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.
Complete conformational analysis of 1 : 1 calcium(II) chelates with ouabagenin was performed ab initio. Analysis of the effect of complex formation on the steric and electronic structures revealed that ouabagenin molecule is capable of coordinating Ca 2+ ion in three different modes. The lack of rhamnose fragment in the ouabagenin molecule, in contrast to ouabain, sharply reduces its physiological activity related to its ability to bind at transducer Na + /K + -ATPase site.Cardiotonic steroids constitute a class of compounds capable of selectively binding to extracellular surface of Na + /K + -ATPase; the latter is an enzyme which utilizes the energy of ATP hydrolysis for active transport of Na + and K + ions through cell membranes [1][2][3][4]. This class of compounds includes both glycosides (such as ouabain and digoxin) and aglycones (ouabagenin, strophadogenin, adonitoxigenin). Clinical applications of cardiotonic steroids is based on their ability to exert a positive inotropic effect on myocard via partial inhibition of Na + /K + -ATPase in myocard cells [4]. The results of recent studies have shown that Na + /K + -ATPase can act as signal transducer which controls nociceptive information transmission in sensor neurons of warm-blooded animals [5], as well as cell growth and proliferation in various tissues [6][7][8][9][10][11][12][13][14].Using the organotypic tissue culture technique, it was shown that ouabain in nanomolar concentration range (which is comparable with the endogenous ouabain level) is capable of modulating transducer function of Na + /K + -ATPase in nervous and cardiac tissues [11][12][13]15]. Ligand-receptor interaction of ouabain molecule with some amino acid sequence of the enzyme is likely to involve formation of the ternary complex ouabain-Ca 2+ -Na + /K + -ATPase [15]. Nonempirical quantum-chemical calculations showed that ouabain molecule is theoretically capable of chelating Ca 2+ ion, and six possible conformations of the complexes thus formed were found [15]. In continuation of our studies on the ability of cardiotonic steroids to modulate transducer activity of Na + /K + -ATPase, we examined the effect of ouabagenin [1β,3β,5β,11α,-14β,19β-hexahydroxycard-20(22)-enolide] on the growth of neurites of sensor ganglia and cardiac tissue explants in 10-12-day chicken embryos using the organotypic tissue culture technique. Ouabagenin at
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