Astrocytes communicate with each other by the release of the ‘gliotransmitter’ ATP. It is hypothesized that intercellular communication between astrocytes may help to synchronise their activity. A primary function of astrocytes is the regulation of extracellular potassium ([K⁺]_o), by the process of potassium spatial buffering. In the absence of effective [K⁺]_o regulation, the build-up of K⁺ released during axonal activity results in a conduction block. Here, we have examined the effects of blocking gap junctions (GJ) and ATP-mediated communication between astrocytes on axonal excitability, in the isolated intact rat optic nerve. Rats of the Wistar strain, aged postnatal day (P)15-20 were killed humanely by cervical dislocation, in accordance with Home Office regulations. Optic nerves were isolated intact and removed to a brain slice chamber where they were continuously perfused with artificial cerebrospinal fluid (aCSF). The compound action potential (CAP) was measured using suction electrodes, during stimulation at 1 Hz, to serve as a baseline, and during increased stimulation at 20Hz or 35Hz for 120s. The effects of the following were examined, all at 100μM (added directly to aCSF): BaCl₂ to block glial Kir; carbenoxolone to block GJ; and the non-specific P2 receptor antagonist suramin, and the P2X7 receptor antagonist oxidized ATP (oATP), to block ATP-mediated intercellular communication. Results were tested for significance using one way-ANOVA with post-hoc Newman-Keuls test (significance was set at p<0.05 for all statistical analysis, n=4-6 for all observations). In aCSF, stimulation at 20Hz or 35 Hz for 120s resulted in a significant and activity-dependent decay in the CAP (Table 1). This decay was significantly greater following treatment with BaCl₂, oATP or suramin, but not carbenoxolone. In the case of suramin and oATP, the effects were greater at 35Hz than 20Hz. The results indicate that blocking Kir caused a significant decay in optic nerve conduction, and that blocking P2 and P2X7 receptors had an equivalent effect. This study supports a role for ATP-mediated astrocyte communication in [K⁺]_o regulation and maintaining axonal action potential conduction.