Synaptic transmission mediated by internal calcium stores in rod photoreceptors.
Retinal rod photoreceptors are depolarized in darkness to approximately -40 mV, a state in which they maintain sustained glutamate release despite low levels of calcium channel activation. Blocking voltage-gated calcium channels or ryanodine receptors (RyRs) at the rod presynaptic terminal suppressed synaptic communication to bipolar cells. Spontaneous synaptic events were also inhibited when either of these pathways was blocked. This indicates that both calcium influx and calcium release from internal stores are required for the normal release of transmitter of the rod. RyR-independent release can be evoked by depolarization of a rod to a supraphysiological potential (-20 mV) that activates a large fraction of voltage-gated channels. However, this calcium channel-mediated release depletes rapidly if RyRs are blocked, indicating that RyRs support prolonged glutamate release. Thus, the rod synapse couples a small transmembrane calcium influx with a RyR-dependent amplification mechanism to support continuous vesicle release.
Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York 14214, USA.
Anuradha
A
Suryanarayanan
Malcolm M
MM
Slaughter
D000557:Ambystoma; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D002121:Calcium Channel Blockers; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine