Dr. Steven  Parker  Dds image

Dr. Steven Parker Dds

2415 Musgrove Rd #309
Silver Spring MD 20904
301 847-7800
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #: 04922
NPI: 1609990787
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Homoiterons and expansion in ribosomal RNAs. - FEBS open bio
Ribosomal RNAs in both prokaryotes and eukaryotes feature numerous repeats of three or more nucleotides with the same nucleobase (homoiterons). In prokaryotes these repeats are much more frequent in thermophile compared to mesophile or psychrophile species, and have similar frequency in both large RNAs. These features point to use of prokaryotic homoiterons in stabilization of both ribosomal subunits. The two large RNAs of eukaryotic cytoplasmic ribosomes have expanded to a different degree across the evolutionary ladder. The big RNA of the larger subunit (60S LSU) evolved expansion segments of up to 2400 nucleotides, and the smaller subunit (40S SSU) RNA acquired expansion segments of not more than 700 nucleotides. In the examined eukaryotes abundance of rRNA homoiterons generally follows size and nucleotide bias of the expansion segments, and increases with GC content and especially with phylogenetic rank. Both the nucleotide bias and frequency of homoiterons are much larger in metazoan and angiosperm LSU compared to the respective SSU RNAs. This is especially pronounced in the tetrapod vertebrates and seems to culminate in the hominid mammals. The stability of secondary structure in polyribonucleotides would significantly connect to GC content, and should also relate to G and C homoiteron content. RNA modeling points to considerable presence of homoiteron-rich double-stranded segments especially in vertebrate LSU RNAs, and homoiterons with four or more nucleotides in the vertebrate and angiosperm LSU RNAs are largely confined to the expansion segments. These features could mainly relate to protein export function and attachment of LSU to endoplasmic reticulum and other subcellular networks.
G and C Iterons and Strings in MicroRNAs Should be Important in Regulation of mRNAs(†). - MicroRNA (Shāriqah, United Arab Emirates)
Same-nucleotide repeats (iterons) are strongly expressed in many DNA regions and RNA classes. These repeats serve importantly in association of polynucleotides and proteins, but have not been characterized in miRNAs.Iterons and nucleotide strings were quantified in currently known human miRNAs, including some comparisons with miRNAs of other species.Human 5p miRNAs have significantly more G iterons than other miRNA groups. The 3p miRNAs have an inverse excess of C iterons. The miRNAs lacking functional counter-stems (which we differentiate as 5n or 3n by position in pre-miRNAs) also have a large excess of G iterons. In 5p miRNAs G and C iterons have much higher density in the seed compared to the post-seed region. This difference is lower in 5n and 3n sequences, and much lower in 3p sequences. In all groups the contiguous GC strings constitute a larger part of sequences than the AU strings. A surplus of G or C iterons and of GC strings should enable a more stable association with the target mRNAs.From the available evidence, the G iteron- and GC-rich miRNAs should also interact more readily with miRNA-processing and similar proteins.
The protozoan, Paramecium primaurelia, as a non-sentient model to test laser light irradiation: The effects of an 808nm infrared laser diode on cellular respiration. - Alternatives to laboratory animals : ATLA
Photobiomodulation (PBM) has been used in clinical practice for more than 40 years. Unfortunately, conflicting literature has led to the labelling of PBM as a complementary or alternative medicine approach. However, past and ongoing clinical and research studies by reputable investigators have re-established the merits of PBM as a genuine medical therapy, and the technique has, in the last decade, seen an exponential increase in the numbers of clinical instruments available, and their applications. This resurgence has led to a clear need for appropriate experimental models to test the burgeoning laser technology being developed for medical applications. In this context, an ethical model that employs the protozoan, Paramecium primaurelia, is proposed. We studied the possibility of using the measure of oxygen consumption to test PBM by irradiation with an infrared or near-infrared laser. The results show that an 808nm infrared laser diode (1W; 64J/cm²) affects cellular respiration in P. primaurelia, inducing, in the irradiated cells, a significantly (p < 0.05) increased oxygen consumption of about 40%. Our findings indicate that Paramecium can be an excellent tool in biological assays involving infrared and near-infrared PBM, as it combines the advantages of in vivo results with the practicality of in vitro testing. This test represents a fast, inexpensive and straightforward assay, which offers an alternative to both traditional in vivo testing and more expensive mammalian cellular cultures.2015 FRAME.
Achieving Dental Analgesia with the Erbium Chromium Yttrium Scandium Gallium Garnet Laser (2780 nm): A Protocol for Painless Conservative Treatment. - Photomedicine and laser surgery
The aim of this research is to evaluate those techniques and optimal parameters of Erbium Chromium Yttrium Scandium Gallium Garnet (Er,Cr:YSGG) laser use in delivering predictable painless (or with very limited discomfort) restorative cavity preparation without the aid of injected local anesthesia.This study was conducted on 30 patients (26 adults and 4 youth 9-16 years old; average age, 37) treated in a private practice. For each patient, a single cavity was prepared using the Er,Cr:YSGG laser (2780 nm). An Electric Pulp Tester (EPT) was used to monitor the changes in pulp sensibility threshold. The patient experience was tested before and after the treatment using a modified Visual Analogue Scale (VAS) and Children's Fear Survey Schedule-Dental Subscale (CFSS-DS) to evaluate pain and anxiety.Pain analysis indicated that 80% of patients (24 out of 30) felt no pain and no discomfort, or only a very slight sensation. None of the 30 patients requested anesthesia. EPT was found to be unreliable in evaluating pulpal pain threshold levels. A tendency was noted wherein greater discomfort was felt by anxious patients. On average, the older the patient, the less discomfort was felt. The factors that have a greater tendency to promote discomfort were: posterior teeth, greater caries depth, greater use of higher power levels and ablation time.Using the Er,Cr:YSGG laser, it was possible to avoid local anesthesia during cavity preparation with a bur. The treatment was effective in a high number of cases (80%), leading to reduction in the anxiety frequently associated with dental care.
Effect of 808 nm Diode Laser on Swimming Behavior, Food Vacuole Formation and Endogenous ATP Production of Paramecium primaurelia (Protozoa). - Photochemistry and photobiology
Photobiomodulation (PBM) has been used in clinical practice for more than 40 years. To clarify the mechanisms of action of PBM at cellular and organism levels, we investigated its effect on Paramecium primaurelia (Protozoa) irradiated by an 808 nm infrared diode laser with a flat-top handpiece (1 W in CW). Our results led to the conclusion that: (1) the 808 nm laser stimulates the P. primaurelia without a thermal effect, (2) the laser effect is demonstrated by an increase in swimming speed and in food vacuole formation, (3) the laser treatment affects endogenous adenosine triphosphate (ATP) production in a positive way, (4) the effects of irradiation dose suggest an optimum exposure time of 50 s (64 J cm(-2) of fluence) to stimulate the Paramecium cells; irradiation of 25 s shows no effect or only mild effects and irradiation up to 100 s does not increase the effect observed with 50 s of treatment, (5) the increment of endogenous ATP concentration highlights the positive photobiomodulating effect of the 808 nm laser and the optimal irradiation conditions by the flat-top handpiece.© 2015 The American Society of Photobiology.
Paramecium: a promising non-animal bioassay to study the effect of 808 nm infrared diode laser photobiomodulation. - Photomedicine and laser surgery
Photobiostimulation and photobiomodulation (PBM) are terms applied to the manipulation of cellular behavior using low intensity light sources, which works on the principle of inducing a biological response through energy transfer. The aim of this investigation was to identify a laboratory assay to test the effect of an infrared diode laser light (808 nm) on cell fission rate.Sixty cells of Paramecium primaurelia were divided in two groups of 30. The first group (test group) was irradiated, at a temperature of 24°C, for 50 sec by a 808 nm diode laser with a flat top handpiece [1 cm of spot diameter, 1 W in continuous wave (CW), 50 sec irradiation time, 64 J/cm(2) of fluence]. The second group (control group) received no laser irradiation. All cells were transferred onto a depression slide, fed, and incubated in a moist chamber at a temperature of 24°C. The cells were exposed and monitored for 10 consecutive fission rates. Changes in temperature and pH were also evaluated.The exposed cells had a fission rate rhythm faster than the control cells, showing a binary fission significantly (p<0.05) shorter than unexposed cells. No significant effects of laser irradiation on pH and temperature of Paramecium's lettuce infusion medium were observed.The 808 nm infrared diode laser light, at the irradiation parameters used in our work, results in a precocious fission rate in P. primaurelia cells, probably through an increase in metabolic activity, secondary to an energy transfer.
Dimers of G-protein coupled receptors as versatile storage and response units. - International journal of molecular sciences
The status and use of transmembrane, extracellular and intracellular domains in oligomerization of heptahelical G-protein coupled receptors (GPCRs) are reviewed and for transmembrane assemblies also supplemented by new experimental evidence. The transmembrane-linked GPCR oligomers typically have as the minimal unit an asymmetric ~180 kDa pentamer consisting of receptor homodimer or heterodimer and a G-protein αβγ subunit heterotrimer. With neuropeptide Y (NPY) receptors, this assembly is converted to ~90 kDa receptor monomer-Gα complex by receptor and Gα agonists, and dimers/heteropentamers are depleted by neutralization of Gαi subunits by pertussis toxin. Employing gradient centrifugation, quantification and other characterization of GPCR dimers at the level of physically isolated and identified heteropentamers is feasible with labeled agonists that do not dissociate upon solubilization. This is demonstrated with three neuropeptide Y (NPY) receptors and could apply to many receptors that use large peptidic agonists.

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