml), to try to sustain perturbations of the proteins with cytokines. IFN caused a disruption and reduction of peripheral synuclein, TNF treatment resulted in increased levels of ubiquitin and IL6 disrupted and appeared to fragment tau. Of note, each of the proteins was found in a specific locale, tau being perinuclear, ubiquitin residing in the cytoplasm, and alpha-synuclein occupying the tips of cellular processes, exhibiting the characteristics of an adhesion protein/molecule [Word count=198].

CGRP-alpha responsiveness of adult rat ventricular cardiomyocytes from normotensive and spontaneously hypertensive rats

Calcitonin gene-related peptide (CGRP)-alpha is expressed in heart ventricles in sensory nerves and cardiomyocytes. It modifies inotropism and induces ischaemic preconditioning. This study investigates the effect of CGRP-alpha on the contractile responsiveness of isolated adult ventricular rat cardiomyocytes and the effect of chronic hypertension on this interaction. Cardiomyocytes were isolated and paced at 0.5-2.0 Hz. Cell shortening was recorded via a line camera with a reading frame of 500 Hz. CGRP-alpha exerted a dual effect on cardiomyocytes with a positive contractile effect at 10nM and a negative contractile effect at 10 pM. CGRP-alpha(8-37), a calcitonin receptor-like receptor (CRLR) antagonist, attenuated the positive contractile effect. H89, a protein kinase A antagonist, converted the positive contractile effect into a negative contractile effect. The negative contractile effect was converted again back to a positive contractile effect in the presence of l-nitro arginine. In cardiomyocytes isolated from spontaneously hypertensive rats (SHR) the mRNA expression of CRLR and the receptor-associated modifier protein (RAMP)-2 were lower. However, on the protein level CLRL was up-regulated, RAMP2 expression remained unchanged, and eNOS expression was down-regulated in these cells. These cells responded with a pure positive contractile response. In Langendorff preparations, CGRP-alpha slightly reduced the rate pressure product in hearts from normotensive rats but it caused an increase in hearts from SHR. In conclusion, it is shown that CGRP-alpha exerts dual effects on cardiomyocytes favouring the negative contractile effect at very low concentrations. This effect is compensated in chronic pressure-overloaded hearts and converted into a positive inotropism.

Oleandrin produces changes in intracellular calcium levels in isolated cardiomyocytes: a real-time fluorescence imaging study comparing adult to neonatal cardiomyocytes

Oleanders are common, hardy shrubs that grow throughout the southern United States. They contain cardiotonic steroids formed from cardenolides and bufadienolides, making the plant poisonous to both animals and humans. Aliquots of both commercially available oleander and fresh oleander extracts were prepared. Fresh, rod-like, calcium-tolerant adult rat cardiomyocytes and cultured neonatal cardiomyocytes were isolated and treated with 0-4 ng/ml of both preparations, challenged with verapamil and ouabain, and real-time spectrophotometric calcium transients and images were acquired. A number of effects were observed with the adult cells: (1) intracellular calcium levels were increased in a concentration-dependent manner: (2) reduced calcium transient heights and eventual cessation of beating resulted; and (3) increased sparking intensity led to subsequent beating and eventual calcium overload. In the spontaneously beating cultured neonatal myocytes increased intramyocytic calcium levels were also seen, with retention of this calcium rise leading to overload and, as in the adult myocytes, cessation of beating. These observations demonstrate that oleander extract is markedly potent with respect to the elevation of calcium concentrations in cardiomyocytes, and that the inability of the cardiomyocytes to release the accumulated calcium possibly indicates a role for oleandrin in inhibition of ryanodine receptor calcium release channels, calcium uptake via Na+,K+-ATPase inhibition [EC 3.6.1.3], and/or dysfunction of sarcolemmal calcium release channels.

Unique matrix structure in the rough endoplasmic reticulum cisternae of pseudoachondroplasia chondrocytes

Mutations in cartilage oligomeric matrix protein (COMP) cause two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED/EDM1). Because COMP exists as a homopentamer, only one mutant COMP subunit may result in an abnormal complex that is accumulated in expanded rough endoplasmic reticulum (rER) cisternae, a hallmark of PSACH. Type IX collagen and matrilin-3 (MATN3), also accumulate in the rER cisternae of PSACH chondrocytes, but it is unknown how mutant COMP interacts with these proteins. The studies herein focus on defining the organization of these intracellularly retained proteins using fluorescence deconvolution microscopy. A unique matrix organization was identified in which type II procollagen formed a central core surrounded by a protein network of mutant COMP, type IX collagen, and MATN3. This pattern of matrix organization was found in multiple cisternae from single chondrocytes and in chondrocytes with different COMP mutations, indicating a common pattern of interaction. This suggests that stalling of mutant COMP and an interaction between mutant COMP and type II procollagen are initiating events in the assembly of matrix in the rER, possibly explaining why the material is not readily cleared from the rER. Altogether, these data suggest that mutant COMP initiates and perhaps catalyzes premature intracellular matrix assembly.

Determination of the site of action of calcitonin gene-related peptide in the alteration of intracellular calcium levels in adult and neonatal rodent myocytes

The purpose of this study is to elucidate the mechanism of action and site of action of calcitonin gene-related peptide (CGRP) and its effects on calcium concentrations in two types of cardiomyocytes, neonatal and adult, by employing real-time fluorescence imaging. CGRP caused an increase in intramyocytic calcium with adult cells, but a decrease with neonates. Treatment of adult myocytes with ouabain and ryanodine yielded results suggesting that CGRP action is not at the ryanodine receptor (RyR) and does not involve Na+ +K+ ATPase. Furthermore, in neonatal cardiomyocytes CGRP caused a reduction in intramyocytic calcium levels, and challenges with ryanodine and ouabain gave results supporting the hypothesis that CGRP acts at the sarcolemmal L-type calcium channel. Employing real-time fluorescence measurements in cultured, dedifferentiated adult cardiomyocytes, which are known to express a fetal phenotype and exhibit neonatal-like calcium transients, our acquisitions demonstrated a major reduction in intracellular calcium levels. Finally, our collaborative studies in human myocardium using fluorescence deconvolution microscopy revealed that CGRP localization was found in a pattern similar to that of the sarcolemmal L-type calcium channel.