Naumenko A. Smooth muscle excitation-inhibition and GABA-ergic regulation of rat hemodynamics under the action of nanostructured titanium dioxide

The thesis is devoted to the study of molecular and cellular mechanisms of action of nanostructured titanium dioxide on the excitation-inhibition of smooth muscles (SM) and the GABA-ergic regulation of rats’ circulatory function. The atomic emission spectrometry analysis of the rats visceral smooth muscles and organs intragastrally burdened with a titanium dioxide suspension (21 ± 5) nm showed that the greatest cumulation of Ti occurs in the stomach, caecum SM. This is accompanied by changes in mechanokinetic parameters, MU and AU indices of spontaneous contractions, the direction and magnitude of which are determined by the peculiarities of the mechanisms of their pacemaker activity and the duration of the burdening with nanomaterials. It was also established that under in vivo conditions, TiO2 (21 ± 5) nm modulates cholinergic excitation and excitation induced by K-induced membrane depolarization of smooth muscle cell membrane (SMC) of SM of the stomach and caecum, greatly enhancing the normalized maximum velocity of the energy independent component of high potassium and acetylcholine (AC) induced contracture. Under the same conditions, the action of TiO2 (21 ± 5) nm was accompanied by a significant violation of the kinetics of the formation of both the tonic and phase components of the myometrium SM contraction caused by oxytocin. Hlibenclamide and 5-hydroxydecanoate - the blockers of ATP-dependent conductivity of plasma membrane and mitochondrial membrane of myometrium SMC to K+ ions - (in vitro) did not eliminate the inhibitory effect caused by nanomaterial suspension on the mechanism of formation of the tonic component of SM, caused by this hormone. It was established that in vitro the cumulative effect of titanium dioxide suspensions (21 ± 5) nm, (4-8) nm and (1-3) nm changes the structure and kinetics of spontaneous contraction cycles of high potassium and acetylcholine contractures of the stomach smooth muscles, size and direction of which depends on the nanomaterial size. The molecular docking of TiO2 nanoparticle with M2 muscarinic receptor showed the absence of common binding sites with acetylcholine, however, it is possible that TiO2 forms the bonds with some amino acids of the binding site of M2 receptor allosteric modulator LY2119620, and it will be effect on the affinity of this receptor to orthosteric ligands blocking their entry into the orthosteric site. Concerning muscarinic M3 type cholinergic receptor, there may be competitive relationships between titanium dioxide and acetylcholine for the binding within the site boundaries. It was also determined that titanium dioxide (21 ± 5) nm eliminates the nicotine-transformed M2 receptor-dependent restriction of Ca2+e entrance in the SMC caecum during cholinergic excitation and suppresses nicotine-induced contraction of the caecum smooth muscle and stomach against the action of histamine. Our studies have shown that microinjections of baclofen - the GABAB receptor agonist - into the medullary cardiovascular nuclei of normotensive rats were accompanied by the development of hypo- and hypertensive reactions. In this work, the structure of the full-length GABAB receptor was reconstructed and it was shown that the stabilization of the baclofen-receptor complex occurs due to electrostatic and cation-π-electron interactions; the holding of such a complex during molecular dynamics is not less 100 ns. It was also established that microinjections of nanostructured TiO2 suspensions into the medullary nuclei of the medulla oblongata lead to changes in rats blood pressure, the magnitude and direction of which depended on the concentration and site of its introduction. Conducted molecular docking showed four potential binding sites of TiO2 to the extracellular part of the GABA1A subunit of the GABAB receptor, two of which coincide with the binding site of baclofen with this receptor by localization and amino acid composition.