Effects of Electron Radiation on Serotonin Signaling and Reactivity of Rat Gastric Smooth Muscle

Ionizing radiation in radiotherapy can disrupt cellular functions based on radiation type, energy, and dose. However, investigations on the effects of accelerated electrons, particularly on serotonin mediation, are limited. This study aimed to investigate changes in serotonin signal transduction (targeting 5-HT_2A and 5-HT_2B receptors) in gastric smooth muscle (SM) samples isolated from rats irradiated with accelerated electrons (linear accelerator Siemens Primus S/N 3561) and their effects on serotonin-induced reactions. The radiation effects were examined in samples prepared five days after the procedure. The contractile activity of smooth muscle samples was measured using an isometric method. The expression of 5-HT_2A and 5-HT_2B receptors was determined by immunohistochemical assay. Increased contractile reactivity to exogenous serotonin (1.10^-8-1.10^-4 mol/L) was observed in irradiated samples compared to controls. The expression of 5-HT_2A and 5-HT_2B receptors was significantly increased in the irradiated tissue. By selecting appropriate time intervals between equimolar (1.10^-6 mol/L) sequential serotonin exposures, a process of desensitization associated with agonist-induced internalization was established in control samples, which was absent in irradiated samples. In conclusion, irradiation with accelerated electrons affects the agonist-induced receptor internalization of 5-HT_2A and 5-HT_2B receptors and increases their expression in rat gastric SM, which alters their contractile reactivity to exogenous serotonin.