photoreceptor inner segment membrane
Definition
Target type: cellularcomponent
The membrane surrounding the inner segment of a vertebrate photoreceptor. The photoreceptor inner segment contains mitochondria, ribosomes and membranes where opsin molecules are assembled and passed to be part of the outer segment discs. [GOC:dph]
The photoreceptor inner segment membrane is a highly specialized cellular compartment that plays a crucial role in phototransduction, the process by which light is converted into electrical signals in the retina. This membrane is characterized by a complex architecture, enriched with a variety of proteins and lipids, and organized into distinct domains that facilitate specific functions.
One notable feature of the inner segment membrane is the presence of numerous invaginations, known as **ciliary membrane folds**. These folds increase the surface area of the membrane, allowing for efficient uptake of nutrients and oxygen from the surrounding environment. This is crucial for the high metabolic demands of photoreceptor cells, which are constantly engaged in phototransduction and signal processing.
The inner segment membrane also contains a specialized region known as the **synaptic terminal**, where photoreceptor cells form connections with other neurons in the retina. This terminal is enriched in synaptic proteins, including **SNARE proteins**, which play a critical role in vesicle fusion and neurotransmitter release.
In addition to these structural features, the inner segment membrane is also characterized by its unique lipid composition. This membrane is enriched in **phospholipids**, particularly **phosphatidylcholine** and **phosphatidylethanolamine**, which contribute to its fluidity and stability. It also contains a high concentration of **cholesterol**, which helps to maintain membrane integrity and regulate protein function.
Several proteins are specifically localized to the inner segment membrane and are critical for its proper function. These include:
* **Rhodopsin**: A light-sensitive protein responsible for capturing light and initiating the phototransduction cascade.
* **Transducin**: A G protein that acts as a signal transducer in the phototransduction pathway.
* **Phosphodiesterase**: An enzyme that breaks down cyclic GMP, a molecule involved in regulating light sensitivity.
* **Sodium-potassium pump**: A transmembrane protein responsible for maintaining ion gradients across the membrane, which is essential for generating electrical signals.
* **Calcium channels**: Ion channels that regulate calcium influx into the cell, playing a role in synaptic transmission and photoreceptor function.
The complex architecture and composition of the inner segment membrane are crucial for the efficient and precise functioning of photoreceptors. Disturbances in the structure or composition of this membrane can lead to various retinal disorders, highlighting its importance for maintaining normal vision.'
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Proteins (3)
| Protein | Definition | Taxonomy |
|---|---|---|
| Rhodopsin | A rhodopsin that is encoded in the genome of cow. [OMA:P02699, PRO:DNx] | Bos taurus (cattle) |
| Sodium/potassium-transporting ATPase subunit alpha-3 | A sodium/potassium-transporting ATPase subunit alpha-3 that is encoded in the genome of human. [PRO:DNx, UniProtKB:P13637] | Homo sapiens (human) |
| Sodium/potassium-transporting ATPase subunit alpha-1 | A sodium/potassium-transporting ATPase subunit alpha-1 that is encoded in the genome of human. [PRO:DNx, UniProtKB:P05023] | Homo sapiens (human) |
Compounds (16)
| Compound | Definition | Classes | Roles |
|---|---|---|---|
| lansoprazole | Lansoprazole: A 2,2,2-trifluoroethoxypyridyl derivative of timoprazole that is used in the therapy of STOMACH ULCERS and ZOLLINGER-ELLISON SYNDROME. The drug inhibits H(+)-K(+)-EXCHANGING ATPASE which is found in GASTRIC PARIETAL CELLS. Lansoprazole is a racemic mixture of (R)- and (S)-isomers. | benzimidazoles; pyridines; sulfoxide | anti-ulcer drug; EC 3.6.3.10 (H(+)/K(+)-exchanging ATPase) inhibitor |
| omeprazole | 5-methoxy-2-{[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]sulfinyl}-1H-benzimidazole : A member of the class of benzimidazoles that is 1H-benzimidazole which is substituted by a [4-methoxy-3,5-dimethylpyridin-2-yl)methyl]sulfinyl group at position 2 and a methoxy group at position 5. omeprazole : A racemate comprising equimolar amounts of (R)- and (S)-omeprazole. Omeprazole: A 4-methoxy-3,5-dimethylpyridyl, 5-methoxybenzimidazole derivative of timoprazole that is used in the therapy of STOMACH ULCERS and ZOLLINGER-ELLISON SYNDROME. The drug inhibits an H(+)-K(+)-EXCHANGING ATPASE which is found in GASTRIC PARIETAL CELLS. | aromatic ether; benzimidazoles; pyridines; sulfoxide | |
| pantoprazole | pantoprazole : A member of the class of benzimidazoles that is 1H-benzimidazole substituted by a difluoromethoxy group at position 5 and a [(3,4-dimethoxypyridin-2-yl)methyl]sulfinyl group at position 2. Pantoprazole: 2-pyridinylmethylsulfinylbenzimidazole proton pump inhibitor that is used in the treatment of GASTROESOPHAGEAL REFLUX and PEPTIC ULCER. | aromatic ether; benzimidazoles; organofluorine compound; pyridines; sulfoxide | anti-ulcer drug; EC 3.6.3.10 (H(+)/K(+)-exchanging ATPase) inhibitor; environmental contaminant; xenobiotic |
| digoxigenin | digoxigenin : A hydroxy steroid that consists of 5beta-cardanolide having a double bond at the 20(22)-position as well as hydroxy groups at the 3beta-, 12beta- and 14beta-positions. It has been isolated from the plant species of the genus Digitalis. Digoxigenin: 3 beta,12 beta,14-Trihydroxy-5 beta-card-20(22)-enolide. A cardenolide which is the aglycon of digoxin. Can be obtained by hydrolysis of digoxin or from Digitalis orientalis L. and Digitalis lanata Ehrh. | 12beta-hydroxy steroid; 14beta-hydroxy steroid; 3beta-hydroxy steroid; 3beta-sterol | hapten; plant metabolite |
| madecassic acid | monocarboxylic acid; pentacyclic triterpenoid; tetrol | antioxidant; plant metabolite | |
| digoxigenin-bis(digitoxoside) | cardenolide glycoside | ||
| rostafuroxin | rostafuroxin: structure in first source | ||
| nsc 88915 | 4-pregnen-21-ol-3,20-dione-21-(4-bromobenzenesufonate): a tyrosyl-DNA phosphodiesterase inhibitor; structure in first source | ||
| ouabain | cardiac glycoside : Steroid lactones containing sugar residues that act on the contractile force of the cardiac muscles. ouabain : A steroid hormone that is a multi-hydroxylated alpha-L-rhamnosyl cardenoloide. It binds to and inhibits the plasma membrane Na(+)/K(+)-ATPase (sodium pump). It has been isolated naturally from Strophanthus gratus. Ouabain: A cardioactive glycoside consisting of rhamnose and ouabagenin, obtained from the seeds of Strophanthus gratus and other plants of the Apocynaceae; used like DIGITALIS. It is commonly used in cell biological studies as an inhibitor of the NA(+)-K(+)-EXCHANGING ATPASE. | 11alpha-hydroxy steroid; 14beta-hydroxy steroid; 5beta-hydroxy steroid; alpha-L-rhamnoside; cardenolide glycoside; steroid hormone | anti-arrhythmia drug; cardiotonic drug; EC 2.3.3.1 [citrate (Si)-synthase] inhibitor; EC 3.1.3.41 (4-nitrophenylphosphatase) inhibitor; EC 3.6.3.10 (H(+)/K(+)-exchanging ATPase) inhibitor; EC 3.6.3.9 (Na(+)/K(+)-transporting ATPase) inhibitor; ion transport inhibitor; plant metabolite |
| digitoxin | digitoxin : A cardenolide glycoside in which the 3beta-hydroxy group of digitoxigenin carries a 2,6-dideoxy-beta-D-ribo-hexopyranosyl-(1->4)-2,6-dideoxy-beta-D-ribo-hexopyranosyl-(1->4)-2,6-dideoxy-beta-D-ribo-hexopyranosyl trisaccharide chain. Digitoxin: A cardiac glycoside sometimes used in place of DIGOXIN. It has a longer half-life than digoxin; toxic effects, which are similar to those of digoxin, are longer lasting. (From Martindale, The Extra Pharmacopoeia, 30th ed, p665) | cardenolide glycoside | EC 3.6.3.9 (Na(+)/K(+)-transporting ATPase) inhibitor |
| digoxin | digoxin : A cardenolide glycoside that is digitoxin beta-hydroxylated at C-12. A cardiac glycoside extracted from the foxglove plant, Digitalis lanata, it is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation, but the margin between toxic and therapeutic doses is small. Digoxin: A cardiotonic glycoside obtained mainly from Digitalis lanata; it consists of three sugars and the aglycone DIGOXIGENIN. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in ATRIAL FIBRILLATION and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. (From Martindale, The Extra Pharmacopoeia, 30th ed, p666) | cardenolide glycoside; steroid saponin | anti-arrhythmia drug; cardiotonic drug; EC 3.6.3.9 (Na(+)/K(+)-transporting ATPase) inhibitor; epitope |
| digitoxigenin | digitoxigenin : A 5beta-cardenolide that is 5beta-cardanolide with hydroxy substituents at the 3beta- and 14beta-positions and double bond unsaturation at C(20)-C(22). Digitoxigenin: 3 beta,14-Dihydroxy-5 beta-card-20(22)enolide. A cardenolide which is the aglycon of digitoxin. Synonyms: Cerberigenin; Echujetin; Evonogenin; Thevetigenin. | 14beta-hydroxy steroid; 3beta-hydroxy steroid | |
| phakellistatin 2 | phakellistatin 2: isolated from the marine sponge Phakellia carteri; structure in first source | ||
| digitoxigenin monodigitoxoside | digitoxigenin monodigitoxoside: RN given refers to (ribo-3beta,5beta)-isomer | ||
| evomonoside | evomonoside : A cardenolide glycoside consisting of digitoxigenin having an alpha-L-rhamnosyl moiety attached at the O(3)-position. evomonoside: a cytotoxic cardiac glycoside from Lepidium apetalum; RN refers to (3beta,5beta)-isomer | cardenolide glycoside | |
| halisulfate 1 | halisulfate 1: an isocitrate lyase inhibitor sesterterpene sulfate from sponge, Hippospongia sp.; structure in first source | organic molecular entity | metabolite |