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Biomedical subjects

E Ujec

Publications and source records attributed to E Ujec.

At least 19 recordsLinked to original sources
PubMed2004

Activation and modulation of ligand-gated ion channels.

Ligand-gated ionic channels are integral membrane proteins that enable rapid and selective ion fluxes across biological membranes. In excitable cells, their role is crucial for generation and propagation of electrical signals. This survey describes recent results from studies performed in the Department of Cellular Neurophysiology, Institute of Physiology ASCR, aimed at exploring the conformational dynamics of the acetylcholine, glutamate and vanilloid receptors during their activation, inactivation and desensitization. Distinct families of ion channels were selected to illustrate a rich complexity of the functional states and conformational transitions these proteins undergo. Particular attention is focused on structure-function studies and allosteric modulation of their activity. Comprehension of the fundamental principles of mechanisms involved in the operation of ligand-gated ion channels at the cellular and molecular level is an essential prerequisite for gaining an insight into the pathogenesis of many psychiatric and neurological disorders and for efficient development of novel specifically targeted drugs.

Allosteric Regulation↗
PubMed2002

Transepithelial potential in mesonephric nephrons of 7-day-old chick embryos in relation to the histochemically detected sodium pump.

In order to obtain basic information on the transport properties of differentiating embryonic nephrons, we examined the 7-day-old chick mesonephros by measuring the transtubular epithelial potential difference (TPD) and by histochemical detection of Na,K-ATPase activity. TPD as an indicator of the electrogenic transport was measured in individual segments of superficial nephrons in vivo. Their electric polarity was always lumen-negative. TPD was reduced by addition of 10 mM KCN applied to the mesonephric nephrons from the outside. In the proximal tubules, TPD was significantly lower (mean+/-SD: -1.0+/-0.5 mV) than in the distal and collecting tubules (-2.2+/-1.0 mV, p< or =0.05). Activity of the sodium pump was evaluated histochemically by detection of ouabain-sensitive potassium-dependent p-nitrophenyl phosphatase in cryostat sections of the mesonephros. The enzyme activity was demonstrated only in distal tubules and in the collecting ducts, but not in the proximal tubules. These findings have revealed significant differences between embryonic nephron segments: the distal tubule, in contrast to the proximal one, is supplied by the sodium pump and is able to generate higher TPD. Therefore, we consider that it is only the distal nephron, which possesses the ability of active transport.

4-Nitrophenylphosphatase↗
PubMed1993

A new technique for studying potential changes in nephrons of chick embryo kidneys in vivo.

To make the chick embryo accessible to electrophysiological measurements in its mesonephric kidney during the period between embryonic days (e.d.) 5 and 10, a special "chick-embryo-incubation bath" was constructed. It consists of an aerated chamber covering the egg and maintaining the gas exchange across the shell, and of a warmed reservoir of the incubation medium, into which the embryo is pulled out of the egg through a window in the shell. The two compartments are separated with a rubber membrane tightly fitting to the edges of the shell-window. The incubation medium contains a modified Krebs-Henseleit-Ringer solution and anesthetic Tricaine (Sigma). Access to the mesonephric nephrons is achieved by surgical excision of the body wall on the right side performed at e.d. 5. On average only about 35 percent of the operated embryos survive till the third day after surgery but during the next two days a mortality rate recedes to zero. The tolerance of short-term survival of embryos placed in the incubation bath was tested for up to 4 1/2 h. It was very good in embryos of age 5 to 7 e.d. as assessed by a steady heart rate and the presence of arterio-venous differences. A modified differential amplifier containing circuits for frequency compensation of the two channels was used for high-fidelity registration of voltage changes in the embryonic nephron with a single double-barrel microelectrode.

Animals↗
PubMed1989

Single K+ currents during differentiation of embryonic muscle cells in vitro.

After 3-7 days in culture, chicken myotubes possess five types of K+ channel: two high-conductance channels of 195 and 105 pS which are sensitive to tetraethylammonium (TEA), an ATP-sensitive channel of 64 pS and two low-conductance channels of 40 and 15 pS which are insensitive to TEA and ATP. The same population of channels is to be found in EGTA-treated muscle cells with blocked fusion and, with the exception of the ATP-sensitive channel, also in 1-day-old myoblasts. There are differences between myoblasts and myotubes in the percentage of incidence of individual channel types. High-conductance K+ channels are most frequently to be observed in myotubes, but they are rare in myoblasts and EGTA-treated cells where low-conductance K+ channels predominate.

Adenosine Triphosphate↗
PubMed1986

Evidence that excitatory amino acids not only activate the receptor channel complex but also lead to use-dependent block.

The effects of fast application of excitatory amino acids N-methyl-D-aspartate (NMDA), L-aspartate (ASP), L-glutamate (GLU), quisqualate (QU) and kainate (KAIN) were studied in neurons from the embryonic spinal cord of the chick in monolayer cultures by employing the 'patch clamp' technique in the 'whole cell' mode. It was found that NMDA, ASP, GLU and QU, but not KAIN, induced responses that exhibited several components. The early component decayed with a time constant of 2 s to a lower level of membrane current and discontinuation of the application was followed by an after-current which returned to the base-line with a time constant of about 7 s. It is suggested that NMDA, ASP, GLU and QU, but not KAIN, not only activate the receptor channel complex but also induce use-dependent block.

Amino Acids↗
PubMed1985

The postnatal functional development of muscle stretch receptors in the rat.

The response to a 5-sec stretch of the triceps muscle was studied in dorsal root filaments L5 of 72 infant rats (1-19 days old) under urethane anesthesia. More than 50% of all units in 1-day-old rats responded by repetitive firing until the end of the 5-sec stretch (slowly adapting or SA receptors), while the rest ceased to fire earlier (relatively rapidly adapting or 1/2 SA receptors), or gave an "on" response only. The number of units exhibiting an SA response increased with age and attained 80% in 5-day-old rats. By the 10th day of life, almost 90% of endings behaved as SA receptors. During development, the maximal discharge frequencies at the peak of stretch increased markedly, and their values in 18-day-old rats were comparable to those in adult rats. The phasic component of the response to stretch, although less well defined in the younger animals, was already present even in 1-day-old rats. Adaptation of the static response during maintained stretch was relatively steep in all the age groups studied. The results indicate that, in the rat, large numbers of muscle stretch receptors are capable of responding to sustained stretch as SA receptors, even at an age when their morphological and ultrastructural maturation is not yet fully accomplished.

Adaptation, Physiological↗
PubMed1985

Single non-inactivating K+ channels in the myotubes of the chick embryo in tissue culture.

Single-channel K+ currents were studied in the myotubes from the chick embryo grown in tissue culture for 4--9 days by employing the patch clamp technique. The "cell attached" configuration was used and the pipette was filled with a solution containing 3 mmol.l-1 K+. The channels exhibited a high conductance of approximately 90 pS and the probability of finding them open increased by an e-fold factor for 13 mV depolarization for low levels of activity. The channels did not inactivate during long-lasting depolarization. These channels have been suggested to contribute to delayed rectification.

Animals↗
PubMed1985

Sodium transport and electrical properties of the chick chorioallantoic membrane.

Transport and electrical properties of the chick chorioallantoic membrane (CAM) were studied in order to find the osmoregulatory organ which helps to compensate the renal filtration-reabsorption disbalance of chick embryos. It could be shown that CAM resembles Na+ transporting epithelia in that active Na+ absorption is responsible for the potential difference and short circuit current, which could be abolished by ouabain on the ectodermal and amiloride on the endodermal side. The transepithelial conductance rose with increasing sodium concentration in accordance with the Michaelis-Menten kinetics. The allantoic sac thus plays a role similar to the toad urinary bladder despite the low potential difference and resistance which indicate that CAM is a leaky epithelium. CAM is therefore not only a respiratory but also an osmoregulatory organ.

Allantoin↗
PubMed1983

The measurement of K+e concentration changes in human muscles during volitional contractions.

Changes of extracellular potassium concentration [( K+]e) were measured in human muscles during volitional isometric contractions using liquid ion-exchanger electrodes. In principle, an intramuscular injection needle containing a microelectrode with a side-pore was inserted into the brachioradialis muscle. After insertion of the needle, the glass ion-selective microelectrode (ISM) could be moved out of the protective trocar shield into the muscle tissue. The average values of [K+]e in human muscles during maximal effort rose from 4.5 mmol/l K+ to 9.5 mmol/l K+. These values correspond closely to those previously found in muscles of experimental animals.

Extracellular Space↗
PubMed1981

Projection of tooth pulp afferents to the brainstem and to the cortex in the cat.

The projection of tooth pulp afferents in the spinal trigeminal nucleus (N.V.sp.) and the effect of dorsolateral medullotomy on cortical potentials evoked by electrical stimulation of Adelta tooth pulp nerve fibres were studied in cats. It was confirmed that antidromic responses were recorded in the tooth pulp nerve to stimulation of the ipsilateral but not the contralateral N.V.sp.[11]. Dorsolateral medullotomy at the level of the obex did not alter the cortical potentials induced by single pulses applied to the tooth pulp. It is concluded that Adelta tooth pulp afferents project exclusively to the ipsilateral trigeminal nucleus and that the impulse transmission to the cortex persists after transection of the pars caudalis of the N.V.sp.

Afferent Pathways↗
PubMed1981

Slow potential changes in experimental neocortical propagated foci.

During and following interhemispheric stimulation (HS), characteristic negative slow potential changes (NSPCs) appeared which coincided with defined patterns of epileptic phasic field potentials (PFPs). Stimulus time-locked, high-amplitude, interhemispheric responses (IHRs), interictal and ictal patterns were accompanied by typical moderate NSPCs. In the wake of the latter, giant NSPCs occurred, concurrent with Van Harrevelds convulsions and/or either total or partial spreading, or local depressions. Partial depression of the PFPs and spreading of the moderate NSPCs were also present in the IHR stage. It is suggested that the moderate and giant NSPCs characterize two distinct types of experimental epileptogenesis which differ in the extent of alteration of the extracellular ion activities.

Action Potentials↗
PubMed1979

Low impedance coaxial K+ selective microelectrodes.

A procedure for preparing coaxial K+ selective microelectrodes with a low longitudinal resistance (Re) of the liquid ion exchanger selective barrel is described. The low resistance was attained by inserting another microelectrode filled with 0.5 mol . 1-1 KCl into the ion-exchanger column (Corning 477317). The lower longitudinal resistance decreases the noise level and consequently increases the resolving power five times. This modification makes it possible to measure small and rapid K+ concentration changes.

Electrophysiology↗