Brain capillary pericytes have been suggested to play a role in the regulation of cerebral blood-flow under physiological and pathophysiological conditions. ATP has been shown to cause constriction of capillaries under ischemic conditions and suggested to be involved in the "no-reflow" phenomenon. In order to investigate the effects of extracellular ATP on pericyte cell contraction, we studied purinergic receptor activation of cultured bovine brain capillary pericytes. We measured [Ca2+]i-responses to purinergic agonists with the fluorescent indicators fura-2 and Cal-520 and estimated contraction of pericytes as relative change in cell area, using real-time confocal imaging. Addition of ATP caused an increase in cytosolic calcium and contraction of the brain capillary pericytes, both reversible and inhibited by a purinergic receptor antagonist PPADS. Furthermore, we demonstrated that ATP-induced contraction could be eliminated by intracellular calcium-chelation with BAPTA, indicating that the contraction was mediated via purinergic P2 -type receptor-mediated [Ca2+]i-signaling. ATP stimulation induced inositol triphosphate signaling, consistent with the notion of P2Y receptor activation. Receptor profiling studies demonstrated presence of P2Y1 and P2Y2 receptors, using ATP, UTP, ADP and the subtype specific agonists MRS2365 (P2Y1) and 2-thio-UTP (P2Y2)). Addition of specific P2X agonists only caused a [Ca2+]i increase at high concentrations, attributed to activation of inositol triphosphate signaling. Our results suggest that contraction of brain capillary pericytes in vitro by activation of P2Y type purinergic receptors is caused by intracellular calcium release. This adds more mechanistic understanding to the role of pericytes in vessel constriction, and points towards P2Y receptors as potential therapeutic targets.