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Biomedical subjects

Kelly Stevens

Publications and source records attributed to Kelly Stevens.

6 recordsLinked to original sources
PubMed2006

Cannabinoid receptor-mediated inhibition of calcium signaling in rat retinal ganglion cells.

PURPOSE: The physiological actions of CB(1) cannabinoid receptors (CB(1)Rs) in mammalian retina have yet to be fully described in all cell types. Here we investigate the actions of CB(1)R activation on high-voltage-activated (HVA) Ca(2+) channel currents in purified cultures of rat retinal ganglion cells (RGCs). METHODS: Reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry were used to determine the presence of CB(1)R mRNA and protein in a purified RGC culture generated from neonatal rats using a two-step panning procedure. Ruptured-patch whole-cell voltage clamp was used to test the effect of CB(1)R agonists (WIN 55,212-2) and antagonists (SR141716A, AM281) on HVA Ca(2+) channel currents. RESULTS: RT-PCR analysis confirmed CB(1)R mRNA in cultured RGCs and immunocytochemistry for CB(1)R protein revealed labeling in both the cell body and neurites of isolated RGCs. Patch-clamp recording from cultured rat RGCs showed that the CB(1)R agonist WIN 55,212-2 inhibited HVA Ca(2+) channel currents up to 50% in a concentration-dependent manner (0.5, 1, and 5 muM). The Ca(2+) channel current inhibition by WIN 55,212-2 was blocked by CB(1)R antagonists AM281 and SR141716. CONCLUSIONS: Activation of CB(1)Rs in cultured RGCs inhibits HVA Ca(2+) channel currents. These data show that cannabinoids can modify the excitability of RGCs and could affect retinal output. This finding has implications for retinal signal processing as it suggests that endogenous cannabinoids have inhibitory effects on RGCs and that exogenous cannabinoids could modulate retinal function by this pathway as well.

Animals↗
PubMed2005

High-voltage-activated calcium channels in Muller cells acutely isolated from tiger salamander retina.

Muller cells mediate retinal function by stabilizing the ionic environment and signal glial network activity via calcium waves. Using whole-cell patch clamp recording, we describe a high-voltage-activated, slowly inactivating Ca channel current in isolated salamander Muller cells that has unusual pharmacological properties. The Ca channel current has an activation midpoint of approximately -8 mV and an inactivation midpoint of approximately -26 mV in 10 mM Ba2+. The time constant for inactivation is approximately 380 ms at potentials positive to zero. The current is blocked by Cd2+ with an EC50 of <100 nM. nisoldipine (10 microM) blocks approximately 50%, while nifedipine (1 microM), diltiazem (20 microM), and verapamil (50 microM) each block one-third of the current. In contrast to its typical actions, BayK 8644 blocks the current by approximately 25%. Blockers of other Ca channel subtypes were also tested: omega-agatoxin IVA (200 nM) blocked only 13% of the Ca channel current, while omega-conotoxin GVIA (1 microM) blocked 84% of the current. Immnohistochemistry supported the presence of alpha1A, alpha1B, alpha1C, and alpha1D Ca channel subunits. Mapping of dihydropyridine-binding sites with DM-BODIPY revealed a distribution of channels over the entire membrane of the Muller cell with a higher density at the apical region. Overall, these observations suggest either the presence of a mix of L- and N-type Ca channels or a single, unconventional HVA Ca channel subtype sharing L- and N-type Ca channel characteristics.

Ambystoma↗
PubMed2004

Factors influencing the publication of randomized controlled trials in child health research.

BACKGROUND: Publication bias threatens the validity of clinical decisions. The root causes are relatively unknown, and there is limited investigation in child research literature. OBJECTIVES: To identify factors associated with subsequent nonpublication of abstracts presented at the Society for Pediatric Research meetings, and to determine the relative importance of the reasons identified for nonpublication. DESIGN: A cross-sectional survey was used to ask researchers about their reasons for the selective publication of randomized controlled trials (RCTs). The authors of 393 RCTs presented at the Society for Pediatric Research meetings from 1992 to 1995 were surveyed. A modified Total Design Method for mail surveys was used, with a reminder sent to all potential respondents 1 week after the initial mailing and full mailings sent to nonrespondents at 3 and 10 weeks following the initial mailing. RESULTS: One hundred sixty-six (45%) completed surveys were returned, and 119 (72%) abstracts were published as full manuscripts. Factors significantly associated with nonpublication identified through multiple logistic regression were the respondent's report of scientific merit and significance of results. Of the 47 studies that were not published, only 8 (17%) had been submitted for publication. Authors of unpublished studies identified the following as important reasons for not publishing: not enough time (56.4 responded important or very important); trouble with coauthors (28.9); and journal unlikely to accept (26.3). CONCLUSIONS: Of the RCTs presented and not subsequently published, the majority (83%) were never submitted for publication. The most common reason cited by authors for nonpublication was lack of time.

Alberta↗
PubMed2002

Engineering endogenous inflammatory cells as delivery vehicles.

Leukocytes are central in directing host inflammatory and immune processes; therefore, leukocyte response to biomaterials is extremely important. Although several leukocyte-derived molecules are used clinically, the long-term efficacy of treatments involving the systemic administration of these bioactive agents has yet to be demonstrated. Hence, the localized delivery of selected cytokines and growth factors produced by endogenous leukocytes is desirable and may have potential therapeutic values in the fundamental processes of tissue healing, growth regulation, and biocompatibility. The specificity and diversity of ligand-receptor interactions offer an attractive method in manipulating cellular behavior. Therefore, a more detailed understanding of the interplay between ligands and cell membrane receptors must be obtained. We designed interleukin-1-derived biomimetic agonists and antagonists to study and modulate leukocyte function in vitro. Selected agonists increased GM-CSF release by adherent human blood-derived macrophages in the presence of the natural IL1beta antagonist, namely IL1ra. Furthermore, IL1-derived biomimetic antagonists neutralized the ability of IL1beta in increasing the release of GM-CSF by adherent macrophages. We employed similar methodologies to elucidate the molecular mechanisms of integrin and extracellular matrix interaction in regulating leukocyte function. Oligopeptides were designed based on the functional structure of fibronectin and grafted on to a polymer network containing polyethyleneglycols. Macrophage adhesion was independent of the peptide identity that contained sequence RGD, PHSRN, PRRARV, or combinations thereof in an integrin-dependent fashion in vitro. However, integrin-dependent FBGC formation in vitro was highly dependent on both RGD and PHSRN in a single peptide formulation and with a specific orientation. From our intracellular signaling studies in vitro, protein tyrosine and serine/threonine kinases were found important in integrin signaling leading to macrophage adhesion mediated by fibronectin-integrin association. Furthermore, RGD and PHSRN appear to be significant in mediating this receptor-ligand association resulting in the necessary signaling characteristic for macrophage adhesion and the subsequent development. Our in vivo results showed that peptide identity played a minimal role in modulating the host inflammatory response and adherent macrophage density. RGD-containing peptides mediated rapid FBGC formation by 4 days of implantation by significantly increasing both the number of macrophages that participate in the cell fusion process and the rate of cell fusion. Both RGD and PHSRN domains were important in mediating FBGC formation at later implantation periods. These findings represent a mechanistic correlation between the role of protein functional architectures in ligand-receptor recognition and the post-ligation signaling events that control cellular behavior in vitro and in vivo.

Amino Acid Sequence↗
PubMed2002

Abstracts of randomized controlled trials presented at the society for pediatric research meeting: an example of publication bias.

BACKGROUND: Publication bias toward studies that favor new therapies has been known to occur for the past 40 years, yet its implications are not well studied in child health. The increased interest in meta-analyses has highlighted the need to identify the totality of evidence when addressing treatment questions. OBJECTIVES: To measure the percentage of randomized controlled trials (RCTs) presented at a major pediatric scientific meeting that were subsequently published as full-length articles, to investigate factors associated with publication, and to describe the variables that change from abstract to manuscript form. DESIGN: The scientific proceedings from the Society for Pediatric Research were hand searched for RCTs (1992-1995). Subsequent publication was ascertained through a search of various electronic databases. Quality of abstracts and manuscripts was measured, and data were extracted using a structured form. RESULTS: A total of 264 (59.1%) of 447 abstracts were subsequently published. Almost 64% of RCTs that were subsequently published favored new therapy compared with 43.5% of studies that were never published (P<.001). Mean effect size for published vs unpublished RCTs was 0.74 vs 0.05 (P<.001). Median sample size was larger in published (n = 45) vs unpublished (n = 34) RCTs (P =.02). Quality was significantly lower for abstracts vs published RCTs (P<.001). For 5% of abstracts that were subsequently published, the conclusion regarding treatment efficacy changed. CONCLUSIONS: Publication bias is a serious threat to assessing the effectiveness of interventions in child health, as little more than half of RCTs presented at a major scientific meeting are subsequently published. There is a need to institute an international registry of RCTs in children so that the totality of evidence can be accessed when assessing treatment effectiveness.

Child↗