Characterization of [Ca2+
]i responses to ATP and UTP in cultured spinal neurons. A. Concentration dependency of [Ca2+]i increase elicited by ATP (◆) or UTP (▲) in primary cultured spinal neurons. B. Effect of P2 antagonists on ATP-evoked [Ca2+]i increase in spinal neurons. Fura-2-loaded spinal neurons were sequentially stimulated with 1 μM ATP, 1 μM ATP with 100 μM suramin, 100 μM RB-2 or 10 μM A-317491, and then 1 μM ATP in HBS at more than 30-min periods for washing between stimulation, fluorescence images were taken at 5 sec intervals. Neurons that the ATP-evoked [Ca2+]i increase was considerably reduced were taken as antagonized and expressed as % of ATP-responsive cells (54 for suramin, 117 for RB-2, and 118 for A-317491).