Figure 4.

ipRGC Ca²⁺ responses are not attributable to Ca²⁺ release from intracellular stores. A, ipRGC light responses were abolished in Ca²⁺-free external solution. However, note the rise in [Ca²⁺]_i after exposure to Ca²⁺-free HBSS (with 2 mm BAPTA) and after the return to regular Ca²⁺-containing HBSS. B, Caffeine had no effect on [Ca²⁺]_i in ipRGCs maintained in Ca²⁺-free HBSS, indicating that Ca²⁺ stores had been emptied after exposure to zero external Ca²⁺. C, D, The Ca²⁺ stores depleting agent thapsigargin did not inhibit light-evoked [Ca²⁺]_i elevations (C), and ipRGC light responses persisted after emptying of stores by caffeine and thapsigargin (D). For all traces, hν indicates 20 s pulse of broad-spectrum light, 6.9 × 10¹³ photons/s/cm² at 480 nm.