ADP-evoked Ca2+ transients in IB4-positive neurons. Examples of isolated neurons characterized by Fura-2 Ca2+ imaging and IB4-binding. Neurons were labeled with IB4 prior to use, photographed and then tested by Ca2+ imaging for responsiveness to 50 mM K+ to identify healthy neurons, then ADP (100 μM). Some of these neurons were also tested with α,β-me ATP, a selective agonist for P2X3-containing ion channels (100 μM, αβ-me ATP). Two representative traces are shown from a single field: Cell 1 responded to αβ-me ATP and ADP and bound IB4. Cell 2 did not respond to αβ-me ATP or ADP and did not bind IB4. Scale is shown as the change in relative fluorescence units (ΔF) versus time (sec).