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Biomedical subjects

F Conti

Publications and source records attributed to F Conti.

At least 73 records · Page 4Linked to original sources
PubMed1985

NMR imaging in transient cerebral ischemia.

NMR has proved useful in the detection of Acute Cerebrovascular Disorders (ACVD), providing information related either to the tissue signal intensity and relaxation times, or to the morphological aspects of cerebral structures. Eighteen patients suffering from ischemic Acute Cerebrovascular Disorders were studied. A comparison between NMR imaging and CT scan was performed. Ischemic lesions, presence of edema, presence of reactive gliosis and anatomical vascular anomalies were found.

Acute Disease↗
PubMed1984

Detection of phospholipid phase separation. A multifrequency phase fluorimetry study of 1,6-diphenyl-1,3,5-hexatriene fluorescence.

Using multifrequency phase and modulation fluorometry and a nonlinear least-squares analysis of lifetime data, we were able to determine the complex decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) in synthetic phospholipid bilayers. Our results showed a monoexponential decay of DPH in the pure isotropic solvents studied, over a wide temperature range, and a double-exponential decay of DPH in phospholipids, both above and below the transition. During the transition, and in mixed-phase phospholipids, a three-component analysis was successfully accomplished, and the pre-exponential factors of the two main components have been shown to be quantitatively representative of the gel and liquid-crystalline phases of the bilayer. The fractional intensity of the shorter lifetime component depends on the modalities of the sample preparation. The factors affecting this component are discussed. From the DPH fluorescence lifetime and from the anisotropy data in L-alpha-dimyristoyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidyl choline mixtures, a phase diagram was independently constructed. Conclusions about the sensitivity and the partition of the probe between gel and the liquid-crystalline phases of the bilayer are derived. Lifetime experiments on DPH in a L-alpha-dilauroyl-phosphatidylcholine/L-alpha-dipalmitoyl-phosphatidylch oline mixture suggested a general method for the determination and quantitation of the two different phases in the bilayer.

Dimyristoylphosphatidylcholine↗
PubMed1984

Fluorescence studies using synchrotron radiation on normal and differentiated cells labeled with parinaric acids.

Changes in membrane properties during the differentiation process in K562 cells have been investigated. A decrease of lectin-induced agglutination has been detected. The agglutination assay revealed to be an early and sensitive test to monitor the induced differentiation of the K562 cells. Naturally occurring fluorescent fatty acids (cis- and trans-parinaric acids) and the recently developed multifrequency phase and modulation technique were used to study cell membrane properties. Changes in fluorescence lifetime and polarization are clearly associated with cell differentiation, suggesting the involvement of the cellular plasma membrane in the differentiation process.

Cell Aggregation↗
PubMed1984

Drug-membrane interactions: silymarin, silibyn and microsomal membranes.

Silymarin and silibyn are extracted from the seeds of Silybum marianum and used as a liver protectant because of their free radical scavenging. When incorporated into rabbit liver microsomes they cause a small decrease in the flourescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) but not of 1-anilinononaphthalene-8-sulphonic acid (ANS), incorporated into the membranes. They do, however, reduce the fluorescence intensity of incorporated ANS without changing the wavelength of maximum intensity. These observations suggest that the drugs are incorporated into the hydrophobic-hydrophilic interface of the microsomal bilayer and perturb the structure by influencing the packing of the acyl chains.

Anilino Naphthalenesulfonates↗
PubMed1984

Topography and receptive field organization of the body midline representation in the ventrobasal complex of the cat.

The topography and receptive field (RF) organization of neurones in the trunk zone of the thalamic ventrobasal complex (VB) projecting to the homologous zone of the ipsilateral first somatosensory area (SI) were studied in the cat by performing experiments of retrograde neuronal tracing and microelectrode recording. Punctate cortical injections of small amounts of either horseradish peroxidase or fluorescent tracers (Evans Blue, Nuclear Yellow and Fast Blue) retrogradely labelled cell aggregates lying in the dorsal half of a VB region interposed between subnucleus VPL1 and VPLm. Aggregates of labelled cells were narrow in dorsoventral and mediolateral extent and elongated rostrocaudally. The distribution of VB cells projecting to the cortical subareas representing the dorsal midline, lateral trunk and ventral midline of the body in area SI, was established by injecting a different fluorescent marker into a physiologically defined site in each subarea. These injections resulted in labelling of three different cell aggregates located in topographically distinct regions of the VB trunk zone. Each aggregate of labelled cells only projected to one cortical subarea. Microelectrode analysis of cell populations of the VB trunk zone showed that neurones lying in regions projecting to dorsal and ventral midline zones of area SI had bilateral RFs, straddling the dorsal and the ventral midline of the body respectively. Neurones lying in the region projecting to the lateral trunk representation of area SI had contralateral RFs located on the lateral surface of the trunk. The results suggest that the detailed topography of the trunk map in the area SI and the bilaterality of the cortical representation of the body midlines, described in previous experiments, is imposed by the thalamocortical input from the VB.

Animals↗
PubMed1984

Extrinsic charge movement in the squid axon membrane. Effect of pressure and temperature.

The absorption of the lipophilic anions dipicrylamine (DPA-) and tetraphenylborate (TPhB-) by the lipid matrix of the squid axon membrane, and the kinetics of their translocation, were studied by the charge pulse relaxation technique. The axons were treated with tetrodotoxin (TTX) and 4-aminopyridine to block the ionic currents responsible for nerve excitation. At high enough concentrations of absorbed ions (approximately 10(-12) mol/cm2) the membrane voltage relaxation following a brief current pulse consisted mainly of two exponential components, whose time constants and relative amplitudes were used for estimating the translocation rate constant, K, and the density of absorbed ions, N. These measurements were performed at different hydrostatic pressures in the range 1-100 MPa (approximately 1,000 atm), and at different temperatures in the range 5 degrees C-20 degrees C. Both K and N were found to be little affected by pressure. The pressure dependence of K indicated that the translocation of lipophilic ions across the nerve membrane involves activation volumes of the order of 5 cm3/mol. In all experiments the passive membrane resistance was little affected by pressures up to 80 MPa. However, above 100 MPa it fell dramatically to low values, presumably because of phase separation phenomena between the membrane components. The temperature dependence of K, both for DPa- and TPhB-, implied an activation energy for ion translocation of the order of 60 kJ/mol, close to that measured in artificial lipid bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Pressure dependence of sodium gating currents in the squid giant axon.

Asymmetric displacement currents, Ig, were measured in squid axons at different hydrostatic pressures, P, up to 60 MPa. Potassium and sodium currents were abolished by intracellular Cs+ and TEA+, by extracellular Tetrodotoxin (TTX), and by Na+ substitution with Tris+. The time course of Ig became progressively slower with increasing pressure, and the amplitude decreased. With appropriate scaling in time and amplitude, Ig records at any given P could be made to superimpose very well with those obtained at atmospheric pressure. The same scaling factors yielded a good superposition of all records obtained for voltage steps to membrane potentials in the range -30 to +42 mV. The ratio between the amplitude and time factors was larger than unity and increased with P, indicating a progressive decrease (up to 35% at 60 MPa) of the total charge displaced, Q, with no significant change in its voltage dependence. The time-scaling factor increased exponentially with P, as expected if all the steps involved in the opening of a sodium channel, and producing a major charge redistribution, have the same activation volume, delta V not equal to g approximately 17 cm3/mol. This value is roughly one-half of that characterizing the pressure dependence of sodium current activation, suggesting that some late, rate-limiting step in the opening of sodium channels has a large activation volume without being accompanied by an easily detected charge movement. Part of the decrease of Q with pressure could be attributed to an increase in sodium inactivation. However, we cannot exclude the possibility that there is a reversible reduction in the number of fast activating sodium channels, similar to the phenomenon that has been reported to occur at low temperatures (Matteson and Armstrong 1982).

Animals↗
PubMed1984

Non-stationary fluctuations of the potassium conductance at the node of ranvier of the frog.

Potassium currents were recorded from voltage-clamped nodes of isolated, myelinated axons of Rana pipiens. Nodes were maintained in a modified Ringer solution containing tetrodotoxin to block sodium current and 47.5 mM-potassium to minimize effects of extracellular potassium accumulation. Voltage protocols included depolarizing pulses lasting a few milliseconds to several seconds. Fluctuations about the ensemble average of the current were characterized in terms of non-stationary variance and autocovariance. The fluctuations had a Gaussian amplitude distribution and were virtually free of contaminations from systematic variations of the membrane current. Corrections for background noise were based on measurements done while potassium current was blocked with tetraethylammonium, and on simulations of extrinsic current fluctuations expected to arise from noise in the actual membrane voltage. The fluctuations were attributed to variations of nodal potassium conductance, since they were absent at the reversal potential of the potassium current and at membrane voltages that do not activate potassium current. Covariances indicated that voltage steps that reversed a macroscopic potassium current also reversed the sign of the fluctuation. Plots of the conductance variance versus the mean potassium conductance were generated from both the activation and deactivation (tail) phases of the potassium currents at various voltages between -80 and +70 mV. When the current was activated by a small depolarization (-50 mV) the trajectories from both phases were indistinguishable and were fitted by the parabola expected for a single population of channels with only one open-channel conductance. Apparent single-channel conductance from the early activation phase averaged 24 pS and was not significantly voltage dependent. In contrast, experiments with large depolarizations (+10 to +70 mV) gave significantly different variance--mean trajectories during activation and deactivation and these trajectories were poorly fitted by parabola. This result indicates that the fluctuations reflect several populations of channels and/or a population of channels that can have several levels of non-zero conductance. Projections of the fluctuation covariance showed long correlations, as well as the rapidly decaying component expected from the activation gating of channels. A slow fluctuation arose at a time slightly later than the rise of potassium current, spanned the entire length of brief depolarizations, and extended up to 880 ms during long depolarizations.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1982

Periaqueductal grey projection to the ventrobasal complex in the cat: an horseradish peroxidase study.

Horseradish peroxidase (HRP) was injected within the thalamic ventrobasal complex of 14 cats. The aim was to ascertain whether the periaqueductal grey matter (PAG) sends fibres to this complex. Retrogradely labelled cells were found within the PAG following HRP delivery either in the nucleus ventralis posterolateralis (VPL) or ventralis posteromedialis (VPM). PAG-VPL projection is only ipsilateral and arises mainly from lateral PAG, PAG-VPM projection is bilateral and originates from latero-ventral regions of the central grey. The hypothesis that PAG might control the activity of ventrobasal nociceptive neurones is proposed.

Afferent Pathways↗
PubMed1981

Reversible electrical breakdown of squid giant axon membrane.

Charge pulse relaxation experiments were performed on squid giant axon. In the low voltage range, the initial voltage across squid axon membrane was a linear function of the injected charge. For voltages of the order of 1 V this relationship between injected charge and voltage across the membrane changes abruptly. Because of a high conductance state caused by these large electric fields the voltage across the membrane cannot be made large enough to exceed a critical value, Vc, defined as the breakdown voltage, Vc has for squid axon membrane a value of 1.1 V at 12 degrees C. During breakdown the specific membrane conductance exceeds 1 S. cm-2. Electrical breakdown produced by charge pulses of few microseconds duration have no influence on the excitability of the squid axon membrane. The resealing process of the membrane is so fast that a depolarizing breakdown is followed by the falling phase of a normal action potential. Thus, membrane voltages close to Vc open the sodium channels in few microseconds, but do not produce a decrease of the time constant of potassium activation large enough to cause the opening of a significant percentage of channels in a time of about 10 mus. It is probable that the reversible electrical breakdown is mainly caused by mechanical instability produced by electrostriction of the membrane (electrochemical model), but the decrease in the Born energy for ion injection into the membrane, accompanying the decrease in membrane thickness, may play also an important role. Because of the high conductance of the membrane during breakdown it seems very likely that this results in pore formation.

Action Potentials↗
PubMed1981

Electron spin resonance of growing normal and virus-transformed cells.

A g = 2.003 ESR signal, attributed to a free radical localized in HeLa cell nuclei and mitochondria but absent in membranes and cytoplasm, has been studied as a function of the culture growth cycle in normal (NRK and 3T3) and virus transformed (NRK/RSV and 3T3/SV40) cells. For both these cell pairs, the signal is higher during the "lag" stage and lower during the "growth" stage. The average specific intensity of the signal in normal cells is about twice that in virus-transformed cells. However, the maximal point of resonance during the lag state is higher in transformed cells than in normal ones. The lag stage in NRK and NRK/RSV cells is much longer than in 3T3 and 3T3/SV40 cells, while the maximal value of the g = 2.003 ESR signal occurs, early in the lag stage of 3T3 and 3T3/SV40 cells and late in the lag stage of NRK and NRK/RSV cells.

Animals↗
PubMed1980

Single channel recordings of K+ currents in squid axons.

Ionic currents from individual K+ channels in squid axon membrane have been recorded. At hyperpolarizing membrane voltages, unit events occur as widely spaced rectangular pulses with short interruptions. The frequency of occurrence of the units increases strongly when the membrane is depolarized.

Animals↗