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Biomedical subjects

V A Frolov

Publications and source records attributed to V A Frolov.

At least 19 recordsLinked to original sources
PubMed2005

Laser diffraction for standardization of heterogeneous pharmaceutical preparations.

A new quantitative method for standardization of heterogeneous pharmaceutical preparations and their quality control during storage based on laser diffraction is proposed. A series of pharmaceutical dosage forms--suspensions, emulsions, tinctures, decoctions, cell preparations and others, are heterogeneous medicines. In some cases disperse phase can be formed during storage as a result of layering (L1/L2) or precipitation (S/L). Laser diffraction method proposed in this study can be used for standardization and quality control of medicines.

Lasers↗
PubMed2005

Changes in myocardial blood supply during experimental hypertension treated with verapamil in rabbits.

Rabbit hearts were studied at different periods of experimental arterial hypertension and its treatment with verapamil. Morphological study revealed a progressive decrease in the number of capillaries per unit mass during the development of myocardial hypertrophy in hypertensive hearts. In hypertensive animals treated with verapamil the density of capillaries in both ventricles did not decrease, but verapamil injected to intact animals sharply decreased this parameter.

Animals↗
PubMed2005

Blood pressure and contractile function of heart ventricles at the early stages of hypertonic process.

In rabbits, arterial hypertension was characterized by progressive elevation of systolic and diastolic blood pressure. The contractile function of the left ventricle augmented, but its potential working capacity decreased. Opposite changes were observed in the right ventricle. It was hypothesized that the compensatory mechanisms in the right ventricle during arterial hypertension are triggered at the very onset of the pathology, while in the left ventricle they develop later.

Animals↗
PubMed2004

Initial mechanisms of the development of hypertonic heart.

In rabbits, arterial hypertension was simulated according to Goldblatt. One, 2, 4, and 6 weeks after surgery, the hearts of control and experimental animals were extirpated for morphological examination. In semithin sections of the left and right ventricles, morphometry was performed using an Avtandilov grid. Ultrathin sections of these organs were examined under an electron microscope. It was found that the initial signs of myocardial hypertrophy appeared soon after hypertension modeling, and more early in the right ventricle. Activation of apoptosis was noted in cardiomyocytes of both ventricles, and its intensity correlated with the degree of myocardial hypertrophy. It is hypothesized that apoptosis limits the development of hypertrophy in the myocardium.

Animals↗
PubMed2003

Membrane permeability changes at early stages of influenza hemagglutinin-mediated fusion.

While biological membrane fusion is classically defined as the leak-free merger of membranes and contents, leakage is a finding in both experimental and theoretical studies. The fusion stages, if any, that allow membrane permeation are uncharted. In this study we monitored membrane ionic permeability at early stages of fusion mediated by the fusogenic protein influenza hemagglutinin (HA). HAb2 cells, expressing HA on their plasma membrane, fused with human red blood cells, cultured liver cells PLC/PRF/5, or planar phospholipid bilayer membranes. With a probability that depended upon the target membrane, an increase of the electrical conductance of the fusing membranes (leakage) by up to several nS was generally detected. This leakage was recorded at the initial stages of fusion, when fusion pores formed. This leakage usually accompanied the "flickering" stage of the early fusion pore development. As the pore widened, the leakage reduced; concomitantly, the lipid exchange between the fusing membranes accelerated. We conclude that during fusion pore formation, HA locally and temporarily increases the permeability of fusing membranes. Subsequent rearrangement in the fusion complex leads to the resealing of the leaky membranes and enlargement of the pore.

Animals↗
PubMed2003

Experimental study of myocardial collagen during nifedipine therapy of arterial hypertension.

Light and electron microscopy of the left-ventricular myocardium obtained from spontaneously hypertensive SHR rats showed a pronounced increase in collagen content. These changes were more pronounced in animals treated with nifedipine in the mean therapeutic dose for 8 weeks. Collagen accumulated between muscle fibers and often formed perivascular cuffs. Hence, nifedipine promotes the formation of scleroproteins in the myocardium.

Animals↗
PubMed2002

Ultrastructural changes in myocardium of hypertensive rats treated with nifedipine.

Spontaneously hypertensive rats (SHR) with high systolic pressure received calcium antagonist nifedipine in medium therapeutic doses for 2 weeks. Electron microscopy of the myocardium revealed considerable changes in the sarcoplasmic reticulum manifested in dramatic dilation of tubules, destruction of membranes, and appearance of amorphous matter of medium electron density in tubules in animals treated with nifedipine. Since sarcoplasmic reticulum plays an important role in calcium-dependent excitation-contraction coupling, the observed structural changes can underlie the negative inotropic effect of long-term nifedipine therapy.

Animals↗
PubMed2001

Pro-apoptotic cleavage products of Bcl-xL form cytochrome c-conducting pores in pure lipid membranes.

During apoptotic cell death, cells usually release apoptogenic proteins such as cytochrome c from the mitochondrial intermembrane space. If Bcl-2 family proteins induce such release by increasing outer mitochondrial membrane permeability, then the pro-apoptotic, but not anti-apoptotic activity of these proteins should correlate with their permeabilization of membranes to cytochrome c. Here, we tested this hypothesis using pro-survival full-length Bcl-x(L) and pro-death Bcl-x(L) cleavage products (DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L)). Unlike Bcl-x(L), DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L) caused the release of cytochrome c from mitochondria in vivo and in vitro. Recombinant DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), as well as Bcl-x(L), cleaved in situ by caspase 3-possessed intrinsic pore-forming activity as demonstrated by their ability to efficiently permeabilize pure lipid vesicles. Furthermore, only DeltaN61Bcl-x(L) and DeltaN76Bcl-x(L), but not Bcl-x(L), formed pores large enough to release cytochrome c and to destabilize planar lipid bilayer membranes through reduction of pore line tension. Because Bcl-x(L) and its C-terminal cleavage products bound similarly to lipid membranes and formed oligomers of the same size, neither lipid affinity nor protein-protein interactions appear to be solely responsible for the increased membrane-perturbing activity elicited by Bcl-x(L) cleavage. Taken together, these data are consistent with the hypothesis that Bax-like proteins oligomerize to form lipid-containing pores in the outer mitochondrial membrane, thereby releasing intermembrane apoptogenic factors into the cytosol.

Animals↗
PubMed2001

Voltage-induced nonconductive pre-pores and metastable single pores in unmodified planar lipid bilayer.

Electric fields promote pore formation in both biological and model membranes. We clamped unmodified planar bilayers at 150-550 mV to monitor transient single pores for a long period of time. We observed fast transitions between different conductance levels reflecting opening and closing of metastable lipid pores. Although mean lifetime of the pores was 3 +/- 0.8 ms (250 mV), some pores remained open for up to approximately 1 s. The mean amplitude of conductance fluctuations (approximately 500 pS) was independent of voltage and close for bilayers of different area (40,000 and 10 microm(2)), indicating the local nature of the conductive defects. The distribution of pore conductance was rather broad (dispersion of approximately 250 pS). Based on the conductance value and its dependence of the ion size, the radius of the average pore was estimated as approximately 1 nm. Short bursts of conductance spikes (opening and closing of pores) were often separated by periods of background conductance. Within the same burst the conductance between spikes was indistinguishable from the background. The mean time interval between spikes in the burst was much smaller than that between adjacent bursts. These data indicate that opening and closing of lipidic pores proceed through some electrically invisible (silent) pre-pores. Similar pre-pore defects and metastable conductive pores might be involved in remodeling of cell membranes in different biologically relevant processes.

Electrophysiology↗
PubMed2001

Possible mechanism of regression of myocardial hypertrophy.

Structure of the myocardium was studied in rabbits with renovascular hypertension during the development of myocardial hypertrophy and its regression under the effect of beta-adrenoceptor antagonist lopressor. Myocardial hypertrophy was associated with ultrastructural changes in cardiomyocytes, while lopressor therapy led to their regression and normalization of cardiomyocyte ultrastructure. Regression of hypertrophic changes was accompanied by a marked increase in the number of extracellular nuclei, which indicated enhanced apoptosis of cardiomyocytes.

Adrenergic beta-Antagonists↗
PubMed2001

Effects of transmembrane gradients of bicarbonate and ammonium on junctional and nonjunctional membrane conductances in BHK cells.

Weak acids are efficient blockers of gap-junctional conductance. It is generally accepted that intracellular acidification produced by weak acids fully accounts for the gap-junctional uncoupling. Protonation of the cytoplasmic portions of the channel-forming protein connexin is thought to lead to the conformational changes switching the channel from the open into the closed state. If this is the only mechanism of the weak-acid induced uncoupling, then the correlation between junctional conductance (Gj) and intracellular pH (pHin) should not depend on the means of intracellular acidification. We compared the responses of junctional conductance in BHK cells measured in double whole-cell experiments to the applied transmembrane concentration gradients of bicarbonate or ammonium. These treatments were to lower pHin in a predictable way according to the equations: pHin = pHout -lg[[HCO3]out/HCO3-]in) or pHin = PHout - lg[[NH4+]in[NH4+out), respectively. We found that the behavior of Gj depended on the substance used. At a 500-fold bicarbonate gradient (calculated pHin approximately 4.8) the cells remained coupled, while a 100- or 10-fold gradient of ammonium imposing pHin approximately 6.1 produced fast uncoupling. The responses of junctional conductance were often accompanied or preceded by changes of non-junctional membrane conductance. We suggest that the mechanisms of the weak acid/base-induced channel gating may contain an additional "lipophilic" component due to the presence of the non-dissociated form of the acid/base in cell membrane.

Animals↗
PubMed2000

Multiple local contact sites are induced by GPI-linked influenza hemagglutinin during hemifusion and flickering pore formation.

Membrane fusion intermediates induced by the glycosylphosphatidylinositol-linked ectodomain of influenza hemagglutinin (GPI-HA) were investigated by rapid freeze, freeze-substitution, thin section electron microscopy, and with simultaneous recordings of whole-cell admittance and fluorescence. Upon triggering, the previously separated membranes developed numerous hourglass shaped points of membrane contact (approximately 10-130 nm waist) when viewed by electron microscopy. Stereo pairs showed close membrane contact at peaks of complementary protrusions, arising from each membrane. With HA, there were fewer contacts, but wide fusion pores. Physiological measurements showed fast lipid dye mixing between cells after acidification, and either fusion pore formation or the lack thereof (true hemifusion). For the earliest pores, a similar conductance distribution and frequency of flickering pores were detected for both HA and GPI-HA. For GPI-HA, lipid mixing was detected prior to, during, or after pore opening, whereas for HA, lipid mixing is seen only after pore opening. Our findings are consistent with a pathway wherein conformational changes in the ectodomain of HA pull membranes towards each other to form a contact site, then hemifusion and pore formation initiate in a small percentage of these contact sites. Finally, the transmembrane domain of HA is needed to complete membrane fusion for macromolecular content mixing.

Animals↗
PubMed2000

Hemagglutinin-induced fusion of HAb2 and PLC cells: dynamics of fusion pore conductance.

Infection of cells with influenza virus is mediated by the virus envelope protein hemagglutinin (HA) which induces fusion of viral and target membranes. Earlier we showed using fluorescent microscopy that HAb2 cells expressing HA on their plasma membranes fused with PLC cells when pH of the external medium was decreased to -5. In the present work we used double whole-cell recording to monitor the intercellular conductance in HAb2/PLC cell pairs during fusion. In approximately 40% of cell pairs the pH drop induced the intercellular conductance, which we interpret as the formation of a fusion pore. The following stages of the conductance growth were distinguished: initial fluctuations near zero (flicker), a subsequent slow increase up to 1-4 nS and a final rapid increase up to 10-100 nS (complete fusion). The first detectable intercellular conductance change (opening of a fusion pore) was accompanied by an increase in the conductances of both HAb2 and PLC cell membrane. This observation suggests that the early pore complex should be leaky. The dynamics of the intercellular conductance appeared to depend upon the voltage difference between the fusing HAb2 and PLC cells: voltages higher than 40 mV facilitated the conductance growth.

Cell Fusion↗
PubMed2000

Fusion of a single influenza virion particle with BLM.

One of the key stages of cell infection with influenza virus is the enveloped virus fusion with the cell endosome membrane. To study fusion of single fluorescently-labeled influenza virions with a model bilayer membrane (BLM), a special model system was developed. A small patch of BLM with several adsorbed virions was localized upon a contact with a glass micropipette. Low pH of solution inside the pipette triggered fusion that could be registered by a change in the conductance and integral fluorescence of the BLM patch. It has been shown that the fusion initiation is followed by an increase of fluorescence signal due to the probe redistribution from the virus membrane to the BLM fragment. The increase in fluorescence was accompanied by changes in conductance. Usually, from two to five periods of the channel activity were observed, each of which probably corresponded to fusion of a single virion. It has been found that electric activity was completely inhibited by amantadine known as a blocking agent of M2 channels. This allows one to suggest that the observed changes in conductance are connected with the activity of M2 channels in the virus membrane, whose electric accessibility was the result of fusion of single virions with BLM.

Adsorption↗