To investigate the influence of titanium dioxide nanoparticles (TiO 2) on histamine-, nicotine-(acetylcholine-nicotine)-stimulated modulations of mechanical activity in smooth muscles of caecum and stomach of rats. Methods. Electronic scanning microscopy; zeta-potential estimation; the isometric tension recordings; pharmacological and kinetic analysis. Results. Relaxation of smooth muscles stripes (SMS) of caecum stimulated by 10-5 mol/l nicotine on the background of histamine contraction was not affected by TiO 2 (10-3 mg/ml); under the same conditions TiO 2 reinforced the histamine-induced contractions. The cumulative increase in TiO 2 concentration in the 10-6-10-4 mg/ml range was accompanied by inhibition of SMS contractions stimulated by histamine (10-5 mol/l) and nicotine (10-7 mol/l). Similar results were obtained on stomach SMS. The phase component of acetylcholine contraction modulated by nicotine was bound to be unaffected by TiO 2 whereas the tonic component was inhibited. Conclusions. The suspension of TiO 2 nanoparticles in conditions of cumulative effect modulates the mechanisms of neurotransmitter release from neurons of intramural ple xuses of circular smooth muscle of the gastrointestinal tract which are activated by histamine and nicotine (10-7 mol/l).

Electron scanning microscopy was used to obtain the image and identify the size of TiO 2 nanoparticles. Using the tenzometric method in the isometric mode, it was estab lished that chronic effect of TiO 2 on stomach smooth muscles led to redistribution of the amplitudes of spontaneous contractions in terms of their frequencies. An increase in frequency of their contractions, decrease in the duration of contraction-relaxation cycle, the disturbance of the asymmetry of the duration of contraction-relaxation development, a reduction in Montevideo index of contractions and Alexandria index of contractions were demonstrated. It was also shown the existance of the divergence in numerical va lues of frequency amplitude complexes, TiO 2 -modified spontaneous contractive activi ty of smooth muscles of stomach and caecum. In the conditions of long-term chronic influ ence (100 days), TiO 2 removes the regulatory mechanisms of depressing a release of inhibition neuromediators from neurons of the intramural nervous interlacement, medi ated by GABA А and GABA С receptors, in smooth musc les of stomach and caecum.