The roles of intracellular calcium ([Ca²⁺]_i) and Ca²⁺ sensitization in lipopolysaccharide (LPS) induced vascular smooth muscle (VSM) hyporesponsiveness are incompletely understood. To investigate these roles, contraction responses to endothelin 1 (ET 1) and 80 mM KCl, relaxation responses to nifedipine, the expression levels of mRNAs of ET-1 and its receptors (ETA or ETB), the expression levels of protein kinase C (PKC) and phosphorylation of Rho kinase (ROK), CPI-17 and MYPT1, and changes in aortic VSM cells [Ca²⁺]_i were measured in LPS-treated aortic rings from male Wistar rats (250 300g). LPS (10 µg.ml^-1, 20 h) decreased contraction induced by ET 1 (0.3-100 nM) or 80 mM KCl. LPS induced hypocontractility was not observed in the absence of external calcium, but LPS treated aorta remained hypocontractile on subsequent stepwise restoration of extracellular Ca²⁺ (0.01-10 mM). Vascular relaxation to nifedipine, mRNA expression levels of ET-1, ETA or ETB, protein expression levels of PKC, and phosphorylation levels of ROK, CPI 17 and MYPT1 were not affected by LPS. In isolated aortic VSM cells, ET 1 caused a transient initial increase in [Ca²⁺]_i followed by a maintained tonic increase in [Ca²⁺]_i which was decreased by LPS-pretreatment and was dependent on external Ca²⁺. Subsequent restoration of extracellular Ca²⁺ increased [Ca²⁺]_i, but this increase was lower in the LPS treated group. This difference in response to extracellular Ca²⁺ addition was not affected by diltiazem, but was abolished by SKF 96365. Therefore, LPS induces hyporeactivity to ET 1 in rat aorta that depends on external Ca²⁺ influx through non VOCCs but not on ET 1 receptor expression or Ca²⁺ sensitization.