Mechanokinetics of the spontaneous contractions of smooth muscles in the stomach and large intestine of rats under chronic effect of ТiО2 nanoparticles

Abstract

Background. Currently, nano-sized materials of titanium dioxide (TiО2) have wide industrial uses, particularly in the food industry and pharmacology. Therefore, the problem of TiО2 toxicity to living organisms in case of their chronic in vivo intake needs thorough investigation. As nanoparticles enter the internal environment of the body, they spread with the bloodstream to tissues and organs, where they partially accumulate. Thus studying the state of the pacemaker mechanisms of regulation of smooth muscle spontaneous contractions in the stomach and large intestine under chronic exposure to TiО2 nanoparticles is relevant and interesting. The purpose of this research work was to study the spontaneous contractile activity of the gastric and large intestine smooth muscles of rats under chronic (for 6 months) intake of an aqueous suspension of TiО2 nanoparticles. Materials and Methods. Wistar rats were used in the experiments. Rats of the experimental group were daily intragastrically administered an aqueous suspension of ТіО2 nanoparticles for six months at a dose of 0.1 mg/kg. The study of the mechanokinetics of the contraction-relaxation process of muscle preparations was carried out according to the method (Kosterin et al., 2021) with the calculation of the mechanokinetic parameters of the contraction-relaxation cycle: force (Fmax, FC and FR), time (τ0, τC and τR), impulse (Іmax, ІC and ІR) and velocity (VC and VR). Results. A comprehensive mechanokinetic analysis of spontaneous contractions of the antrum and caecum circular smooth muscles was carried out in control and under chronic in vivo exposure to ТіО2 nanocolloids (0.1 mg/kg/day) for 6 months. It was found that the chronic action of ТіО2 nanocolloids significantly inhibits the contractile activity of the antrum smooth muscles accompanied by a decrease in all mechanokinetic parameters of time, force, velocity and impulse. Under the same conditions, inhibition of the spontaneous contractions of the large intestine smooth muscles was observed. However, the time (τ0, τC and τR) and impulse (Іmax, ІC and ІR) parameters increased for these muscles against the background of the decrease in the force and velocity mechanokinetic parameters. Conclusions. Modulation of the mechanokinetic parameters of the spontaneous contractile activity of the stomach and large intestine smooth muscles of rats under chronic intragastric administration of ТіО2 nanocolloids suggests that the functioning of pacemakers changes significantly under these conditions. Since the parameters of the contraction and relaxation phases of both the stomach and the large intestine smooth muscles do not differ by the magnitude of the inhibitory effects, it can be assumed that the effects of ТіО2 are not specific for particular Са2+ transport systems involved in contractile responses.