Biomaterial Database

External calcium inhibits the efflux of calcium from isolated retinal rod outer segment disks. 1985

H G Smith, and P M Capalbo

Increasing the concentration of calcium in the external buffer flowing past isolated, intact bovine retinal rod outer segment disks immobilized in a flow system reduced the rate of radioactive calcium efflux from within the disks in the dark. We interpret these results as extradiskal calcium acting at an inhibitory binding site to block the calcium efflux. A Scatchard analysis of the external calcium dependence of the efflux yields an apparent dissociation constant of 50 microM, which further suggests that the inhibition is mediated by a specific membrane binding site. The observed inhibition of calcium efflux may represent a functional role for the high-affinity calcium binding site which has been identified by others in previous physical studies of the disk membrane. This external calcium inhibited permeability may explain some of the discrepancies in the reported calcium transport properties of disks. Variations in the external calcium concentration may alter the calcium content of isolated disks, thereby indirectly affecting other transport functions including the measured light-induced release of calcium. No evidence was found for either Na/Ca or Ca/Ca exchange processes across the disk membrane. Lanthanum was even more effective than calcium in inhibiting calcium efflux in the dark. Neither lanthanum nor calcium inhibited the light-induced efflux of calcium from disks, which implies either that light and extradiskal calcium regulate separate permeability processes in the disk membrane or that light greatly reduces the affinity of the inhibitory site for calcium and lanthanum.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D007811	Lanthanum	The prototypical element in the rare earth family of metals. It has the atomic symbol La, atomic number 57, and atomic weight 138.91. Lanthanide ion is used in experimental biology as a calcium antagonist; lanthanum oxide improves the optical properties of glass.
D008027	Light	That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.	Light, Visible,Photoradiation,Radiation, Visible,Visible Radiation,Photoradiations,Radiations, Visible,Visible Light,Visible Radiations
D010786	Photoreceptor Cells	Specialized cells that detect and transduce light. They are classified into two types based on their light reception structure, the ciliary photoreceptors and the rhabdomeric photoreceptors with MICROVILLI. Ciliary photoreceptor cells use OPSINS that activate a PHOSPHODIESTERASE phosphodiesterase cascade. Rhabdomeric photoreceptor cells use opsins that activate a PHOSPHOLIPASE C cascade.	Ciliary Photoreceptor Cells,Ciliary Photoreceptors,Rhabdomeric Photoreceptor Cells,Rhabdomeric Photoreceptors,Cell, Ciliary Photoreceptor,Cell, Photoreceptor,Cell, Rhabdomeric Photoreceptor,Cells, Ciliary Photoreceptor,Cells, Photoreceptor,Cells, Rhabdomeric Photoreceptor,Ciliary Photoreceptor,Ciliary Photoreceptor Cell,Photoreceptor Cell,Photoreceptor Cell, Ciliary,Photoreceptor Cell, Rhabdomeric,Photoreceptor Cells, Ciliary,Photoreceptor Cells, Rhabdomeric,Photoreceptor, Ciliary,Photoreceptor, Rhabdomeric,Photoreceptors, Ciliary,Photoreceptors, Rhabdomeric,Rhabdomeric Photoreceptor,Rhabdomeric Photoreceptor Cell
D002021	Buffers	A chemical system that functions to control the levels of specific ions in solution. When the level of hydrogen ion in solution is controlled the system is called a pH buffer.	Buffer
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D002417	Cattle	Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.	Beef Cow,Bos grunniens,Bos indicus,Bos indicus Cattle,Bos taurus,Cow,Cow, Domestic,Dairy Cow,Holstein Cow,Indicine Cattle,Taurine Cattle,Taurus Cattle,Yak,Zebu,Beef Cows,Bos indicus Cattles,Cattle, Bos indicus,Cattle, Indicine,Cattle, Taurine,Cattle, Taurus,Cattles, Bos indicus,Cattles, Indicine,Cattles, Taurine,Cattles, Taurus,Cow, Beef,Cow, Dairy,Cow, Holstein,Cows,Dairy Cows,Domestic Cow,Domestic Cows,Indicine Cattles,Taurine Cattles,Taurus Cattles,Yaks,Zebus
D002463	Cell Membrane Permeability	A quality of cell membranes which permits the passage of solvents and solutes into and out of cells.	Permeability, Cell Membrane
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D012374	Rod Cell Outer Segment	The portion of a retinal rod cell situated between the ROD INNER SEGMENT and the RETINAL PIGMENT EPITHELIUM. It contains a stack of photosensitive disk membranes laden with RHODOPSIN.	Rod Outer Segment,Rod Outer Segments,Outer Segment, Rod,Outer Segments, Rod