Omega-conotoxin GVIA potently inhibits the currents mediated by P2X receptors in rat DRG neurons.

We examined effects of omega-conotoxin previously known as a selective blocker of N-type calcium channels, on the adenosine triphosphate (ATP)-induced currents in the rat dorsal root ganglion neurons. These neurons express at least two types of ionotropic purinoreceptors: P2X3 receptors that have very rapid desensitization kinetics and P2X2/X3 heterooligomeric receptor, which exhibits slow desensitization. We have found that omega-conotoxin GVIA potently inhibits the inward currents mediated by both receptor types. This effect was specific for the receptor subtypes: the IC(50) value for responses evoked by 10 microM ATP was 21.2 +/- 1.7 nM for the P2X3 receptor-mediated responses and 3.84 +/- 0.43 microM for slower responses mediated by P2X2/X3 heteropolymers. The efficacy of another type of omega-conotoxin, MVIIC, is much lower: at 10 microM the latter toxin inhibited the rapidly desensitizing response by 65% and the slowly desensitizing response by 18%. The effects of both toxins were reversible and independent on the membrane potential. Omega-Conotoxin GVIA shifted the dose dependence for the agonistic action of ATP on P2X3 receptors to higher concentrations without producing any effect on the kinetics of the response. It is suggested that omega-conotoxin allosterically modulates the receptor properties, rather than competes for the agonist binding site.

Steady magnetic fields effect on lipid peroxidation kinetics.

The effect of steady magnetic fields (ranging from 0 to 280 mT) has been investigated on the kinetics of non-enzymatic lipid peroxidation occurring in a model system consisting of liposomes obtained from 1, 2-dioleoylphosphatidylcholine by oxygen consumption. The process was found to be accelerated by weak steady magnetic fields. A computer simulation method was employed to detect the reactions that govern the process kinetics, to elucidate magneto-sensitive stages (initiation and reduction of iron(III), as well as lipid peroxide radical recombination) and to determine their rate constants at various external magnetic fields. The kinetics of peroxidation of lipid cell membranes have been modeled mathematically at oxygen and 'free' iron concentrations close to those in the cells and also at increased free iron concentrations at different external magnetic field values.

Heterogeneity of the functional expression of P2X3 and P2X2/3 receptors in the primary nociceptive neurons of rat.

The properties and functional expression of the purinergic receptors in small (nociceptive) neurons acutely isolated from the DRG of rat were studied using whole-cell patch-clamp recording. The responses of small DRG neurons to ATP exhibited diverse kinetics and could be subdivided into three types: rapid, slow and mixed kinetics responses. Their affinities to agonists allowed to identify the responsible receptors as P2X3 ("fast") and heteromeric P2X2/3 ("slow") subtypes. The expression of different responses dramatically varied both on the neuron-to-neuron and animal-to-animal basis. Out of 744 neurons tested 24% of cells demonstrated predominance of functional P2X2/3 receptors, 44% had mixed representation and in 32% of cells P2X3 receptors dominated. All the animals tested (110) could be subdivided into 3 groups: in 19% of animals the response of each cell to ATP was mediated by P2X2/3 receptors, both types of ATP-evoked currents were found in 58% of animals and only in 23% of the animals P2X3 receptors dominated. Our results argue with exclusive role of P2X3 receptors in purinergic signaling in primary nociceptive neurons.