Effects of nitric oxide and hypoxia on low-and high-voltage activated calcium currents in murine DRG neurons

The effects of a nitric oxide (NO)-containing aqueous solution (authentic NO) and hypoxia on low-and high-voltage activated calcium currents (I _Ca,lva andI _Ca,hva , respectively; in the latter transient and sustained portions were differentiated) were studied in enzymatically dispersed medium-sized neuronal somata from the murine dorsal root ganglia (DRG). Authentic NO (10 μM) was found to decrease the mean peak amplitude ofI _Ca,lva , from 3.5±0.3 to 1.2±0.2 nA (n=11,p<0.001), as well as the amplitudes of transient and sustainedI _Ca,hva components from 4.5±0.1 to 2.7±0.2 nA and form 2.8±0.2 to 1.7±0.2 nA (n=11;P<0.001), respectively. This NO-induced suppression was reversible and was removed by 1-min-long washout. At the same time, medium-sized DRG neurons demonstrated relatively low sensitivity to hypoxia (P_O2=20–25 mm Hg): decreases of both types ofI _Ca under hypoxic condition were not statistically significant (n=11;p>0.05). The data strongly suggest that NO is capable of reversibly suppressing both types of calcium channels in murine DRG neurons and of modulating in this way their excitability. It seems likely that this ability is based on a direct effect of NO on the corresponding channels and not on NO participation in the induction of hypoxic effects. Yet, a hypothesis that NO is a messenger of hypoxic damage to neural cells still should be suggested.     

An unexpected effect of capsaicin on spontaneous GABA-ergic IPSCS in hippocampal cell cultures

Vanilloid receptors 1 (VRs1) expressed in a subpopulation of sensory neurons and responsible for processing of chemical and thermal noxious stimuli were also shown to be expressed in several cerebral structures and to be involved in the regulation of glutamatergic synaptic transmission. In this study, we started to investigate the possibility that VRs1 are also involved in the regulation of GABA-ergic synaptic transmission. For this purpose, the effect of a VR1 agonist, capsaicin, on spontaneous GABA-ergic inhibitory postsynaptic currents (IPSCs) was studied in hippocampal cell cultures using a patch-clamp technique. It was found that capsaicin (10 μM) decreased both the frequency and amplitude of spontaneous IPSCs. This finding suggests the involvement of VRs1 in the regulation of neuronal firing in some GABA-ergic interneurons and in the modulation of the efficacy of GABA-ergic synaptic transmission. However, considering the direction of the effect (a decrease in the IPSC frequency) and lack of its desensitization, the involvement of other receptor(s) also cannot currently be ruled out. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 364–367, July–August, 2006.     

An Exposure to the Oxidized DNA Enhances Both Instability of Genome and Survival in Cancer Cells

Background

Cell free DNA (cfDNA) circulates throughout the bloodstream of both healthy people and patients with various diseases and acts upon the cells. Response to cfDNA depends on concentrations and levels of the damage within cfDNA. Oxidized extracellular DNA acts as a stress signal and elicits an adaptive response.

Principal Findings

Here we show that oxidized extracellular DNA stimulates the survival of MCF-7 tumor cells. Importantly, in cells exposed to oxidized DNA, the suppression of cell death is accompanied by an increase in the markers of genome instability. Short-term exposure to oxidized DNA results in both single- and double strand DNA breaks. Longer treatments evoke a compensatory response that leads to a decrease in the levels of chromatin fragmentations across cell populations. Exposure to oxidized DNA leads to a decrease in the activity of NRF2 and an increase in the activity of NF-kB and STAT3. A model that describes the role of oxidized DNA released from apoptotic cells in tumor biology is proposed.

Conclusions/Significance

Survival of cells with an unstable genome may substantially augment progression of malignancy. Further studies of the effects of extracellular DNA on malignant and normal cells are warranted.     

4-(4-R-phenylamino)-5-methoxy-1,2-benzoquinones are new selective inhibitors of carbon tetrachloride-initiated free radical reactions in liver.

The action of several 1,2-benzoquinone derivatives on free radical processes initiated by carbon tetrachloride was studied. Among them a substance that effectively inhibited lipid peroxidation without substantial influence on covalent binding of radical products of metabolic cleavage of carbon tetrachloride as well a substance that equally inhibited both processes were found. It was shown that 1,2-benzoquinones can be useful tool for investigation of free radical mechanisms of carbon tetrachloride-initiated liver cell damage in vivo.     

Homeostatic plasticity of GABA-ergic synaptic transmission in rat hippocampal cell cultures

It has been shown recently that prolonged blockade of neuronal firing activates several homeostatic mechanisms in neocortical networks, including alteration of glutamatergic and GABA-ergic synaptic transmission, and postsynaptic changes are involved in both cases. We studied whether such treatment also affects GABA-ergic synaptic transmission in hippocampal cell cultures. Using whole-cell voltage-clamp recording and local extracellular stimulation, we investigated evoked inhibitory postsynaptic currents (IPSC) in cultured rat hippocampal neurons grown with the sodium channel blocker tetrodotoxin (TTX) and under control conditions. We found that chronic TTX treatment significantly decreased the amplitude of evoked IPSC. This decrease was accompanied by an increase in the coefficient of variation of the above parameter, which is suggestive of a presynaptic mechanism. In contrast, no changes in the IPSC reversal potential or paired-pulse depression were observed in TTX-treated cultures. We conclude that alteration of GABA-ergic synaptic transmission contributes to the homeostatic plasticity in hippocampal neuronal networks, and this change is at least in part due to a presynaptic mechanism.Neirofiziologiya/Neurophysiology, Vol. 36, Nos. 5/6, pp. 432–437, September–December, 2004.This revised version was published online in April 2005 with a corrected cover date and copyright year.     

Calcium Signaling in <Emphasis Type="Italic">Carassius</Emphasis> Cerebellar Neurons: Role of the Mitochondria

We studied the involvement of the mitochondria playing the role of a calcium store in the control of calcium exchange in cerebellar neurons of a fish species tolerant to hypoxia, crucian (Carassius gibelio). In our experiments we used an ionophore, CCCP, that blocked accumulation of calcium by the above organelles. The intracellular concentration of free Ca²⁺ ([Ca²⁺] _і ) was measured using a calcium-sensitive dye, Fura-2AM, and the microfluorescent technique. We found that cerebellar neurons of Carassius gibelio possess a well-expressed system clearing the cytoplasm from excessive Ca²⁺, and the mitochondria are actively involved in this process. Under conditions of suppression of the process of accumulation of calcium by the mitochondria under the action of CCCP, the amplitude of calcium transients increased by about 50%. In addition, the decay phase of depolarization-induced intracellular calcium transients was slowed down considerably. Therefore, our experiments are indicative of the significant role of the mitochondria in the control of calcium dynamics in cerebellar neurons of Carassius gibelio in the course of functional activity of these cells.