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Biomedical subjects

G Wójcik

Publications and source records attributed to G Wójcik.

At least 19 recordsLinked to original sources
PubMed2006

Studies of removal of platinum(IV) ion microquantities from the model solutions of aluminium, copper, iron, nickel and zinc chloride macroquantities on the anion exchanger Duolite S 37.

Platinum has been widely applied in catalytic industry and the recovery of noble metals from industrial wastes becomes an economic issue. The laboratory studies of platinum(IV) microquantities removal from 1M aluminium, copper, iron, nickel and zinc chloride solutions in 0.1M hydrochloric acid solutions on the anion exchanger Duolite S 37 of the functional secondary and tertiary amine groups were carried out. For this anion exchanger the fraction extracted values (%E, Pt(IV)) as well as the sorption isotherms were determined depending on the kind of aqueous phase and phase contact time. Moreover, the bed and weight distribution coefficients as well as working and total ion-exchange capacities were calculated from the platinum(IV) breakthrough curves. Kinetic parameters were determined.

Algorithms↗
PubMed2001

Variable-temperature crystal structure studies of m-nitroaniline.

The crystal structure of m-nitroaniline has been examined at several temperatures over the 90-350 K range. Thermal evolution of the lattice parameters reveals a weak anomaly at 110 K and an important one at 300 K. The thermal expansion coefficients have been calculated at several temperatures and the principal axes cross-sections of the tensor were drawn. The lattice contraction along the b axis direction has been observed. The rigid-body analysis including an attached rigid group has provided the values of the translation and libration tensors at temperatures studied. The results indicate that m-nitroaniline undergoes a glass transition around 130 K arising from freezing molecular librations and translations. From above 340 K the growing plasticity of the m-nitroaniline crystal results in the loss of X-ray diffraction reflections. This is probably a second-order phase transition. It is coupled with a considerable increase in the nitro group torsion amplitude, but the NH.O hydrogen bonds are preserved. Analysis of the temperature evolution of short intermolecular distances enabled us to consider the occurrence of reorienting aggregates of hydrogen-bonded molecules in the high-temperature plastic phase.

Journal Article↗
PubMed2001

Synthesis and spectroscopic characterization of protected N-phosphonomethylglycine dipeptides.

A series of terminally blocked dipeptides containing C-terminal N-phosphonomethylglycine (glyphosate, an extremely effective non-selective post-emergence herbicide) have been synthesized by a solution method. The presence of their two conformers, cis (syn) and trans (anti), was shown in solutions by NMR spectroscopy. Molecular structures of the peptides were also determined in the solid state by X-ray diffraction. The attempts for the selective and total removal of the groups protecting amino, carboxylic and phosphonate functions were in many cases unsuccessful due to the formation of cyclic structures and breakage of the phosphorus-to-carbon bond.

Glycine↗
PubMed2001

ATP-sensitive K+ transport in adrenal chromaffin granules.

In the present study the influx of 86Rb+, a K+ analogue, was studied in mitochondria, microsomes and chromaffin granules prepared from adrenal gland medulla. The most active electrogenic 86Rb+ transport was found in the membrane fraction identified as chromaffin granules by marker enzyme estimation. The transport was found to be sensitive to ATP, ATP gamma S, ADP and to the triazine dyes, but not to AMP and cAMP. The inhibition induced by ATP was observed in the absence of externally added Mg2+, suggesting that a free nucleotide, rather than the ATP-Mg complex, was required for inhibition. Furthermore, the 86Rb+ influx was found to be inhibited by Mg2+ alone, but not by Ca2+ and antidiabetic sulfonylureas. The 86Rb+ influx was not stimulated by potassium channel openers. In conclusion, our results indicate that an electrogenic, ATP-sensitive potassium transport system operates in the chromaffin granule membrane.

Adenosine Triphosphate↗
PubMed2001

The influence of the new benzodiazepine derivative BD-1158 on the behaviour of rabbits in spontaneous conditions.

BD-1158 is a new 1,4 benzodiazepine derivative. The purpose of the present experiments was to test the spontaneous behaviour (typical of a rabbit) after administration of BD-1158 and thus to define the activity and side effects of this substance under physiological conditions. The experiments were performed for 3 subsequent days in a group of 10 rabbits. On the first day spontaneous behaviour was tested. On the second day 1 ml of 1% starch solution was administered intraperitoneally. On the third day BD-1158 was administered intraperitoneally at a dose 10 mg/kg diluted in 1% starch solution up to 1 ml, 35-40 minutes before the beginning of the experiment. Six phases of behaviour were estimated. It was concluded that BD-1158 has a strong anxiolytic and sedative effect, decreases the state of animal's attention, water and food uptake.

Animals↗
PubMed1999

Modification of the mitochondrial sulfonylurea receptor by thiol reagents.

The purpose of this study was to investigate the effects exerted by thiol-modifying reagents on themitochondrial sulfonylurea receptor. The thiol-oxidizing agents (timerosal and 5, 5'-dithio-bis(2-nitrobenzoic acid)) were found to produce a large inhibition (70% to 80%) of specific binding of [(3)H]glibenclamide to the beef heart mitochondrial membrane. Similar effects were observed with membrane permeable (N-ethylmaleimide) and non-permeable (mersalyl) thiol modifying agents. Glibenclamide binding was also decreased by oxidizing agents (hydrogen peroxide) but not by reducing agents (reduced gluthatione, dithiothreitol and the 2,3-dihydroxy-1,4-dithiolbutane). The results suggest that intact thiol groups, facing the mitochondrial matrix, are essential for glibenclamide binding to the mitochondrial sulfonylurea receptor.

ATP-Binding Cassette Transporters↗
PubMed1997

The mitochondrial sulfonylurea receptor: identification and characterization.

Biochemical identification of mitochondrial sulfonylurea receptors has been carried out through binding studies performed with [3H]glibenclamide. The presence of a single class of low affinity binding sites for glibenclamide in the inner mitochondrial membrane has been found, with a KD of 360 +/- 48 nM and BMAX of 48 +/- 7 pmoles/mg in beef heart mitochondria. Glibenclamide binding was affected by other sulfonylureas (glipizide, glisoxepide) but not by potassium channel openers (diazoxide, pinacidil, RP66471). In both rat liver and beef heart mitochondria adenine nucleotides (ATP, ADP, AMP) and nucleotide analogs (triazine dyes) produced large inhibition (from 60 to 80%) of [3H]glibenclamide binding. Photoaffinity labeling of submitochondrial particles with [125I]-glibenclamide revealed a single specifically labeled polypeptide band of 28 kDa by SDS-PAGE that is postulated to be (or to form a part of) the mitochondrial sulfonylurea receptor.

ATP-Binding Cassette Transporters↗
PubMed1997

Pattern of ongoing discharge of single renal sympathetic neurons in the rabbit.

Ongoing discharge in single renal sympathetic neurons was first studied in vagotomized rabbits without baroreceptor information (60 min after section of the aortic nerves). Under urethane + chloralose anaesthesia interspike-interval histograms were compiled and discharge rates were measured in 79 neurons. The following parameters were analysed: (a) the shortest, (b) the preferred and (c) the longest interspike-intervals, (d) discharge rate, (e) spread of a histogram, (f) coefficient of symmetry, and (g) coefficient of variability. The type of distribution of histograms and 9 correlations between some parameters were also assessed. These parameters were considered to make up the pattern of the ongoing discharge. The shortest, preferred and longest interspike-intervals of the ongoing discharge were: 14.1 +/- 0.9, 30.4 +/- 3.5 and 1672 +/- 82 ms. The mean rate of discharge amounted to 1.78 +/- 0.08 spikes/s. Three out of 9 correlation coefficients between the above parameters were statistically significant. In a second part, the effect of section of the aortic nerves and of 4-aminopyridine (a drug known to enhance synaptic transmission) on the pattern of ongoing discharge were also studied. Ten minutes after section of the aortic nerves the rate of discharge significantly increased, the shortest interspike-interval diminished and coefficient of variability was not changed. The number of significant correlations rose from 3 to 9.4-Aminopyridine significantly increased the discharge rate, did not alter the shortest interspike-interval and increased the coefficient of variability. These data show that assessing several parameters of ongoing discharge making up its pattern may differentiate between the excitatory effects of section of the aortic nerves and administration of 4-aminopyridine and in this way help to elucidate the mechanisms of action of various factors affecting renal sympathetic discharge.

4-Aminopyridine↗
PubMed1997

Effects of K+ channel inhibitors on potassium transport in bovine adrenal chromaffin granules.

The Ca(2+)-independent K+ selective channel in the membrane of adrenal gland chromaffin granules has earlier been identified. In the present report we describe new properties of this potassium channel using 86Rb+, a K+ analogue, flux measurements. The studies are performed in membrane vesicles prepared from chromaffin granules. The electrogenic 86Rb+ transport is inhibited by quinacrine, barium, zinc and magnesium. The effects of other potassium channel blockers on 86Rb+ transport into chromaffin granules are also reported.

Adrenal Medulla↗
PubMed1996

Glibenclamide inhibits mitochondrial K+ and Na+ uniports induced by magnesium depletion.

Magnesium depletion induces K+ and Na+ uniports in rat liver mitochondria. The purpose of the present study was to investigate the effects exerted by the antidiabetic sulfonylurea, glibenclamide, a well known blocker of ATP-sensitive potassium channels, on mitochondrial K+ and Na+ uniports. The K+ and Na+ uniport activities were monitored indirectly, in energized mitochondria, by following K+ and Na+ influxes as measured by light scattering. The membrane potential of the mitochondria was determined using a TPP+ selective electrode. Equilibrium binding measurements of glibenclamide to the inner mitochondrial membrane was performed with [3H]glibenclamide. Mitochondrial K+ and Na+ uniports were found to be inhibited by glibenclamide in a concentration-dependent manner, with IC50 of 20 +/- 7 and 15 +/- 8 microM, respectively. On lowering of the pH value, the potency of glibenclamide to inhibit the uniports activity was increased. Binding studies revealed the presence of a single class of low affinity binding sites for glibenclamide in the inner mitochondrial membrane, with a Kd of 4 +/- 2 microM and a BMAX of 148 +/- 50 pmoles/mg of protein. The present study provides evidence that both mitochondrial K+ and Na+ uniport activities are sensitive to the antidiabetic sulfonylurea, glibenclamide.

Animals↗
PubMed1995

Potassium channel opener, RP 66471, induces membrane depolarization of rat liver mitochondria.

Effect of potassium channel openers on membrane potential of rat liver mitochondria was studied. It has been found that potassium channel opener RP 66471 induces depolarization of the mitochondrial membrane. Since neither the inhibition of mitochondrial respiration nor the uncoupling of mitochondria was observed concomitantly, the specific effect on the mitochondrial potential is postulated. Most likely the effect is caused by the increase of permeability of the inner mitochondrial membrane to potassium ions. Interestingly, however, it was found that no other potassium channel openers tested but RP 66471 was able to induce depolarization of mitochondrial membrane.

Animals↗
PubMed1993

Inhibition of renal nerve discharge by liminal stimulation of non-myelinated aortic afferents.

The pattern of inhibitory responses of sympathetic nerve discharge to liminal activation of aortic C-fibres was studied in rabbits. The animals were anaesthetized with urethane and chloralose and vagotomized. Sympathetic postganglionic discharge was recorded from single fibres of the renal nerve. Inhibitory responses were elicited by single shocks or short trains (2-5 shocks at 10 Hz) and assessed from peri-stimulus time histograms. Clear-cut inhibition of the sympathetic discharge was observed in 6 out of 10 fibres. It was evoked by one shock in 5 fibres and by two shocks in 1 fibre. The mean latency of the inhibitory response elicited by one shock was 318 +/- 18 ms and its duration amounted to 196 +/- 22 ms (mean +/- SE). The increase in the number of shocks prolonged the duration of the inhibitory response without markedly affecting their latency.

Animals↗
PubMed1991

Excitatory responses of the dorsal root discharge to stimulation of cutaneous and muscle afferents in the cat.

Excitatory responses of the dorsal root discharge (DRD) consisting in transient increase in its frequency have been studied in non-anaesthetized low spinal cats. They were evoked by stimulation of cutaneous nerves (superficial peroneal and posterior tibial) and muscle nerves (gastrocnemius-soleus and posterior biceps-semitendinosus), recorded from the central cut ends of single fibres of L7 dorsal roots. The excitatory responses were elicited by single volleys in low threshold cutaneous and group II muscle afferents. Group III afferents of gastrocnemius-soleus nerve were also effective. Increase in strength of stimulation of posterior biceps-semitendinosus nerve from 4T to 40T which activated group III muscle afferents significantly decreased the excitatory effects of the DRD. Incidence of excitatory responses of the DRD to volleys both in low and high threshold cutaneous afferents, was 100%. Frequency of occurrence of excitatory effects to volleys in group II muscle afferents ranged from 23% to 43% (for responses to posterior biceps-semitendinosus and gastrocnemius-soleus volleys, respectively). It was increased to 47% and 72% when excitatory effects were elicited by group III afferent volleys. These findings indicate that only some types of afferent fibres evoke excitatory responses of the DRD. Variable incidence of the excitatory responses to stimulation of cutaneous and muscle afferents suggests important difference in effectiveness of connections between both types of fibres and interneurones generating the DRD.

Action Potentials↗
PubMed1988

Long-lasting depolarization of the central terminals of cutaneous afferents in L7 segment evoked by volleys ascending from the sacral cord in the cat.

1. In 72% of non-anaesthetized spinal cats, single volleys ascending from the sacral cord evoke long-lasting primary afferent depolarization in L7 segment. It occurs in the central terminals of cutaneous but not in Ia muscle afferents. 2. Volleys descending to L7 segment evoke only short-lasting presynaptic depolarization. 3. It is concluded that presynaptic inhibition in L7 segment produced by ascending volleys is more effective than that evoked by descending volleys.

Afferent Pathways↗
PubMed1987

Interactions between inhibitions of sympathetic nerve discharge to successive stimulations of baroreceptor and cutaneous afferents.

Interactions between inhibitions of sympathetic nerve discharge (SND) to consecutive stimulations of A- and C-fibres in the aortic nerve and superficial peroneal (SP) nerve have been studied in rabbits anaesthetized with urethane and chloralose. SND was recorded from the renal nerve. At interval of 10 s following conditioning stimulation of SP nerve the test response of SND to activation of C-fibres (interaction SP-C) amounts to 83.7 +/- 7.5% (means +/- SE) of control. After applying both stimulations to the same SP nerve (interaction SP-SP) the test response of SND is significantly lower amounting to 56.3 +/- 3.9%. Comparable decrease of the effect of conditioning stimulation of one type of afferents on the test response to activation of other type of fibres was observed at interval of 10 s in two other interactions (SP-A and C-A). In seven interactions the conditioning stimulation of one type of fibres had no effect on the test response to stimulation of other type of fibres. This was found in one interaction at interval of 10 s (C-SP), in four interactions at interval of 20 s (SP-A, C-SP, SP-C and C-A) and in two interactions at interval of 40 s (SP-A and SP-C). Conditioning stimulations used in above interactions depressed the test responses to activation of the same type of fibres. It is suggested that the decrease or suppression of the effect of conditioning stimulation of one type of afferents on the test response of SND to activation of other type of fibres is related to disinhibition of this response.

Animals↗
PubMed1986

Conditioning of inhibition of sympathetic nerve discharge to stimulation of A- and C-fibres in the aortic nerve.

Stimulation of either A- or C-fibres in the aortic nerve inhibits sympathetic nerve discharge (SND) recorded from the renal nerve in rabbits anaesthetized with urethane. When the test inhibition of SND to stimulation of A-fibres is preceded by conditioning stimulation of the same afferents, the test response is depressed at shorter and facilitated at longer testing intervals. Facilitation of the inhibition of SND reaches 120% of control at a testing interval of 10 s. The recovery curve of inhibition of SND to activation of A-fibres has a time course of 17 s. Following conditioning activation only depression of the test inhibition of SND to stimulation of C-fibres is seen. It reaches 46% of control at an interval of 2 s and the recovery curve of inhibition of SND to stimulation of C-fibres has a time course of about 30 s. In other series of experiments the duration of the conditioning stimulation was varied while the testing intervals were fixed. At a testing interval of 2 s the reductions of the test responses are deeper and the durations of conditioning at which plateaus of depression are reached are longer with stimulation of C- than of A-fibres. Taken together with a longer recovery curve these findings suggest a more effective control of the test inhibition of SND by C-fibres. Opposite changes in the patterns of inhibition of SND to activation of either A- or C-fibres are explained by frequency-dependent post-tetanic effects of the conditioning stimulation.

Animals↗