The blood brain barrier (BBB) is a higly specific, lipophilic barrier between the systemic blood circulation and the central nervous system. It is formed by the endothelium of brain capillaries characterized by a low rate of transcytosis, absence of fenestrations and the presence of tight junctions. Connexin hemichannels (HC) or hemi-gap junction channels are hexameric connexin channels that may function as a release pathway for Ca²⁺ mobilizing messengers contributing to paracrine and autocrine Ca²⁺ signal communication. Cytoplasmic calcium [Ca²⁺]_i is an important determinant of BBB permeability but little is known on the influence of [Ca²⁺]_i oscillations and [Ca²⁺]_i waves propagating between endothelial cells. Here, we investigated several conditions that trigger [Ca²⁺]_i oscillations/waves, determined the involvement of connexin HC and established their effect on BBB permeability. The work was performed on immortalized rat brain endothelial cells (RBE4) or primary bovine brain endothelial cells (BBEC). Exposure of these cells to solutions with lowered extracellular [Ca²⁺], a known trigger for HC opening, induced [Ca²⁺]_i waves and oscillations. The low extracellular [Ca²⁺] condition also induced an increase in BBB permeability in an in vitro model, which was inhibited by treatment with BAPTA-AM, a [Ca²⁺]_i chelator. Exposure of the cells to low concentrations of bradykinin (BK) induced [Ca²⁺]_i oscillations (not waves) that were inhibited by HC blockers and ATP degrading enzymes indicating a role for ATP possibly released via HC. Exogenous application of ATP also induced [Ca²⁺]_i oscillations but were not affected by HC blockers. Interestingly, BK increased BBB permeability whereas ATP did not have any effect. Our results thus show that BK and ATP induce endothelial [Ca²⁺]_i oscillations that are mediated by different mechanisms that furthermore act in a distinct manner on BBB permeability.