Background and Purpose Coordinated endothelial control of cardiovascular function is proposed to occur by endothelial cell communication via gap junctions and connexins. To study intercellular communication, the pharmacological agents carbenoxolone (CBX) and 18β glycyrrhetinic acid (18βGA) are used widely as connexin inhibitors and gap junction blockers. Experimental Approach We investigated the effects of CBX and 18βGA on IP₃-evoked intercellular Ca²⁺ waves in the endothelium of intact mesenteric resistance arteries. Key Results Acetylcholine (ACh)-evoked IP₃-mediated Ca²⁺ release and propagated waves were inhibited by CBX (100µM) and 18βGA (40µM). Unexpectedly, the Ca²⁺ signals were inhibited uniformly in all cells, suggesting that CBX and 18βGA reduced Ca²⁺ release. Localised photolysis of caged IP₃ (cIP₃) was used to provide precise spatiotemporal control of site of cell activation. Local cIP₃ photolysis generated reproducible Ca²⁺ increases and Ca²⁺ waves that propagated across cells distant to the photolysis site. CBX and 18βGA each blocked Ca²⁺ waves in a time dependent manner by inhibiting the initiating IP₃-evoked Ca²⁺ release event rather than block of gap junctions. This effect was reversed on drug washout, and was unaffected by small or intermediate K⁺-channel blockers. Furthermore, CBX and 18βGA each rapidly and reversibly collapsed the mitochondrial membrane potential. Conclusion and Implications CBX and 18βGA inhibit IP₃-mediated Ca²⁺ release and depolarise the mitochondrial membrane potential. These results suggest that CBX and 18βGA block cell-cell communication by acting at sites that are unrelated to gap junctions.