PT  - JOURNAL ARTICLE
AU  - Shinya Sato
AU  - Beata Jastrzebska
AU  - Andreas Engel
AU  - Krzysztof Palczewski
AU  - Vladimir J. Kefalov
TI  - Apo-Opsin Exists in Equilibrium Between a Predominant Inactive and a Rare Highly Active State
AID  - 10.1523/JNEUROSCI.1980-18.2018
DP  - 2019 Jan 09
TA  - The Journal of Neuroscience
PG  - 212--223
VI  - 39
IP  - 2
4099  - http://www.jneurosci.org/content/39/2/212.short
4100  - http://www.jneurosci.org/content/39/2/212.full
SO  - J. Neurosci.2019 Jan 09; 39
AB  - Bleaching adaptation in rod photoreceptors is mediated by apo-opsin, which activates phototransduction with effective activity 105- to 106-fold lower than that of photoactivated rhodopsin (meta II). However, the mechanism that produces such low opsin activity is unknown. To address this question, we sought to record single opsin responses in mouse rods. We used mutant mice lacking efficient calcium feedback to boosts rod responses and generated a small fraction of opsin by photobleaching ∼1% of rhodopsin. The bleach produced a dramatic increase in the frequency of discrete photoresponse-like events. This activity persisted for hours, was quenched by 11-cis-retinal, and was blocked by uncoupling opsin from phototransduction, all indicating opsin as its source. Opsin-driven discrete activity was also observed in rods containing non-activatable rhodopsin, ruling out transactivation of rhodopsin by opsin. We conclude that bleaching adaptation is mediated by opsin that exists in equilibrium between a predominant inactive and a rare meta II-like state.SIGNIFICANCE STATEMENT Electrophysiological analysis is used to show that the G-protein-coupled receptor opsin exists in equilibrium between a predominant inactive and a rare highly active state that mediates bleaching adaptation in photoreceptors.