Increase in [Ca2+
by caffeine in isolated DRG neurons. A, Brief puff of 10 mM caffeine for 1 or 2 s increased [Ca2+]i transients in DRG neurons (n = 9). B, Puff of 2 μM ryanodine increased [Ca2+]i transients (n = 9). C, Adding a high concentration of ryanodine (40 μM) to the extracellular solution blocked caffeine-induced increase in [Ca2+]i transients (n = 6). The cell color imaging (a-i) in the right side corresponded to the time points indicated (a-i) in the left side.