Biomedical subjects

C Zona

Publications and source records attributed to C Zona.

34 records · Page 2Linked to original sources

PubMed1993

Arachidonic acid augments potassium currents in rat neocortical neurones.

We analysed the effects induced by arachidonic acid on voltage-dependent outward currents generated by rat neocortical neurones in culture in the presence of Na+ and Ca2+ channel blockers. These currents, recorded with whole-cell voltage-clamping techniques, were presumably carried by K+ and were characterized by an early transient and a late persistent component. Extracellular application of arachidonic acid (50 microM) enhanced both components of the voltage-dependent K+ response by 15-29% (n > 20 cells). These effects were reversible and not observed when a low dose (50 microM) of indomethacin was present in the bath (n = 7 cells). We conclude that one or more of the arachidonic acid metabolites of the cyclooxygenase pathway might be involved in the modulation of outward currents in neocortical cells in culture.

Animals↗

PubMed1991

Modulation of voltage-activated channels by calcitonin gene-related peptide in cultured rat neurones.

1. Whole-cell currents were recorded from cultures of dissociated neocortical neurones of the rat. Rat alpha-calcitonin gene-related peptide (CGRP; 1 nM-1 microM) caused significant dose-dependent decreases in the voltage-activated transient (A-current) and delayed rectifier K+ currents. Forskolin (10 nM-20 microM) mimicked this effect. Peak K+ currents were gradually decreased after loading neurones with cyclic AMP (100 microM) through patch pipettes. CGRP was ineffective in neurones loaded with cyclic AMP. 2. CGRP (0.5-2 microM) increased cytosolic cyclic AMP concentration and this effect was mimicked by forskolin (5-40 microM). 3. CGRP (0.1-1 microM) reduced high-threshold Ca2+ currents; as did forskolin (5-20 microM) and cyclic AMP loaded into the neurones. In contrast, low-threshold Ca2+ currents were not affected by any of these agents. 4. Voltage-activated Na+ currents were significantly reduced by both CGRP (0.1-1 microM) and forskolin (5-20 microM). A similar effect was observed when cells were loaded with cyclic AMP. 5. We conclude that, in neocortical neurones, CGRP attenuates voltage-activated currents by stimulating the intracellular cyclic AMP signalling system.

Animals↗

PubMed1990

Interleukin-2 suppresses established long-term potentiation and inhibits its induction in the rat hippocampus.

The effects of recombinant interleukin-2 (rIL-2) on the potentiation of the synaptic transmission were studied in rat hippocampal slices by using extracellular field potential recordings. The application of rIL-2 inhibited the induction of both short-term (STP) and long-term potentiation (LTP) in a dose-dependent manner. In addition, rIL-2 (1000 U/ml) reduced both post-tetanic potentiation (PTP) and LTP maintenance phase. The possible involvement of rIL-2 action on the synaptic potentiation with the enzymatic activity of protein kinase systems is discussed.

Animals↗

PubMed1990

Glycosylation is required for maintenance of functional voltage-activated channels in growing neocortical neurons of the rat.

Voltage-activated currents were studied in whole-cell patch-clamped rat neocortical neurons growing in culture and treated with tunicamycin (TU), an inhibitor of protein N-glycosylation. The size of the Na+ current decreased progressively in the presence of TU (1-2 microM). This decrease was faster in growing 5-14 day-old neurons (to ca. 40% of control after 24 hours of treatment) than in fully grown 20-40-day-old neurons (to ca. 40% of control after 68 hours of treatment). The fast transient K+ current (A-current) was abolished, and the delayed rectifier K+ current was markedly reduced by a 24 hour treatment with TU (1-2 microM) in growing neurons. In contrast, in fully grown neurons these currents were unaffected by the same TU treatment. The size of the Ca2+ current was significantly reduced following a 24 hour treatment with TU (1-2 microM) in neurons at early stages of differentiation, but remained stable in 20-40-day-old neurons. It is concluded that protein glycosylation, presumably of the channel proteins themselves, is important for the functional expression of voltage-activated channels in embryonic cortical neurons during the early stages of cell growth in culture; the channels become less dependent on glycosylation in mature neurons.

Aging↗

PubMed1990

Low magnesium epileptogenesis in the rat hippocampal slice: electrophysiological and pharmacological features.

Extra- and intracellular recording techniques were used to study the epileptiform activity generated by rat hippocampal slices perfused with Mg2(+)-free artificial cerebrospinal fluid (ACSF). This procedure induced in both CA1 and CA3 subfields the appearance of synchronous, spontaneously occurring epileptiform discharges which consisted of extracellularly recorded 100-800 ms long, positive shifts with superimposed negative going population spikes. Simultaneous, extracellular recordings from CA1 and CA3 subfields revealed that the epileptiform discharges in CA3 preceded those occurring in CA1 by 5-25 ms. Surgical separation of the two areas led to the disappearance of spontaneous events in the CA1 but not in the CA3 subfield. In this type of experiment CA1 pyramidal cells still generated epileptiform discharges following orthodromic stimuli. The intracellular counterpart of both spontaneous and stimulus-induced epileptiform discharges in CA1 and CA3 pyramidal cells was a large amplitude depolarization with high frequency discharge of action potentials which closely resembled the paroxysmal depolarizing shift recorded in the experimental epileptogenic focus. A hyperpolarizing potential triggered by alvear stimuli was recorded in CA1 cells perfused with Mg2(+)-free ACSF. This hyperpolarization was blocked by bicuculline methiodide (BMI) indicating that it represented a GABAergic inhibitory postsynaptic potential (IPSP). BMI also caused a prolongation of both spontaneous and stimulus-induced Mg(+)-free epileptiform discharges. Perfusion of the slices with the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphono-valerate (APV) reduced and eventually abolished the Mg(+)-free epileptiform discharges. These effects were more pronounced in the CA1 than in the CA3 subfield. APV also reduced the amplitude and the duration of the alveus-induced IPSP. These data demonstrate that Mg(+)-free epileptiform activity is present in the hippocampal slice at a time when inhibitory GABAergic potentials are operant as well as that in the CA1 subfield this type of epileptiform activity is dependent upon NMDA-activated conductances. Our experiments also indicate that NMDA receptors might be involved in the neuronal circuit responsible for the hyperpolarizing IPSP generated by CA1 pyramidal neurons.

2-Amino-5-phosphonovalerate↗

PubMed1990

Effects induced by the antiepileptic drug valproic acid upon the ionic currents recorded in rat neocortical neurons in cell culture.

Rat neocortical neurons in culture were subjected to the whole cell mode of voltage clamping under experimental conditions designed to study Na+, Ca2+ and K+ currents in isolation. Following pharmacological blockade of most of the Ca2+ and K+ channels, depolarizing commands which brought the membrane potential from -80 to +10 mV elicited an inward current. This current was sensitive to tetrodotoxin (TTX) and was therefore caused by the opening of voltage-dependent channels permeable to Na+. Extracellular application of the antiepileptic drug valproic acid (VPA, 0.2-2mM) reduced in a dose-related, reversible way this Na+ current. VPA also evoked an increase of the voltage-dependent inward current recorded in the presence of TTX and thus presumably carried by Ca2+; this effect was seen in the presence of doses of VPA larger than 0.5 mM and was not reversible. Two types of outward K+ currents evoked by depolarizing steps in the presence of Na+ and Ca2+ channels blockers were not affected by VPA (up to 5 mM). Our data indicate that doses of VPA that are within the range present when it is used as an anticonvulsant, can influence inward currents generated by rat neocortical cells in culture. The reduction of the Na+, inward current is in line with findings obtained in mouse neurons by using standard intracellular recording techniques. This effect might represent an important mechanism of action for VPA in neocortex.

Animals↗

PubMed1990

Potassium currents in rat cortical neurons in culture are enhanced by the antiepileptic drug carbamazepine.

We report that carbamazepine (Tegretol), a drug that is useful for the treatment of complex partial seizures, enhances outward, voltage-dependent K+ currents generated by rat neocortical cells in culture and recorded with patch-clamping techniques. This effect is seen in the presence of therapeutic concentrations of carbamazepine (10-20 microM). Furthermore, at these doses carbamazepine does not influence voltage-dependent inward Na+ and Ca2+ currents recorded in these cells. The action exerted by carbamazepine on K+ currents is a novel finding and might represent an important mechanism for controlling neocortical excitability and thus the generation of epileptiform activity.

4-Aminopyridine↗

PubMed1989

Calcium-activated potassium channels recorded from rat neocortical neurons in cell culture.

Rat neocortical neurons in cell culture were studied with the patch-clamp technique in order to determine the properties of a large-conductance K+ channel in excised inside-out patches. In the presence of a physiological ionic gradient for K+ across the patch membrane ([K+]i = 120 mM; [K+]o = 3 mM), outward channel activity was detected when the patches were brought to membrane potential values less negative than -30 mV. Depolarization of the membrane increased the magnitude of the current. The I-V relationship displayed rectification at negative membrane potentials. When the I-V curve was differentiated the slope conductance calculated at 0 mV membrane potential was 120 pS. The single-channel permeability was 5.2 x 10(-13) cm/s and the current flow through the open K+ channel could be modeled using the constant-field electrodiffusion theory. K+ channel opening was not observed following removal of Ca2+ from the intracellular surface of the membrane. Our experiments indicate that, as in other cell types, rat neocortical neurons in culture exhibit a large-conductance K+ channel which is activated by Ca2+ acting on the cytoplasmic surface.

Animals↗

PubMed1989

Calcium currents in cultured rat cortical neurons.

Rat neocortical neurons grown in dissociated cell culture for 4-12 weeks were studied with whole-cell patch-clamp techniques in order to characterize the calcium currents present in these cells. When voltage-dependent Na and K currents were inhibited, depolarizations from negative holding potentials induced inward currents which had 3 components: a low threshold activated, small, relatively persistent component, which was completely inactivated at holding potentials more positive then -60 mV; a higher threshold, relatively persistent component (which was not inactivated at VH = -50 mV); and a higher threshold, larger, transient component. All 3 components were reduced by removal of Ca, and blocked by Cd and Ni at appropriate concentrations. The components were differentially affected by low concentrations of Ni (500 microM), nifedipine (500 microM) and Ba (1.8 mM). Only the first two components were present in very young neurons.

Animals↗

PubMed1988

Delayed and fast transient potassium currents in rat neocortical neurons in cell culture.

Cultured rat neocortical neurons were subjected to the whole-cell mode of voltage clamping to study outward K+ currents. Tetrodotoxin and Cd2+ were applied extracellularly to block Na+ and Ca2+ currents. Depolarizing voltage commands from a holding potential of -90 mV evoked an outward current which peaked early and decayed over 20-50 ms to attain a steady level. At holding potentials more positive than -50 mV, the fast, transient component of the outward current was largely inactivated while the late, steady one remained present. The two components of the outward current displayed different pharmacological sensitivities: the fast, transient one was blocked by 4-aminopyridine, while the late, persistent one was reduced by tetraethylammonium. These currents were present in neocortical cells as early as the third day in culture. Our experiments indicate that as in sympathetic, hippocampal and spinal cord neurons, neocortical cells possess both a fast, transient, and a delayed K+ current. These currents might play an important role in controlling neocortical excitability.

4-Aminopyridine↗

PubMed1986

Effect of different parameters on the binding of two anti-inflammatory drugs to human serum albumin.

The binding to human serum albumin of two anti-inflammatory drugs, indomethacin and indoprofen, has been studied by chromatographic and spectroscopic techniques. The results shown indicate that the binding of both drugs--but more notably of indoprofen--is very sensitive to variations of the environmental conditions. The binding is also dependent upon limited modifications in the tertiary structure of the protein. The evidences shown tend to indicate that these two phenomena are related, and that the binding is permitted under conditions of a relatively open structure of the protein molecule.

Chromatography, Gel↗

PubMed1984

[Determination of cardiac output by thoracic electric impedance: comparison with thermodilution].

When an alternating current of high frequency is applied to the thorax, the first derivative of the impedance (dZ/dt) is affected by the cardiac cycle, resulting in a characteristic wave form. The maximum negative of this wave occurring during systole together with the length of ejection time (VET), the blood resistivity, the basal impedance (ZO) and the distance between the inner detecting electrodes (L) makes it possible to calculate stroke volume (SV) and related parameters, as cardiac output (CO) and cardiac index (Cl) by a formula developed by Kubicek. Thoracic electrical impedance has been proposed as a non invasive technique to evaluate cardiac emodinamics. In the present study we have evaluated thoracic electrical impedance by comparing it with thermodilution, simultaneously performed in 21 catheterized patients. Reproducibility was assessed by comparing Cl measured several times in the same patient during ten minutes of rest in the supine position: coefficient of variation, expressed as CV = SD/m X 100 was 8,5 +/- 4,2% and 9,4 +/- 3,2% (p = NS) for thermodilution and thoracic electrical impedance respectively. Cl values obtained by both methods correlated well, with little scatter either baseline (r = 0,784, n = 40, p less than 0,001), either after an handgrip manoeuvre (r = 0,629, n = 15, p less than 0,05). This degree of correlation is similar to that observed comparing invasive techniques (Fick, thermodilution, dye dilution) either among them, or with noninvasive methods (echocardiography, gated equilibrium blood pool scintigraphy and ultrasonic Doppler).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1983

Partial purification and characterization of an escherichia coli toxic factor that induces morphological cell alterations.

A factor produced by several strains of Escherichia coli isolated from enteritis-affected children has been shown to produce both a necrotizing effect on rabbit skin and striking morphological alterations on CHO, Vero, and HeLa cells. The same strains were found to have hemolytic activity on sheep erythrocytes. The toxic, cell-altering factor was demonstrated to be different from both heat-labile and heat-stable enterotoxins and from Vero toxin. The main effect induced by the isolated factor on cultured cells was the formation of large multinucleated cells. The partial purification achieved suggests that the same factor (most likely a protein with a molecular weight of 70,000 to 80,000) is responsible for toxic and cell-altering activities, whereas a different molecular species is responsible for hemolytic activity.

Animals↗

PubMedDate not supplied

Digital processing of the current noise evoked by kainate in cerebellar granule cells.

Current induced in cultured cerebellar granule cells by the bath application of kainate (500 microM) was measured using the conventional patch-clamp technique. Two different kinds of responses were observed after the agonist perfusion. Some cells exhibited small inward whole-cell currents: 116 +/- 40 pA (7 cells) at a clamp potential of -60 mV; in other cells, the agonist induced significantly larger currents: 420 +/- 35 pA (6 cells) at a clamp potential of -60 mV. The current flowing in the agonist-activated ionic channels was indirectly estimated by processing the fluctuations of whole-cell current by means of an original parametric method. Mean conductance of the underlying channels was then determined from the single-channel current estimated at different clamp potentials. In the cells exhibiting small inward currents, the mean conductance was equal to 0.5 +/- 0.2 pS (7 cells), whereas in the cells with large inward currents it was 3 +/- 0.4 pS (6 cells). This result gives a coherent explanation of the different kinds of responses observed at macroscopic level in the whole-cell current and confirms that kainate-activated channels can exhibit different levels of conductance.

Animals↗

PubMedDate not supplied

Hydrolysis of leucine enkephalin and its association to the K562(S) erythroleukaemic cell line.

Hydrolysis of Leu-enkephalin and association to cells of the radioactive label carried by this peptide have been studied on the K562(S) erythroleukaemic cell subline. Data obtained indicate that in the presence of these cells Leu-enkephalin is rapidly hydrolyzed and that the peptide's radioactive label is partially associated to the cells. Both phenomena are characterized by distinctly diphasic kinetics, and are oppositely modified by cells' stimulated erythroid differentiation. In the presence of proteolysis inhibitors, hydrolysis of Leu-enkephalin and association to cells of its radioactive label are reduced. These data, indicating that enkephalin hydrolysis is a prerequisite for the association of the radiolabel to cells, are consistent with those obtained with other cell lines of different origins and with human mononucleate cells. The modifications induced by differentiation of cells on hydrolysis, association and membrane conductance can be interpreted as an indication of extensive modifications of the membrane structures responsible for the mechanisms controlling those phenomena.

Amino Acid Sequence↗

PubMedDate not supplied

Induction of epileptiform activity by temperature elevation in hippocampal slices from young rats: an in vitro model for febrile seizures?

Extracellular field potential recordings were performed in the CA1 subfield of hippocampal slices obtained from Wistar rats aged 2-38 days. When the brain tissue was maintained at 35 degrees-36 degrees C (values obtained in the tissue chamber well), single-shock orthodromic stimuli elicited a response in the stratum pyramidale that consisted of a single population spike. In contrast, when the temperature in the well was increased to levels greater than 38.2 degrees C for periods of 5-15 min, the same type of stimuli elicited an epileptiform response characterized by a 250- to 600-ms-long, positive-going field potential with superimposed, multiple, negative-going population spikes. This potential resembled the epileptiform response recorded in the hippocampal slice in the presence of convulsants such as penicillin or bicuculline. Once the temperature was restored to control values (i.e., 35 degrees-36 degrees C) after induction of epileptiform activity, the abnormal response could be observed for less than or equal to 2 h. In some experiments (approximately one third of the successful trials), spontaneous epileptiform discharges appeared during and persisted after the increase in temperature. The ability of the hyperthermic period to induce epileptiform changes was age dependent: Epileptiform activity outlasting the period of temperature elevation was not observed in slices obtained from rats aged less than 4 days or greater than 28 days. Our data show that epileptiform activity can be induced by a transient increase in temperature and that the age of the animals from which slices are obtained plays an important role in the appearance of this phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗