¹Anadolu University, Institute of Graduate Studies, Faculty of Pharmacy, Department of Pharmacology, Eskişehir, Türkiye DOI : 10.29228/jrp.828 Mammals have approximately 80 genes that encode potassium (K+) channels. They have a wide range of physiological functions, such as modulation of action potential duration and relaxation of smooth muscles. Carvacrol, a compound found in various aromatic plants, has been used traditionally for treating asthma, menstrual spasms, and gastrointestinal disorders. However, its mechanism of action on smooth muscles remains insufficiently understood. This study investigates the role of potassium ion channels in the relaxing effects of carvacrol on isolated rat duodenum smooth muscles. Rats were euthanized and duodenal segments were prepared and placed in an isolated organ bath with Krebs’ solution. The segments were equilibrated for 1 h and then treated with chemicals to obtain concentrationresponse curves. The data were evaluated using one-way Analysis of Variance (ANOVA) and Tukey's Honest Significant Difference (Tukey’s HSD) test for multiple comparisons. Our findings demonstrate that carvacrol induces a dosedependent relaxation of these muscles. The relaxation effects were significantly reduced in the presence of specific potassium channel inhibitors, including paxilline, UCL1684, linopirdine, barium chloride, and 4-aminopyridine. They were completely blocked by the combination of barium chloride and tetraethylammonium. However, glibenclamide, ruthenium red, and nitroarginine did not alter the relaxing effects of carvacrol. In conclusion: carvacrol relaxes duodenum smooth muscles by opening barium chloride-sensitive Kir2.1 and Kir3.1, as well as tetraethylammoniumsensitive KCa1.1, KCa2.1, KCa2.2, KCa2.3, Kv1.2, Kv1.4, Kv1.5, Kv2.1, Kv2.2, Kv4.1, Kv4.2, Kv4.3, Kv7.1, Kv7.2, Kv7.3, Kv7.4, and Kv7.5 potassium channels. Keywords : Carvacrol; Ion channel; Transient receptor potential; Potassium; Duodenum; Smooth muscle