Variability of activity concentrations and radial distributions of 137Cs and 90Sr in trunk wood of Scots pine and Silver birch.

This study analyzes the variability of 137Cs and 90Sr concentrations in wood and their radial distributions in the trunks of Scots pine and Silver birch trees in the small uniformly contaminated forest stands in the Chornobyl Exclusion Zone. Concentrations of both radionuclides follow a lognormal distribution with a large scatter of values measured in the trees within the stands (GSD ranges from 1.6 to 2.0). No correlation was found between the concentrations of the two radionuclides measured in individual trees, or between their concentrations and tree diameter. The average 137Cs and 90Sr Tag were 8.4 × 10-4 m2 kg-1 and 8.8 × 10-3 m2 kg-1 for pine, respectively, and 9.3 × 10-4 m2 kg-1 and 1.1 × 10-2 m2 kg-1 for birch, indicating a much higher availability of 90Sr for uptake by the studied species. For 137Cs, the Tag values are within the range recommended by the IAEA Handbook (IAEA, 2010), while the values for 90Sr exceed the recommended range for birch and are close to its upper value for pine. The highest concentrations of 137Cs in pine at the height of 1.3 m were measured in the youngest sapwood rings; they were lower in the rest of the sapwood and decreased further in the heartwood, but remained relatively high even in annual rings that were the heartwood at the time of deposition, suggesting sapwood-to-heartwood translocation of the radionuclide by diffusion and/or ray transport. In contrast, 90Sr concentrations increased through the sapwood from the trunk periphery in pine trees up to 80 years old and remained stable through the sapwood in older trees (except for higher concentrations in the young annual rings), but dropped to zero in physiologically inactive heartwood tissues. In most birch trees, regardless of age, 137Cs concentrations demonstrated an increasing trend from the trunk periphery towards the pith, while concentrations of 90Sr were relatively stable in the whole trunk except in the oldest annual rings, where they increased sharply, likely indicating active transport of the radionuclide to senescing tissues.

[Pretective action of peptide pro-gly-pro on electrophysiological characteristics of cultured hippocampal neurones during excitotoxic damage].

Electrophysiological characteristics of hippocampal neurones cultured with Pro-Gly-Pro peptide were studied using glutamate excitotoxisity model (excitotoxic damage was induced by 100 mkM glutamate application during 5 min). It was found that negative changes in neurones cultured with 10 mcM Pro-Gly-Pro were less prominent if compared with control ones. Culturing with the peptide significantly affected the following parameters: resting potential (-55 +/- 4 mV in control; -29 +/- 6 MV after glutamate application; -38 +/- 5 MV cultured after glutamate application), action potential amplitude (91 +/- 4; 65 +/- 5; 84 +/- 5 mV), duration (4,3 +/- 0,4; 9,5 +/- 1,6; 5,2 +/- 0,7 ms), depolarization (56 [38, 84]; 27 [21, 35]; 46 [28, 62] MV/Ms) and repolarization (-29 [-38, -27]; -20 [-21, -18]; -29 [-33, -22] M(V)/MS) rates. The data obtained suggest that PGP exhibit its neuroprotective properties on a level of basic electrophysiological characteristics, appropriate cellular mechanisms require further investigations.

[Changes in the kinetics of calcium signals in response to high frequency stimulation in the cultured hippocampal neurons].

Dynamic changes in the intracellular free Ca2+ concentration ([Ca2+]i) were studied in hippocampal cultured neurons using fluorescent Ca(2+)-indicator dye Indo-1 and somatic whole-cell recordings. During the tetanus stimulation Ca(2+)-transient increased their amplitude up to a steady-state level during repetitive stimulation. We identified two groups of neurons based on Ca-signal dynamics after the end of stimulation: the first group (n = 24) with the monoexponential decay of [Ca2+]i direct after the end of the tetanus; the second group (n = 32) with the monoexponential delayed [Ca2+]i decay after the end of the tetanus, the duration of delay varied from 1 to 27 s and depended on duration and frequency of stimulation. Peak amplitudes of Ca(2+)-transients were statistically different between the first (1820 +/- 195 nM, n = 24) and the second (2618 +/- 165 nM, n = 23) groups. A linear dependence between decay time constant and frequency of stimulation was found for the second group of neurons only. In all cases when the delayed decay was observed the decay time constant changed reliably after emergence of delayed decay; the average rise made up 41 +/- 8%. We suggest dynamic changes and essential rise in the intracellular free Ca2+ concentration arise from the presence of intracellular low-affinity buffer. This statement is to be further tested using pharmacological approach.

[Voltage-activated potassium channels of the inhibitory interneurons of the hippocampus in culture].

Potassium channels make up the largest family of voltage-activated channels and play a key role in maintenance of cell excitability and in transmission of information within the nervous system. The aim of this work was to find out the specific subtypes of voltage-activated potassium channels peculiar to GABAergic interneurons of rat hippocampal culture. It was shown that total depolarization-evoked outward potassium current in any interneuron studied had the activation threshold about -50 mV. The specific Kv1 channels' blocker a-DTX influenced neither amplitude nor kinetics of total current, thus we excluded the participation of these channels in its forming. The transient A-current made up 9.4+/-1.3% of the amplitude of total current and had low sensitivity to 4-AP that was an evidence of the presence of Kv4 channels in hippocampal interneurons. The slow inactivating component of integral potassium current was relatively small and had the time constant of inactivation 3 +/- 0.15 s that is typical for delayed rectifier potassium channels of Kv2 and Kv3 subfamilies. The main contribution (83 +/- 1.7 % of total amplitude) to the integral current belonged to the non-inactivating current. Prolonged depolarization of any interneuron tested to -20 mV evoked a steady non-inactivating outward current with amplitude 100-400 pA and activation threshold about -60 mV. Retigabine shifted its I-V plot to more negative values and increased the amplitude at -20 mV by 66+/-14%. These facts can be evidence of the participation of KCNQ channels subfamily in the forming of non-inactivating current. But selective blockers of KCNQ channels linopirdine and XE991 had very small influence on steady-state outward current that means the current appears owing to activity of linopirdine-insensitive forms of KCNQ channels or channels of a different, unknown family.

[Electrophysiological properties of inhibitory neurones in cultured dissociated hippocampal cells]. / Elektrofiziolohichni vlastyvosti hal'mivnykh neironiv u dysotsiiovanii kul'turi klityn hipokampa.

Electrophysiological properties of inhibitory (GABAergic) neurones were studied in dissociated hippocampal culture using simultaneous whole cell recordings from pairs of monosynaptically coupled neurons. Reliable identification of GABAergic neuron was performed by presence of monosynaptic inhibitory currents at postsynaptic cell in response to action potentials at stimulated cell. It was shown that GABAergic neurons in hippocampal culture are divided in two groups by their firing characteristics: first type generates action potentials at high frequency in response to injection of current (duration 0.5 s)--fast-spiking neurons (FS), cells from second type has no ability for high-frequency action potential generation--regular spiking neurons (RS). These two groups were distinguished by kinetic characteristics of action potentials, adaptation characteristics during continuous generation of action potentials and inhibitory effect making on postsynaptic cell. Application of potassium channel blocker 4-AP to somas of FS neurons in concentration, which selectively inhibits Kv3 potassium channels evoked reversible changes in kinetic of action potentials, frequency and adaptation characteristics during continuous generation of action potentials. It was concluded that there is hight level of expression of Kv3 potassium channels in the first group of neurons.