Ultrastructural characteristics of interstitial cell of Cajal-like cells of the muscular membrane of the gallbladder wall in an experimental study of mice under the influence of ursodeoxycholic acid. SI «Dnipropetrovsk Medical Academy of Ministry of Health of Ukraine», Dnipro, Ukraine. ABSTRACT. Background. The use of ursodeoxycholic acid drugs in the treatment of diseases of the hepatobiliary system is highly effective. Іnterstitial cell of Cajal-like cells are involved in the generation and propagation of spontaneous rhythms and, consequently, the excitability of the gallbladder. The purpose of the study was to determine the morphological changes of Іnterstitial cell of Cajal-like cells of muscle of the gallbladder wall of experimental mice under the action of ursodeoxycholic acid. Methods. The experimental study was performed on 30 mice of the BALB / c line. By the method of simple randomization, the experimental animals were divided into 2 groups: experimental (n = 17) -animals that received ursodeoxycholic acid at a dose of 100.0 mg / kg and control (n = 13) -intact (distilled water). The study was performed using a transmission electron microscope PEM-100-01 according to a standard scheme. Results. The muscular wall of the gallbladder of mice contains numerous interstitial cells in the developed endomysium, among which heteromorphic interstitial cell of Cajal-like cells (telocytes) were found in both study groups, containing from 2 to 8 processes, often with branches. The elongated bodies of these cells ranged in size from 8 to 30 μm. The nucleus showed signs of moderate activity, the cytoplasm contained a small number of general-purpose organelles, with the exception of numerous dense small mitoc-?ondria and developed agranular endoplasmic reticulum. Characteristic of interstitial cell of Cajal-like cells was the presence of numerous contacts of the processes with the membrane of neighboring leiomyocytes. A significant increase in the number of interstitial cell of Cajal-like cells in the muscular membrane of the bottom and body of the gallbladder was observed after the introduction of ursodeoxycholic acid. The ultrastructural features of their nuclear and cytoplasmic activity did not differ from those of the control group of animals. Conclusion. Thus, ultrastructural analysis of samples of the muscular wall of the gallbladder wall of mice revealed a significant increase in the number of interstitial cell of Cajal-like cells in the muscular membrane of the bottom and body of the gallbladder after the introduction of ursodeoxycholic acid.