Objective: ERM proteins (Ezrin, Radixin and Moesin) are known to modulate the cell cytoskeleton through their binding to actin. They possess a FERM binding domain, which allows their interaction with EBP50. The purpose of this work was to study the interaction between moesin and EBP50 in intact arteries and their involvement in the regulation of vascular tone. Methods: Endothelium-denuded rat aorta and mesenteric artery were used. The interaction between moesin and EBP50 was tested by co-immunoprecipitation. The functional role of moesin and EBP50 was investigated in siRNA-transfected intact arteries. The efficiency of protein knock-down was assayed by RT-PCR and western-blot. Wire myographs were used to measure contraction. The Ca2+ sensitivity of the contraction was tested in ionomycin-permeabilized artery. Results: The interaction between moesin and EBP50 was promoted by 2 min stimulation of the artery with noradrenaline (1mM). Transfection of mesenteric arteries with siRNA against moesin selectively inhibited the expression of moesin protein by 41 ± 9 % (n=5) while anti-EBP50 siRNA selectively inhibited EBP50 protein expression by 61 ± 5 % (n= 5), compared to arteries transfected with scramble siRNA. EBP50 and moesin-depleted arteries similarly exhibited potentiated contractile response to noradrenaline, while the contraction evoked by KCl depolarization was unaffected. The contractile response measured in permeabilized arteries at pCa 6 was not different between arteries transfected with anti-moesin, anti-EBP50 or scramble siRNA. However, the concentration-response curve to noradrenaline at a fixed pCa of 6 was significantly and similarly shifted to the left in arteries transfected with anti-moesin siRNA or anti-EBP50 siRNA compared to arteries transfected with scramble siRNA. Conclusion: In intact artery, moesin - EBP50 interaction is activated by noradrenaline stimulation and modulates the calcium sensitivity of the contraction to the agonist.