Kulyk V. Opioidergic regulation of P2X3-receptors in the neurons of the spinal ganglia.

As part of this work, we have assessed the impact of endogenous opioid - leu-enkephalin P2X3 on the activity of receptors in neurons of the spinal ganglia. Also we outlined the role of biochemical pathways in the interaction of opioid receptors, which mediate analgesia with P2X3 receptors responsible for nociception. The thesis shows for the first time the double effect of endogenous opioid receptor agonist on currents mediated by P2X3 receptors in sensory neurons of spinal ganglia of rats. It is established that effect of P2X3-mediated currents in sensory neurons is supported by a G-protein coupled mechanisms. We have demonstrated that leu-enkephalin does not affect desensitization of P2X3-receptor and oppositely directed action of opioid on the receptors may be mediate by activation of pertussis toxin-sensitive G i/o and insensitive - Gq-protein. In particular it is shown that binding of leu-enkefalin to µ-opioid receptors leads to the simultaneous activation of both types of G-proteins, which would exert a dual effect on P2X3-receptors. However, in control conditions, we have recorded only inhibitory effect of opioids. The stimulating effect of endogenous opioids was masked and could be seen only in presence of pertussis toxin. Thus, using the method of "patch-clamp" we first show that endogenous opioid receptor agonist - leu-enkephalin causes two oppositely directed effects on P2X3-receptors. These effects are mediated by activation of at least two types of G-proteins and PLC.