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Biomedical subjects

D G Mărgineanu

Publications and source records attributed to D G Mărgineanu.

At least 19 recordsLinked to original sources
PubMed1990

Effects of millimolar concentrations of glutaraldehyde on the electrical properties of frog skin.

1. The effects of millimolar concentrations of glutaraldehyde on the electrophysiological properties of the epithelium of frog skin (Rana temporaria) were investigated. We recorded short-circuit current (Isc), transepithelial conductance (Gt) and impedance (Zt), fractional resistance (fRo) and the potential difference across the apical membrane (Vo). We used either Na+ or K+ as major mucosal cations to compare the effects on transepithelial Na+ and K+ currents (INa and IK) and thus on the apical Na+ and K+ permeabilities. 2. At concentrations above 0.005% (w/v) or 0.5 mM, glutaraldehyde irreversibly and completely inhibits both INa and IK within 2-3 h. The initial time courses of the inhibition of transepithelial currents following serosal and mucosal applications of the compound markedly differ. 3. Glutaraldehyde decreased Gt in sulphate Ringer solutions while it augmented Gt severalfold in chloride Ringer solution. 4. Measurements of the transepithelial impedance of tissues incubated with sulphate solutions showed that glutaraldehyde increased the resistances of both apical and basolateral membranes significantly. The capacitance of the apical membrane was augmented, while the basolateral membrane capacitance was drastically decreased. 5. Microelectrode impalements of the granulosum cells showed that glutaraldehyde decreased Vo by more than 40 mV and increased fRo, which reached values around 90%. 6. The role of free amino groups in ion-transporting proteins and the potential non-fixative uses of protein cross-linkers in epithelia are discussed.

Animals↗
PubMed1987

Procaine has opposite effects on passive Na and K permeabilities in frog skin.

Procaine has opposite effects on the active transport of Na+ when applied on the mucosal side of the frog skin [where it produces a stimulation of the short-circuit current (Isc)] or when added on the serosal side (where it produces an inhibition of Isc). In an attempt to reveal and localize the primary effect of procaine on either the apical or latero-basal membranes of the epithelial cells, we have tried to "chemically dissect" both membrane functions with inhibitors and ionophores. When applied on the apical side of the latero-basally depolarized epithelium, 25 mmol/l procaine increases Isc and Voc (transepithelial open-circuit potential), while decreasing the transepithelial resistance. The E1-E2 linearity domain of the I-V curves is narrowed. On the serosal side of the depolarized epithelium, the same concentration of procaine does not affect Isc and Voc (which are already inhibited) but it produces an increase in the transepithelial resistance (Rt). Procaine influence on the passive K+ permeability was studied by using the ionophore nystatin, which is assumed to form channels permeable to K+, when applied on the amiloride blocked apical membrane. In nystatin-treated epithelia, 25 mmol/l procaine on the apical side decreased Isc, Voc and Rt. In parallel experiments during Cl- substitution by SO2-(4), the procaine effects on Isc and Voc are no longer maintained, but transient.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1987

Temperature dependence of the effects of tertiary amines on osmotic hemolysis.

The effects of four tertiary amines (procaine, lidocaine, tetracaine and dibucaine) on the osmotic fragility and the rate of hemolysis of human erythrocytes were investigated in the range between 22-42 degrees C. The temperature dependence of the relative hemolysis indicates the existence of certain critical points in the antihemolytic effect of these substances. The relative rate of hemolysis, which is well known to be a parameter accounting for the fluidity of erythrocyte membrane, decreases with increasing drug concentration, indicating a decrease in membrane fluidity. The amount of drugs actually bound to the erythrocytes increases linearly with the external concentration, as shown by UV-absorption.

Amines↗
PubMed1986

A target theory description of the chemical inactivation of membrane functions.

The basic ideas of target theory (currently employed in radiobiology) are applied to describe the chemical inactivation of any biological function arising from the summation of a large number of identical individual contributions. A general equation giving the fractional survival of a biological activity as a function of the mean number of hits received by each target from the inactivating molecules and on the number of individual targets forming the functional assemblies is established. It properly accommodates phenomena as diverse as the decrease by anesthetics of the compound action potential in nerve trunks, the inhibition by protein cross-linking reagents of the active transport of sodium across epithelia and the killing of bacteria by disinfectants. This approach seems able to extract molecular level information from macroscopic data.

Cell Membrane↗
PubMed1985

Procaine effects on the sodium transport in frog skin.

A study on the influence of procaine on the sodium transport properties in frog skin was carried out. The application of procaine hydrochloride on either the mucosal or the serosal sides of the isolated frog skin has opposite effects. When added to the mucosal compartment, the procaine (as well as two procaine based drugs: Gerovital H3 and Aslavital) biphasically increase the short-circuit current (Isc) with a noticeable "recline" phenomenon, and decrease the slope resistance, as given by the I-V curves. When applied in the serosal compartment, Isc is decreased and the slope resistance of the epithelium is increased. The procaine effect on the apical membranes shows a pronounced dependence on the external sodium concentration. The shift of the E2 inflection point (which indicates the critical intensity of the electric field at which the epithelial conductance changes), with respect to the transepithelial open-circuit potential, shows a rapid and quasi-exponential increase following the application of 25 mM procaine in addition to the different mucosal Na concentrations.

Animals↗
PubMed1984

Glutaraldehyde inhibits the active transport of sodium and the oxygen consumption, while increasing the water diffusional permeability in frog skin.

A detailed investigation of the effects of mild glutaraldehyde (GA) treatments on both active and passive transport properties of isolated frog skin is presented. The active transport of sodium, as expressed by the short-circuit current, is gradually inhibited when GA is present in the Ringer solution on the serosal face of the skin, even at 0.01% (w/v) concentration. The inhibition is roughly exponential, with time constants ranging from 19 min (at 25 degrees C and 0.10% aldehyde), up to 63 min (at 10 degrees C and 0.01% aldehyde). It seems be partly due to (or, at least, is concomitant with) the inhibition by GA of the tissular oxygen consumption. This is reduced to half of the initial value by 0.10% GA. Higher GA concentrations (0.10 to 1.0%) increase with up to 50% the transepithelial diffusional permeability of water, and also produce even more pronounced increments in the diffusional permeabilities for sodium and potassium. All these data are consistent with the image of GA cross-linking between the free amino (and other reactive) groups on the proteins. This probably results in the severe modification of every functional protein aggregate, thus inactivating the transport ATPases, but also causes a stabilization of protein hydrophilic membrane domains making the water and the small ions to penetrate easier. In view of these opposite effects on active and passive transport of ions, the possibility of using GA at concentrations around 0.05% (w/v) to block the active transport through frog skin and other tight epithelia is suggested.

Aldehydes↗
PubMed1982

Glutaraldehyde effect on the osmotic fragility and rate of haemolysis of human erythrocytes: a kinetic study.

The effect of glutaraldehyde treatment on the osmotic fragility and rate of haemolysis of human erythrocytes was studied in the temperature domain 22-42 degrees C at different aldehyde concentrations from 0.010 to 0.040% (w/v). The osmotic fragility linearly decreases at increasing temperatures for all glutaraldehyde concentrations with approximately the same slope as for the untreated erythrocytes. Rather similar effects are produced on the rate of haemolysis. It was not possible to define unique activation energies. The maximal haemolysis becomes smaller after the treatment with increasing concentrations of glutaraldehyde but more erythrocytes are no longer able to tolerate normally non-haemolysing osmotic stretching, this suggesting an artificial "ageing" of erythrocytes. The formation of a membrane protein skeleton as a result of cross-linking is inferred, while the changes in the cytoskeletal spectrin network seem to be less important.

Aldehydes↗
PubMed1981

Kinetics of nerve impulse blocking by protein cross-linking aldehydes. Apparent critical thermal points.

The effect of formaldehyde, crotonaldehyde, butyraldehyde, glutaraldehyde and cinnamaldehyde on the compound action potential of frog sciatic nerve was studied in the temperature domain 20-35 degrees C at various aldehyde concentrations. All these reagents gradually decrease the amplitude of nerve action potential, up to the complete block, the order of effectiveness being: crotonaldehyde greater than cinnamaldehyde greater than butyraldehyde greater than formaldehyde greater than glutaraldehyde. The effect of cinnamaldehyde is almost completely reversible, while all others have irreversible action. The dependence of the blocking time on temperature and concentration is well expressed in all cases by the same empirical equation. This dependence points to the existence of critical temperatures, specific for each aldehyde, at which impulse blocking would be instantaneous, regardless of concentration. These temperatures (obtained by extrapolation) lie between 43 degrees C (for crotonaldehyde) and 57.5 degrees C (for butyraldehyde). The existence of free amino groups within ionic channels, as main sites of aldehyde attack, is inferred.

Action Potentials↗
PubMed1980

Immersion weighing method for recording the flows through macroscopic membranes.

The continuous record of the apparent weight of a membrane-bounded small vessel immersed in a solution of different density as compared to that inside it, offers a cheap and reliable possibility to measure osmotic flows at 10(-5) kg x m-2 x s-1 sensitivity. The method equally applies for diffusional (isotopic) water flows.

Animals↗
PubMed1979

Water compartments in living, glycerinated and fixed skeletal muscles of the frog.

The kinetics of water replacement with heavy water (deuterium oxide) in the gastrocnemius and sartorius muscles of the frog under isotonic conditions, studied both gravimetrically and by infrared photometry, reveals three water compartments: (i) non-exchangeable (approximately 80 ml/kg fresh weight), (ii) slowly exchanging (approximately 500 ml/kg fresh weight), (iii) rapid exchanging--extracellular (approximately 200 ml/kg fresh weight). Exposure to both glycerol and glutaraldehyde increases the permeability coefficients and the amount of rapid exchanging water; glutaraldehyde also increases the amount of non-exchangeable water. Approximately 90% of the water is kept in the tissue only by weak intermolecular forces, the energies of which amount to 1 kcal/mol. The amount of non-exchangeable water is equivalent to about six continuous adsorption layers covering the myofilaments. Approximately 70% of the tissue water appears to be replaced by glutaraldehyde during standard fixation.

Aldehydes↗