Figure 1.

RyRs mediate glutamatergic synaptic input to bipolar cells. A, Light response of a rod-dominated OFF bipolar cell voltage clamped at −70 mV (dark trace) to a 2 s light stimulus. Ryanodine (100 μm; gray trace) application eliminated the light response, generated an outward current that aligns with the outward current produced by light, and suppressed synaptic noise. B, Light response of an ON bipolar cell held at −70 mV (dark trace) to a 2 s light stimulus. Ryanodine (100 μm; gray trace) suppressed the light response and produced an inward current in alignment with the decay phase of the light response, corresponding to constitutive opening of the metabotropic glutamate receptor cationic channels that are normally closed in the presence of glutamate in darkness. C, Glutamate at 100 μm was applied for 1 s (represented by bar above current trace) while recording an OFF bipolar cell clamped at −70 mV (dark trace). During treatment with 100 μm ryanodine, the puff of glutamate was reapplied (gray trace). Note that the glutamate current was unchanged in the presence of ryanodine, although synaptic noise was reduced. D, Cadmium (100 μm) was applied to the retina to block voltage-gated calcium channel-dependent synaptic transmission while recording from an OFF bipolar cell clamped at −70 mV (dark trace). Then, 10 mm caffeine was applied in the presence of cadmium, producing an EPSC in the OFF bipolar cell (gray trace).