Effects of infrared (IR) radiation generated by a low-power Co2-laser on sensory neurons of chick embryos were investigated by organotypic culture method. Low-power IR radiation firstly results in marked neurite suppressing action, probably induced by activation of Na+,K+-ATPase signal-transducing function. A further increase in energy of radiation leads to stimulation of neurite growth. We suggest that this effect is triggered by activation of Na+,K+-ATPase pumping function. Involvement of Na+,K+-ATPase in the control of the transduction process was proved by results obtained after application of ouabain at very low concentrations. Physiological significance of low-power IR radiation and effects of ouabain at nanomolar level was investigated in behavioral experiments (formalin test). It is shown that inflammatory pain induced by injection of formalin is relieved both due to ouabain action and after IR irradiation.

Effects of infrared (IR) radiation generated by a low-power Co2-laser on the membrane of cultured dissociated nociceptive neurons of newborn rat spinal ganglia were investigated using the whole-cell patch-clamp method. Lowpower IR radiation diminished the voltage sensitivity of activation gating machinery of slow sodium channels (Nav1.8). Ouabain known to block both transducer and pumping functions of Na+,K+-ATPase eliminated IR irradiation effects. The molecular mechanism of interaction of Co2-laser radiation with sensory membrane was proposed. The primary event of this interaction is the process of energy absorption by ATP molecules. The transfer of vibrational energy from Na+,K+- ATPase-bound and vibrationally excited ATP molecules to Na+,K+-ATPase activates this enzyme and converts it into a signal transducer. This effect leads to a decrease in the voltage sensitivity of Nav1.8 channels. The effect of IR-radiation was elucidated by the combined application of a very sensitive patch-clamp method and an optical facility with a controlled Co2-laser. As a result, the mechanism of interaction of non-thermal low-power IR radiation with the nociceptive neuron membrane is suggested.

Several arginine-containing short peptides have been shown by the patch-clamp method to effectively modulate the Na_V1.8 channel activation gating system, which makes them promising candidates for the role of a novel analgesic medicinal substance. As demonstrated by the organotypic tissue culture method, all active and inactive peptides studied do not trigger the downstream signaling cascades controlling neurite outgrowth and should not be expected to evoke adverse side effects on the tissue level upon their medicinal administration. The conformational analysis of Ac-RAR-NH₂, Ac-RER-NH₂, Ac-RAAR-NH₂, Ac-REAR-NH₂, Ac-RERR-NH₂, Ac-REAAR-NH₂, Ac-PRERRA-NH₂, and Ac-PRARRA-NH₂ has made it possible to find the structural parameter, the value of which is correlated with the target physiological effect of arginine-containing short peptides. The distances between the positively charged guanidinium groups of the arginine side chains involved in intermolecular ligand–receptor ion–ion bonds between the attacking peptide molecules and the Na_V1.8 channel molecule should fall within a certain range, the lower threshold of which is estimated to be around 9 Å. The distance values have been calculated to be below 9 Å in the inactive peptide molecules, except for Ac-RER-NH₂, and in the range of 9–12 Å in the active peptide molecules.

Two short arginine-containing tripeptides, H-Arg-Arg-Arg-OH (TP1) and Ac-Arg-Arg-Arg-NH₂ (TP2), have been shown by the patch-clamp method to modulate the Na_V1.8 channels of DRG primary sensory neurons, which are responsible for the generation of nociceptive signals. Conformational analysis of the tripeptides indicates that the key role in the ligand-receptor binding of TP1 and TP2 to the Na_V1.8 channel is played by two positively charged guanidinium groups of the arginine side chains located at the characteristic distance of ~9 Å from each other. The tripeptide effect on the Na_V1.8 channel activation gating device has been retained when the N- and C-terminal groups of TP1 were structurally modified to TP2 to protect the attacking peptide from proteolytic cleavage by exopeptidases during its delivery to the molecular target, the Na_V1.8 channel. As demonstrated by the organotypic tissue culture method, the agents do not affect the DRG neurite growth, which makes it possible to expect the absence of adverse side effects at the tissue level upon administration of TP1 and TP2. The data obtained indicate that both tripeptides can have great therapeutic potential as novel analgesic medicinal substances.