Biomedical subjects

C Usai

Publications and source records attributed to C Usai.

31 records · Page 2Linked to original sources

PubMed1995

Pharmacological types of calcium channels and their modulation by baclofen in cerebellar granules.

Voltage-dependent calcium currents were measured by whole-cell recording technique in cultured cerebellar granule neurons from 8 d old rats, in 10 mM BaCl2 and with a holding potential of -80 mV. A saturating dose (10 microM) of the dihydropyridine nimodipine reversibly inhibited the maximum current by 25% and the dose dependence showed IC50 close to 50 nM. omega-Conotoxin GVIA (cgtx, 5 microM) and omega-agatoxin IVA (agatx, 200 nM) irreversibly inhibited the current by 17% and by 47%, respectively. The effect of nimodipine was additive with that of the toxins. The GABAB agonist (+/-)baclofen, or (-)baclofen (100 microM), reduced the calcium current by 30 +/- 5%, with a IC50 4 microM. The effect was mediated by a pertussis toxin-sensitive G-protein. In cells treated with cgtx during the experiment or preincubated with the toxin for 30 min, the effect of baclofen was significantly reduced. However, the action of baclofen was not confined to cgtx-sensitive channels: application of nimodipine or agatx resulted in a 50% reduction of the baclofen effect as well. In contrast, baclofen inhibited approximately the same amount of current both before and after the increase caused by the dihydropyridine agonist BayK 8644 and did not modify the slow BayK-induced tail current. These results indicate (1) the modulation through GABAB receptors does not clearly discriminate between pharmacologically distinct calcium channels and (2) L-type calcium channels represent an heterogeneous population in these neurons.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1994

Extracellular pancuronium affects sodium current in chick embryo sensory neurones.

1. The action of pancuronium on transmembrane sodium conductance was investigated in dorsal root ganglion neurones of chick embryos. The Na+ current was measured by use of the patch-clamp technique in whole-cell configuration. 2. Externally perfused pancuronium (50 microM to 1 mM) reversibly inhibited the current by a fast mechanism of action. Inhibition was concentration-dependent (with a half-effective dose of 170 microM) but not voltage-dependent. 3. The activation and inactivation kinetics of the Na+ current were estimated in pancuronium and in control solution by fitting experimental data with a Hodgkin-Huxley theoretical model. 4. The activation time constant tau m, at negative membrane voltages, was larger in the presence of pancuronium than in the control. In contrast, the inactivation time constant tau h was smaller during drug perfusion at membrane voltages < -10 mV. The steady-state inactivation h infinity was not affected by pancuronium. 5. These results suggest that pancuronium may reduce the sodium current by interacting with the sodium channels in both the resting and open states.

Animals↗

PubMed1994

The general anesthetic propofol inhibits transmembrane calcium current in chick sensory neurons.

The action of propofol on voltage-gated calcium channels was investigated in cultured dorsal root ganglion neurons from chick embryos. The Ca2+ current was measured by using the patch-clamp technique in whole cell configuration. Low-voltage-activated (LVA) and high-voltage-activated (HVA) Ca2+ currents were selected by means of appropriate stimulation protocols. Propofol (0.3 mM) inhibited the LVA T-type current by 80% (P < 0.001). The same concentration of propofol reduced the HVA Ca2+ current with a high variability (10%-75%). The inactivation time constant of the HVA current was also shortened to 50% by propofol. omega-Conotoxin and nifedipine were used to discriminate between the HVA N- and L-type current components. Only the L-type component was strongly depressed (75%) by propofol (P < 0.001); different effects on the HVA current might, therefore, reflect different percentages of L- and N-type channels in neurons. We conclude that propofol inhibits the T-type and L-type components of the Ca2+ current. This inhibition may play a role in the cardiovascular side effects clinically observed.

Animals↗

PubMed1991

Two systems of branching axons in monkey's retina.

Several monkey retinae were stained, by using the reduced silver technique, in order to analyse long-distance intraretinal connections. Long, bifurcating processes covering very large areas were identified. Morphological investigation of these processes suggest that they are members of two different systems of branching axons. The first population of these processes originates as axon collaterals from cell in the ganglion cell layer. These cells have a relatively large, elongated soma and straight, sparsely branching dendrites, stratified in the vitreal half of the inner plexiform layer. The main axon (0.6 microns average diameter) passes along the optic fibre bundles, disappearing into the optic disk, whilst its collaterals run mainly in the inner plexiform layer. A cell showing similar morphology has also been found in the ganglion cell layer of a cat retina. The second population of processes consists of very thick fibres (2.1 microns average diameter) apparently originating from the optic disk. The main branches run in the space between the optic fibre layer and the ganglion cell layer, with short, secondary processes crossing the ganglion cel layer orthogonally. Many higher-order processes originate from the second-order branches; these run almost horizontally in the inner plexiform layer. The ganglion cells generating axon collaterals may constitute an intraretinal firing synchronization system, or they may be a residual feature of retinal development. The centrifugal fibres may be related to the sensitivity control during retinal dark adaptation.

Animals↗

PubMed1991

An interplexiform cell in the goldfish retina: light-evoked response pattern and intracellular staining with horseradish peroxidase.

The light-evoked response pattern and morphology of one interplexiform cell were studied in the goldfish retina by intracellular recording and staining. The membrane potential of the cell spontaneously oscillated in the dark. In response to a brief light stimulus, the membrane potential initially gave a slow transient depolarization. During maintained light, the oscillations showed a tendency to be suppressed; the response of the cell to the offset of the stimulus was not so prominent. The perikaryon of the interplexiform cell was positioned at the proximal boundary of the inner nuclear layer. The cell had two broad layers of dendrites; one was diffuse in the inner plexiform layer, the other was more sparse in the outer plexiform layer. The morphological and electrophysiological characteristics of the cell are discussed in relation to dopaminergic interplexiform cells and the light-evoked release pattern of dopamine in the teleost retina.

Animals↗

PubMed1991

Computer aided tracing and encoding of axonal arborizations.

This paper reports a method of acquiring and codifying branching profiles of axonal arborizations. Using a microcomputer interfaced with a motor driven microscope scanning stage, an acquisition strategy was developed. This strategy allows large profiles (covering up to 1250 mm2) to be measured with an accuracy of a few microns. Each histological section is associated with a specific coordinate system. This system was found to locate the profiles with high precision and reliability in the x-y microscope stage. The overall tracing accuracy of the system is fully discussed.

Axons↗

PubMed1990

Variability of light-evoked response pattern and morphological characterization of amacrine cells in goldfish retina.

Amacrine cells of the goldfish retina were characterized electrophysiologically and subsequently labelled by intracellular injection of horseradish peroxidase. An attempt was made to broaden the electrophysiological classification of the cells. Light-evoked sustained amacrine cell responses were divided into two subtypes depending on colour opponency. Colour-coded responses (red/depolarizing and green/hyperpolarizing) were found to arise in amacrine cells possessing highly polarized dendritic fields; the dendrites were monostratified in the proximal half (sublamina b) of the inner plexiform layer. Non-colour-opponent sustained responses also arose in monostratified units, but the level of dendritic ramification was in sublamina a or b (hyperpolarizing or depolarizing units, respectively). Transient (ON-OFF) responses were associated mainly with bi- or multi-stratified or diffuse amacrine cells. Some variability was observed in the sizes of the dendritic fields in different sublaminae. There was a tendency for units with brisk components of responses to be narrowly stratified in the inner plexiform layer. Some units possessed "distant" dendrites. Several aspects of structure-function correlation in amacrine cells are discussed.

Animals↗

PubMed1989

Populations of retinal neurones marked with DAPI in lower vertebrates.

Retinae of teleosts, the marine sparid Boops boops and the fresh water cyprinid Carassius auratus, and amphibians, the anuran Rana pipiens and the urodele Ambystoma tigrinum, were stained in vitro with DAPI (4'6-diamidino 2-phenylindole). In all the preparations tested DAPI consistently stained nuclei in the ganglion cell layer, and three levels of nuclei could be observed from IPL (inner plexiform layer) to INL (inner nuclear layer) in the bogue, goldfish and frog retinae. In the goldfish retina a dense mosaic of stained horizontal cell nuclei was also observed. Both single and double cones were stained in fish; no photoreceptor staining could be found in amphibian retinae. Goldfish and frog retinae were incubated with 5'7'-DHT (dihydroxytryptamine) to compare the distribution of DAPI-stained cells with that of putative serotoninergic neurones. Fluorescent cells were found in the ganglion cell layer, and at two levels distally. In fixed retinae only a regular array of cells was found in the proximal INL, and interestingly the cell density equalled the density of serotoninergic amacrine cells. No other fluorescing cells could be detected. In the fixed frog retina two populations of fluorescent cells were found in the INL. For both species tested 5'7'-DHT and DAPI fluorescent populations did not overlap. The images of fluorescent cells were then processed, in order to improve image quality and assess if, in living tissue, cell types could be separated according to differences in intensity of fluorescence. It emerged that the size of fluorescent nuclei is inversely proportional to their optical density.

Amphibians↗

PubMed1986

Relation between light responses and dendritic branching in the salamander ganglion cells.

Ganglion cells in larval tiger salamander retina were differentiated into different types according to their light response and morphology. Sustained hyperpolarizing responses were recorded from ganglion cells branching in the sclerad half of the inner plexiform layer (IPL). Sustained depolarizing responses were elicited in cells with dendrites confined in the vitread portion of the IPL. Transient responses were associated with two types of morphological units sharing level of branching, in the middle of the IPL, but differing for soma location (inner plexiform or inner nuclear layer).

Animals↗

PubMed1984

GM1 micelles modify the transport properties of the ionophore gramicidin D in artificial planar bilayers.

We have analyzed the effects induced in different phospholipid planar bilayers by monosialoganglioside micelles containing the ionophore gramicidin D. The membrane conductance increases after the addition of GM1 micelles at various ionophore/ganglioside ratios. We believe this fact may be ascribed to gramicidin molecules that incorporate into the bilayer together with gangliosides. In the presence of micelles the mean lifetime and the amplitude of the gramicidin single channel did not present relevant modifications when dioleoylphosphatidylcholine or phosphatidylserine were used to form the bilayer. Calcium proved to trigger the interaction between phosphatidylethanolamine membranes and GM1 micelles containing gramicidin. In this case the ionic pore presents a longer lifetime and a lower amplitude with respect to pure gramicidin. We suggest that different properties developed by gramicidin may depend on structural organization of gangliosides when incorporated into the phospholipid bilayer.

Biophysical Phenomena↗

PubMed1984

Effect of gangliosides on phospholipid bilayers: a study with the lipophilic ions relaxation method.

The presence of monosialoganglioside GM1 in dioleoylphosphatidylcholine black lipid membranes modifies the transport properties of the hydrophobic ion tetraphenylborate and the kinetics of relaxation of this ion after the application of a voltage step. At zero applied voltage, the difference in the relaxation time constants between pure phospholipid and ganglioside-phospholipid mixed membranes is large. This difference may possibly rise from changes in the membranes fluidity since it has been found that the two types of membranes do not show appreciable difference in thickness. A uniform distribution of GM1 in the membrane seems to be more probable than the presence of lateral phase separation phenomena. The partition coefficient of tetraphenylborate between the bathing NaCl solution and the membrane appears to depend on the ionic strength, which controls the screening effect of the Na+ ions on the COO- charged groups of the sialic acid of the ganglioside polar heads. Effects of dipolar potentials on the partition coefficient can be excluded, being the absorption plane of tetraphenylborate probably located outside the dipolar layer of the membrane.

Biological Transport↗

PubMed1983

Capacitance--voltage relationship in phospholipid bilayers containing gangliosides.

Changes in the position of the minimum of the parabolic capacitance-voltage curve allow the measurement of the amount of ganglioside present in artificial bilayers made with phosphatidylcholine-ganglioside mixtures and asymmetrically shielded with Ca2+. The screening effect of the ionic solution must be considered. With ganglioside/phospholipid molar ratios of up to 15%, all glycolipids can be found at the membrane surfaces.

Gangliosides↗

PubMed1982

Properties of ionic transport through phospholipid-glycolipid artificial bilayers.

The ionic transport properties of dioleoylphosphatidylcholine (DOPC) membranes containing various sphingolipids were studied. Particular attention was paid to membranes formed from beta-D-glucosylceramide (GlcCer) and DOPC. They showed a marked increase in ionic permeability (up to a factor 30 with respect to pure DOPC membranes), slight cation selectivity and almost linear behaviour of the current-voltage characteristic. Bilayers containing GlcCer showed a typical conductance decrease upon increasing the temperature. We suggest the formation of clusters containing GlcCer molecules in a solid-crystalline phase. The conductance increase might be due to ionic pathways through disordered boundary regions. An increase in the mechanical breakdown potential was observed in all membranes which contain sphingolipids.

Electric Conductivity↗