OPTM4102 Anatomy of Phototransduction & Visual Cycle PDF

OPTM4102 Anatomy of phototransduction Dr. Jason Charng [email protected] Acknowledgement of country The University of Western Australia acknowledges that its campus is situated on Noongar land, and that Noongar people remain the spirit...

OPTM4102 Anatomy of phototransduction Dr. Jason Charng [email protected] Acknowledgement of country The University of Western Australia acknowledges that its campus is situated on Noongar land, and that Noongar people remain the spiritual and cultural custodians of their land, and continue to practise their values, languages, beliefs and knowledge. Artist: Dr Richard Barry Walley OAM Objectives Phototransduction cascade Visual cycle  Photoreceptor diameter smaller in compare to the loves Found in : ↑ Outer retina, made up of cones and rods No rods at fovea - Periphery· --- rod dominated main function : Convert light energy into electrical energy https://pubmed.ncbi.nlm.nih.gov/21750765/ Webvision.med.utah.edu https://pubmed.ncbi.nlm.nih.gov/25892740/  Photoreceptor anatomy Inner segment all the proteins that is also responsible for Synthesizing required for photoreceptors. RAFA T# it EBTEAN Cilium is responsible for traffic in proteins manufacture Rod photoreceptor : - I for rod for come ↑H it https://pubmed.ncbi.nlm.nih.gov/21750765/ Webvision.med.utah.edu spherule vs. pedicle  Transduction of photoreceptor. (Conversion of photons to electrctrical energy). Dark current Rod photoreceptor 2 Dark current when in the dark O Nat travels to the ~ Maintains resting potential of rods inner segment via depolarized atG-40 mV, The flow of cation (+ ) maintains it -40MV concentration gradient. at depolarized state in dark. photoreceptors are in. Before been pumped out at the inner Maintained by Na+/K+ATPases in segment via the Nat/kt AtPases the inner segment > -. Constant release of the excitatory O Bring/pump Kt into inner of me This pump kt flow out segment neurotransmitter glutamate non-gated , energy requires inner segment via - kt channel. https://pubmed.ncbi.nlm.nih.gov/21750765/ - constant release Glutamate - of  READ THESE * Nat = Park current refers to the flow of ions particularly sodium cell when they ions photoreceptor : , , into the are not exposed to light. => Rod photoreceptors maintain a relatively depolarized state (-40MV) compare to other neurons in the dark. => This depolarization is due to the influi of Nations through CGMP-gated channels located in the outer rod photoreceptor segment of the. => The intracellular concentration of cyclic guanosine monophosphate (cGMP) is high these , keeping channels open. => Potassium ions flow out of the inner segment , which help maintain the overall membrane. potential Role of Sodium-potassium pump : actively transports Not & K into the cell to maintain the ionic balance & cell. potential -  Rod activation Photons activate the phototransduction cascade leads to ( Closure of the cGMP-Na+ =>↓ dark current channels creduces stop) , not kt C Because channels still (still are. open K+ channels still open have movement of K out of the photoreceptor. T Outward flow of kt Hyperpolarisation of : resulting photoreceptor membrane (-70 mV) negative => more Decrease in glutamate release wit stag of 3 pathways activate the next. https://link.springer.com/chapter/10.1007/978-981-287-846-5_8  Phototransduction cascade * 1 2 3 5 4 Activated PDE Convert cGMP to GMP. ↓ cGMP causes closure of CGMP-gated channel. https://webvision.med.utah.edu/  Phototransduction cascade Step 1: Light photon activates rhodopsin. Rhodopsin is converted to metarhodopsin II and made up 3 units B 2 by : , Step 2: Metarhodopsin II activates transducin - attach to GDP GDP dissociates from transducin GTP attaches to transducin. The alpha subunit (GTP attached) detaches from the other 2 subunits. Step 3: The alpha-subunit GTP complex binds to both ends of the phosphodiesterase (PDE) molecule, activating PDE Step 4: Activated PDE converts cGMP within the outer segment to GMP Step 5: Decrease in cGMP in within the outer segment Closure of cGMP dependent channels. => prevent the flow of Nat & Cat from [ some causing : Subsequent decrease in dark current. extracellular phase in outer segment.. ↑ dark current.  Phototransduction cascade - deactivation GTP must be converted back GC : guanylate cyclase ↓ restconsible for the synthesis of 1 2 to GDP