Biomedical subjects

S Popov

Publications and source records attributed to S Popov.

At least 19 recordsLinked to original sources

PubMed2006

Optophysiology: depth-resolved probing of retinal physiology with functional ultrahigh-resolution optical coherence tomography.

Noncontact, depth-resolved, optical probing of retinal response to visual stimulation with a <10-microm spatial resolution, achieved by using functional ultrahigh-resolution optical coherence tomography (fUHROCT), is demonstrated in isolated rabbit retinas. The method takes advantage of the fact that physiological changes in dark-adapted retinas caused by light stimulation can result in local variation of the tissue reflectivity. fUHROCT scans were acquired from isolated retinas synchronously with electrical recordings before, during, and after light stimulation. Pronounced stimulus-related changes in the retinal reflectivity profile were observed in the inner/outer segments of the photoreceptor layer and the plexiform layers. Control experiments (e.g., dark adaptation vs. light stimulation), pharmacological inhibition of photoreceptor function, and synaptic transmission to the inner retina confirmed that the origin of the observed optical changes is the altered physiological state of the retina evoked by the light stimulus. We have demonstrated that fUHROCT allows for simultaneous, noninvasive probing of both retinal morphology and function, which could significantly improve the early diagnosis of various ophthalmic pathologies and could lead to better understanding of pathogenesis.

Animals↗

PubMed2003

Galanthamine distribution in Bulgarian Galanthus spp.

Sixteen populations of Galanthus elwesii Hook.fil and five populations of Galanthus nivalis L. growing in Bulgaria were investigated for the presence of galanthamine by TLC and GC-MS. Between 3 and 11 alkaloids were detected by TLC in the total alkaloid fractions. Galanthamine was found in 2 populations of G. elwesii.

Bulgaria↗

PubMed2001

Determination of the contact energies between a regulator of G protein signaling and G protein subunits and phospholipase C beta 1.

Cell signaling proteins may form functional complexes that are capable of rapid signal turnover. These contacts may be stabilized by either scaffolding proteins or multiple interactions between members of the complex. In this study, we have determined the affinities between a regulator of G protein signaling protein, RGS4, and three members of the G protein-phospholipase Cbeta (PLC-beta) signaling cascade which may allow for rapid deactivation of intracellular Ca(2+) release and activation of protein kinase C. Specifically, using fluorescence methods, we have determined the interaction energies between the RGS4, PLC-beta, G-betagamma, and both deactivated (GDP-bound) and activated (GTPgammaS-bound) Galpha(q). We find that RGS4 not only binds to activated Galpha(q), as predicted, but also to Gbetagamma and PLCbeta(1). These interactions occur through protein-protein contacts since the intrinsic membrane affinity of RGS4 was found to be very weak in the absence of the protein partner PLCbeta(1) or a lipid regulator, phosphatidylinositol-3,4,5 trisphosphate. Ternary complexes between Galpha(q), Gbetagamma and phospholipase Cbeta(1) will form, but only at relatively high protein concentrations. We propose that these interactions allow RGS4 to remain anchored to the signaling complex even in the quiescent state and allow rapid transfer to activated Galpha(q) to shut down the signal. Comparison of the relative affinities between these interacting proteins will ultimately allow us to determine whether certain complexes can form and where signals will be directed.

Animals↗

PubMed2001

Non-destructive NIR-FT-Raman analyses in practice. Part I. Analyses of plants and historic textiles.

Non-destructive analysis of natural substances in plants as well as of old dyed textiles by Raman spectroscopy has not been possible using conventional techniques. Exciting lines from the visible part of the spectrum produced photochemical and thermal decomposition of the objects as well as strong fluorescence. Using Nd:YAG laser excitation at 1,064 nm together with a special sample arrangement and interferometric recording, various polyacetylenes in Aethusa cynapium and in chamomile (Chamomilla recutita) and the main valuable substances in gentian species (Gentiana lutea and G. punctata), curcuma roots (Curcuma longa), cinnamon (Cinnamomum zeylanicum), fennel (Foeniculum vulgare), clove (Caryophyllus aromaticus), and ginger (Zingiber officinale) were analyzed non-destructively and discussed in comparison with the corresponding pure standard compounds. We further analyzed non-destructively the FT Raman spectra of collections of historical textiles and lakes used for dyeing. It is possible to distinguish the main dye component non-destructively by using Raman bands.

Biological Factors↗

PubMed2001

Development in a primary cell culture of the marine sponge Ircinia muscarum and analysis of the polar compounds.

We have established a primary cell culture of the marine demosponge Ircinia muscarum. The culture was started from a cell suspension obtained by a combination of mechanical chemical means. Microbial contamination was controlled by the use of a pool of antibiotics. Optical density, rather than hemocytometer count, is suggested to monitor the cellular growth. Analysis of the chemical composition of I. muscarum cells revealed absence of sterols, showing that the cells were unable to biosynthesize sterols. When the medium was supplemented with cholesterol an increase of about 70% in the number of cells was observed. These results suggest that the classic mammalian nutrient medium was not satisfactory for I. muscarum cell growth, and sterols were needed to satisfy the membrane requirements.

Journal Article↗

PubMed2001

RGS proteins provide biochemical control of agonist-evoked [Ca2+]i oscillations.

Agonist-evoked [Ca2+]i oscillations have been considered a biophysical phenomenon reflecting the regulation of the IP3 receptor by [Ca2+]i. Here we show that [Ca2+]i oscillations are a biochemical phenomenon emanating from regulation of Ca2+ signaling by the regulators of G protein signaling (RGS) proteins. [Ca2+]i oscillations evoked by G protein-coupled receptors require the action of RGS proteins. Inhibition of endogenous RGS protein action disrupted agonist-evoked [Ca2+]i oscillations by a stepwise conversion to a sustained response. Based on these findings and the effect of mutant RGS proteins and anti-RGS protein antibodies on Ca2+ signaling, we propose that RGS proteins within the G protein-coupled receptor complexes provide a biochemical control of [Ca2+]i oscillations.

Amino Acid Substitution↗

PubMed2001

Iridoid and phenylethanoid glycosides from Phlomis longifolia var. longifolia.

From the aerial parts of Phlomis longifolia var. longifolia four iridoid glucosides, shanzhiside methyl ester (1), 5-deoxypulchelloside I (2), lamalbide (3), phlomiol (4) and three phenylethanoid glycosides, verbascoside (5), forsythoside B (6), leucosceptoside A (7) along with the caffeic acid ester, chlorogenic acid (8) were isolated. The structures of the isolated compounds were established by spectroscopic (UV, IR, 1D- and 2D-NMR, FABMS) and chemical evidence. The structure elucidation of the iridoid compounds 2 and 3 are discussed in detail.

Chromatography, Liquid↗

PubMed2000

Heat-shock protein 70 can replace viral protein R of HIV-1 during nuclear import of the viral preintegration complex.

Heat-shock proteins (Hsp's) are a family of molecular chaperones that contribute to protection from environmental stress. In this report, we demonstrate that a member of this family, Hsp70, facilitates nuclear import of HIV-1 preintegration complexes (PICs). The mechanism of this activity appears to be similar to the one used by Vpr, an HIV-1 protein regulating viral nuclear import and replication in macrophages. Indeed Hsp70 stimulated binding of HIV-1 matrix antigen to GST-karyopherin alpha fusion protein and rescued nuclear import of a Vpr-defective HIV-1 strain in vitro. Binding studies with truncated forms of GST-karyopherin alpha demonstrated that both Vpr and Hsp70 bind to a region in the amino-terminal part of the karyopherin alpha molecule. This region appears to be distinct from the binding sites for two other karyopherin alpha cargoes, basic-type NLS-containing proteins and transcription factor STAT-1. Vpr competed with Hsp70 for binding to karyopherin alpha. These results suggest the presence of a novel regulatory site on karyopherin alpha which is used by Hsp70 and Vpr to stimulate interaction between the HIV-1 PIC and karyopherin alpha and thus promote viral nuclear import.

Antigens, Polyomavirus Transforming↗

PubMed2000

Two nuclear localization signals in the HIV-1 matrix protein regulate nuclear import of the HIV-1 pre-integration complex.

Replication of HIV-1 in non-dividing and slowly proliferating cell populations depends on active import of the viral pre-integration complex (PIC) into the cell nucleus. While it is commonly accepted that this process is mediated by an interaction between the HIV-1 PIC and the cellular nuclear import machinery, controversial results have been reported concerning the mechanisms of this interaction. Here, we demonstrate that a recently identified nuclear localization signal within the HIV-1 matrix protein (MA), MA NLS-2, together with previously described MA NLS-1, mediates nuclear import of the HIV-1 PIC. Inactivation of both MA NLSs precluded nuclear translocation of MA and rendered the virus defective in nuclear import and replication in non-dividing macrophage cultures, even when functional Vpr and integrase (IN), two more viral proteins implicated in HIV-1 nuclear import, were present. Taken together, these results indicate that Vpr does not function as an independent nuclear import factor and demonstrate that HIV-1 MA, by virtue of its two nuclear localization signals, regulates HIV-1 nuclear import.

Amino Acid Sequence↗

PubMed2000

[Hidden intracardiac conduction disturbances and their spontaneous course in patients with progressive muscular dystrophy].

In patients with progressive muscular dystrophy (PMD) invasive electrophysiologic studies can detect hidden intracardiac conduction disturbances. The aim of this study was a long-term follow-up of these patients. Twelve consecutive patients (9 m, 3 f, age 28 +/- 4 yrs) without cardiac symptoms and with normal echocardiographic findings were included in the study. They suffered from different stages of PMD type Erb (n = 4), Becker-Kiener (n = 4), Duchenne (n = 2) and Landouzy-Déjerine (n = 2). At the beginning of the study all patients underwent an invasive electrophysiologic study (EPS). The follow-up of 5.5 yrs included regular clinical visits, ECGs, and Holter recordings (every 3 months) as well as an echocardiography every 6 months. In 4 patients the EPS revealed a hidden interatrial conduction disturbance (AHRS-ACS 120 +/- 18 ms), and in 10 pts an infrahisian conduction disturbance was found (HV max. 156 +/- 4 ms). Conduction defects were seen independently from the type of PMD and the stage of the disease. During the follow-up the initially hidden interatrial conduction disturbance became evident in the surface ECG in 2 of 4 pts. One of them developed paroxysmal atrial fibrillation. Five of 10 pts with an initially hidden infrahisian conduction disturbance developed an AV block grade I-III and in one case additionally a bundle branch block. Four of these pts--whose PMD showed progression or who developed congestive cardiomyopathy--needed pacemaker implantation because of a first-degree AV block + bifascicular bundle branch block (n = 1), a Mobitz II second-degree AV block (n = 1) or a third-degree AV block (n = 2). None of the pts with normal findings at the EPS showed abnormal p-waves, an AV block, or an intraventricular conduction disturbance during the follow-up. We conclude that intracardiac conduction disturbances, especially infrahisian defects including high-degree AV blocks, are a common finding in pts with PMD. Therefore a regular cardiological screening including an ECG and a Holter recording is reasonable in these patients.

Adolescent↗

PubMed2000

Triterpene saponins and iridoid glucosides from galium rivale.

Three new glycosides of the oleanene-type triterpenes, rivalosides C-E (1-3), along with three known triterpene saponins, momordin IIb (4) and rivalosides A-B (5-6), and five known iridoid glucosides: monotropein, scandoside, deacetylasperulosidic acid, geniposidic acid and asperulosidic acid, were isolated from aerial parts of Galium rivale. The structures of the new compounds were elucidated by spectral methods and chemical means as 2alpha-acetoxy-3alpha, 19alpha-dihydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1--> 6)-beta-D-glucopyranoside, 2alpha,3alpha, 19alpha-trihydroxy-olean- 12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranoside and 3-O-beta-D-glucuronopyranosyl-24-hydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranoside, for rivalosides C-E, respectively. The taxonomic significance of the rivalosides in G. rivale was discussed.

Glucosides↗

PubMed2000

Metabolites from a marine bacterium Pseudomonas/Alteromonas, associated with the sponge Dysidea fragilis.

The lipophylic extract from a Black Sea bacterium, associated with the sponge Dysidea fragilis, was investigated. Saturated hydrocarbons and fatty acids of the lipids were identified. The concentrations of the polycyclic compounds appeared to be negligible. The main components appeared to be phosphatidyl ethanolamine, followed by phosphatidyl serine. The first was investigated by FAB mass spectrometry and a series of molecular species partially identified.

Alteromonas↗

PubMed2000

Plasma membrane recycling and flow in growing neurites.

Axonal growth requires insertion of newly synthesized membrane components into the plasmalemma. Imbalance between exocytotic membrane addition and endocytic retrieval at specific axonal sites may lead to the bulk plasma membrane flow along the axon and, thus, contribute to the renewal of plasma membrane components. By using fluorescent lipid analogs incorporated into the plasma membrane, we determined the sites of membrane internalization in growing Xenopus embryo neurons. Vectorial traffic of endocytic membranes from the distal axon to the cell body was observed, suggesting bulk retrieval of plasma membrane at the growth cone. No long-range axonal transport of membrane material internalized at the cell body or along the axon was detected. In addition, we measured the rate of plasma membrane flow in Xenopus neurites. Axonal plasma membrane was found to flow anterogradely with the rate equal to approximately 30% of the rate of neurite elongation. Our results suggest that the "growth from the tip" pattern of neurite elongation may coexist with transport of new membrane components along plasmalemma by anterograde membrane flow.

Animals↗

PubMed2000

Regulators of G-protein signaling in receptor complexes.

G protein signaling pathways regulate heart development and adult cardiac function. G protein activity is controlled by the interplay between receptor-catalyzed activation and the inhibitory regulators of G protein signaling (RGS) proteins. Most RGS proteins are GTPase accelerating proteins (GAPs) for Gi and Gq class G protein alpha subunits, and thereby terminate signaling. However, RGS proteins also provide scaffolding properties to help assemble or maintain signaling complexes. Thus, RGS proteins are kinetic regulators that may sharpen both signal activation and termination. The five subfamilies of mammalian RGS proteins contain a characteristic RGS domain and distinct flanking domains that convey lipid and/or protein interactions within receptor complexes. The RGS domain provides GAP activity and additional interactions with the receptor complex. Distantly related RGS-like (RGL) proteins provide other regulatory and effector functions in G protein signaling pathways. RGS and RGL proteins provide exciting new therapeutic targets to combat cardiovascular diseases.

Animals↗

PubMed2000

Rivalosides A and B, two 19-Oxo triterpenoid saponins from Galium rivale.

Two new oleanene-type triterpene glycosides, rivaloside A (2alpha-acetoxy-3alpha-hydroxy-19-oxo-olean-12-en-28-o ic acid 28-O-beta-glucopyranosyl-(1-->6)-beta-D-glucopyranoside) (1) and rivaloside B (2alpha,3alpha-dihydroxy-19-oxo-olean-12-en-28-oic acid 28-O-beta-glucopyranosyl-(1-->6)-beta-D-glucopyranoside) (2), were isolated from aerial parts of Galium rivale. The structures were determined on the basis of spectroscopic data and chemical transformations. Under alkaline or acid hydrolysis, rivalosides A and B undergo allylic rearrangement with migration of the double bond. These compounds are the first representatives of 19-oxo substituted oleanenes, and they seem to be promising as taxonomic markers for G. rivale.

Carbohydrate Conformation↗

PubMed2000

A beta-amino acid containing tripeptide from a Pseudomonas-alteromonas bacterium associated with a black sea sponge.

A novel tripeptide, 1, was isolated from the extracellular extract of a Pseudomonas-Alteromonas bacterium that was associated with the Black Sea sponge Dysidea fragilis. Compound 1 contains the novel beta-aminopimelic acid described for the first time from a natural product. The structure of 1 is suggested on the basis of the analysis of spectroscopic data and chemical degradation.

Alteromonas↗

PubMed1999

Palmitoylation of a conserved cysteine in the regulator of G protein signaling (RGS) domain modulates the GTPase-activating activity of RGS4 and RGS10.

RGS4 and RGS10 expressed in Sf9 cells are palmitoylated at a conserved Cys residue (Cys(95) in RGS4, Cys(66) in RGS10) in the regulator of G protein signaling (RGS) domain that is also autopalmitoylated when the purified proteins are incubated with palmitoyl-CoA. RGS4 also autopalmitoylates at a previously identified cellular palmitoylation site, either Cys(2) or Cys(12). The C2A/C12A mutation essentially eliminates both autopalmitoylation and cellular [(3)H]palmitate labeling of Cys(95). Membrane-bound RGS4 is palmitoylated both at Cys(95) and Cys(2/12), but cytosolic RGS4 is not palmitoylated. RGS4 and RGS10 are GTPase-activating proteins (GAPs) for the G(i) and G(q) families of G proteins. Palmitoylation of Cys(95) on RGS4 or Cys(66) on RGS10 inhibits GAP activity 80-100% toward either Galpha(i) or Galpha(z) in a single-turnover, solution-based assay. In contrast, when GAP activity was assayed as acceleration of steady-state GTPase in receptor-G protein proteoliposomes, palmitoylation of RGS10 potentiated GAP activity >/=20-fold. Palmitoylation near the N terminus of C95V RGS4 did not alter GAP activity toward soluble Galpha(z) and increased G(z) GAP activity about 2-fold in the vesicle-based assay. Dual palmitoylation of wild-type RGS4 remained inhibitory. RGS protein palmitoylation is thus multi-site, complex in its control, and either inhibitory or stimulatory depending on the RGS protein and its sites of palmitoylation.

Animals↗

PubMed1999

Alternate coupling of receptors to Gs and Gi in pancreatic and submandibular gland cells.

Many Gs-coupled receptors can activate both cAMP and Ca2+ signaling pathways. Three mechanisms for dual activation have been proposed. One is receptor coupling to both Gs and G15 (a Gq class heterotrimeric G protein) to initiate independent signaling cascades that elevate intracellular levels of cAMP and Ca+2, respectively. The other two mechanisms involve cAMP-dependent protein kinase-mediated activation of phospholipase Cbeta either directly or by switching receptor coupling from Gs to Gi. These mechanisms were primarily inferred from studies with transfected cell lines. In native cells we found that two Gs-coupled receptors (the vasoactive intestinal peptide and beta-adrenergic receptors) in pancreatic acinar and submandibular gland duct cells, respectively, evoke a Ca2+ signal by a mechanism involving both Gs and Gi. This inference was based on the inhibitory action of antibodies specific for Galphas, Galphai, and phosphatidylinositol 4,5-bisphosphate, pertussis toxin, RGS4, a fragment of beta-adrenergic receptor kinase and inhibitors of cAMP-dependent protein kinase. By contrast, Ca2+ signaling evoked by Gs-coupled receptor agonists was not blocked by Gq class-specific antibodies and was unaffected in Galpha15 -/- knockout mice. We conclude that sequential activation of Gs and Gi, mediated by cAMP-dependent protein kinase, may represent a general mechanism in native cells for dual stimulation of signaling pathways by Gs-coupled receptors.

Animals↗