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K G Pote

Publications and source records attributed to K G Pote.

13 recordsLinked to original sources
PubMed1993

Otoconin-22, the major protein of aragonitic frog otoconia, is a homolog of phospholipase A2.

Otoconia are composites of proteins and inorganic crystals formed in the peripheral portion of the vestibular system of vertebrates. They add mass to the extracellular otoconial membrane, thereby increasing its deflection during linear acceleration. This added mass increases the sensitivity of the underlying sensory maculae. Otoconia provide a promising system to decipher the interaction of protein and mineral during the growth and maintenance of biominerals. We have purified the major protein of the aragonitic otoconia of Xenopus laevis, which we call otoconin-22, and determined its amino acid sequence and carbohydrate composition. The 127 residues are 37% identical to the phospholipase A2 from Crotalus atrox. We propose that otoconin-22 from X. laevis is homologous to phospholipase A2 and has a similar tertiary structure.

Amino Acid Sequence↗
PubMed1993

Inferred protein content and distribution from density measurements of calcitic and aragonitic otoconia.

Otoconia from the peripheral portion of the vestibular system contain specific proteins and are mineralized by several polymorphs of calcium carbonate. To infer the internal distribution of their mineral and protein components, we have measured the densities, by equilibrium centrifugation, and the lengths of aragonitic otoconia from the African clawed frog (Xenopus laevis) and calcitic otoconia from the Norway rat (Rattus norvegicus). The densities are statistically dependent on the length of the otoconia. Further, this dependence is not the same for aragonitic and calcitic otoconia. Aragonitic otoconia are statistically more dense when smaller and less dense when larger. For calcitic otoconia the opposite is true; the smaller otoconia are statistically less dense than larger otoconia. Because the organic and inorganic phases have different densities, this indicates that the otoconial proteins and the mineral phases have different distributions within these two types of otoconia.

Animals↗
PubMed1993

Utricular otoconia of some amphibians have calcitic morphology.

This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics calcite, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.

Ambystoma mexicanum↗
PubMed1991

Each otoconia polymorph has a protein unique to that polymorph.

1. Otoconia, contained within the vestibular portion of the inner ear, are mineralized by one of three polymorphs of calcium carbonate. Each otoconial polymorph contains a unique, major protein. 2. The major protein of calcitic otoconia of members of different vertebrate classes, Amphibia (African clawed frog) and Mammalia (rat), have similar molecular weights. 3. The major protein of calcitic rat otoconia and of vateritic otoconia of the gar may be calcium binding proteins. No protein from the other polymorph, aragonite, appear to have this characteristic.

Ambystoma mexicanum↗
PubMed1984

Some properties of otoconia.

Otoconia are dynamic mineral deposits present in the gravity receptors of most vertebrates; fishes often have a single large mass called an otolith instead. Otoconia generally have the appearance of single crystals but contain organic and inorganic components, the mineral being almost exclusively a polymorph of calcium carbonate. The two phases are closely interrelated structurally. Ultra-high resolution transmission electron microscopy of rat otoconia showed them to be mosaic biominerals. The crystallites were 50-100 nm in diameter, had some rounded edges, and were highly ordered into laminae. This suggests that crystallite seeding and growth is organic matrix mediated. Crystallite asymmetry may also indicate piezoelectricity. A further finding of similarities in electron beam diffraction patterns obtained from some frog and rat otoconia could mean that the calcite of mammalian units mimics aragonite. A comparative study showed that turtles, which are close to the stem line for mammals, had calcite-type otoconia in the utricle. Alligators, which share a common ancestry with birds, had this type otoconium in all three gravity receptors, although saccular otoconia had a variety of forms. The nature of the mineral is unknown. The biochemical composition of the organic otoconial material is under study, to learn how mineral deposition is regulated. Proteins of rat otoconial complexes ranged between ca. 16500 and over 100000 Da in molecular mass and were similar in saccular and utricular otoconial complexes. Our new analysis of the amino acid composition of the complexes by high performance liquid chromatography showed the complexes to be high in the acidic and low in the basic amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Alligators and Crocodiles↗
PubMed1984

Developmental changes in the neutral alpha-amino acid transport systems of rat brain over the first three weeks after birth.

Transport of seven different amino acids into brain slices increased as donor rats aged from 1 to 6 days. Uptakes of 2-aminoisobutyric acid, 2-(methyl-amino)isobutyric acid, and L-alanine then decreased by day 14, while uptakes of other amino acids continued to increase or remained fairly constant. Neutral alpha-amino acid transport systems were characterized by measuring inhibition of uptakes and kinetics for representative amino acids at different ages. Results indicate that 2-aminoisobutyrate and 2-(methylamino)isobutyrate used only one (and the same) system in brain slices from 6-day-old rats, with characteristics of system A (the major sodium-dependent system in most mammalian cells). They used at least two systems at ages 1, 14, and 23 days, but, of these, only at 1 day did they use the same systems in the same proportions. Alanine and leucine used more than one system at all four ages, and somewhat different combinations than used by each other or by 2-aminoisobutyrate or 2-(methylamino)isobutyrate. Their transport characteristics showed they used mostly system ASC (a sodium-dependent system distinguished from A) and/or system L (sodium-independent). We conclude that system A increases as the brain ages from 1 to 6 days and declines thereafter. System L probably increases with aging from 1 to 23 days.

Aging↗
PubMed1984

Thyroxine-induced changes in the development of neutral alpha-amino acid transport systems of rat brain.

Transport of representative neutral alpha-amino acids was measured in brain slices after injecting thyroxine into donor rats of various ages from 1 to 23 days old. The hormone did not alter uptake in slices from 1-day-old rats even when treatment was begun on pregnant rats as much as 10 days before delivery. Injecting thyroxine until age 6 days, however, decreased the activity of transport system A (the major sodium-dependent system in most mammalian cells) and caused appearance of a new transport system used by the model amino acids, 2-aminoisobutyric acid and 2-(methylamino)isobutyric acid. Uptake at 6 days was similar to that found in slices from older, untreated rats (e.g., those 14 days old). These results strongly suggest that one action of thyroxine is to accelerate the development of neutral alpha-amino acid transport systems of brain over the first six days after birth. Thyroxine treatment of rats from birth to age 14 days also appears to increase the activities of both system A and the second transport system used by the two model amino acids in brains from 14-day-old rats.

Aging↗
PubMedDate not supplied

Ultrastructural morphology and protein content of the internal organic material of rat otoconia.

Otoconia taken from the maculae of the saccule and utricle of the rat inner ear were investigated using transmission electron microscopy (TEM). Their ultrastructure was compared using various decalcification techniques. Similar preparations were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to assess their protein constituents. TEM results show loss of organic material during prolonged decalcification. This is not seen in samples decalcified overnight. The SDS-PAGE results show that rat otoconia contain a major broad band of 90-100 kDa, a major thin band of 56 kDa, and three other bands of 33, 45, and 50 kDa. The band of 56 kDa may be associated with the surface of the otoconia.

Animals↗
PubMedDate not supplied

Macular suprastructure, stereociliary bonding and kinociliary/stereociliary coupling in rat utricular macula.

This report considers rat utricular macular suprastructure after chemical treatment with the sodium salt of N,N-Naphthaloylhydroxylamine (NHA), used alone or in combination with tannic acid (TA). NHA and TA preserve calcium and complex carbohydrate-protein molecules, respectively. Macromolecules of supramacular substance appear comparable morphologically to material of the external lamina of glycocalyx. Similar material crosslinks stereocilia with approximately equal to 58 nm periodicity and couples parts of kinocilia with specific stereocilia. Particles which occur within kinocilia at certain attachment sites connect to dynein arms of the kinocilia. Interstereociliary connections are aligned with internal linkers to actin. Thus, a basis for dynamic communication between kinocilia and stereociliary actin has been shown. The mechanism would appear to be calcium dependent. The findings support the concept that kinocilia are motile and lead to the stereociliary tuft in vestibular hair cells.

Animals↗
PubMedDate not supplied

The suprastructure of the saccular macula.

Inclusion of tannic acid in the primary fixative fortuitously preserved the macular suprastructure, from the macular surface to the otoconia, in rat. Results demonstrate that fluid-filled channels around the stereociliary tufts and a slit-like space immediately above the macula are artefacts of tissue preparation. Filaments fill the area between, and show linkage to, the macular surface and the more peripheral, closely knit layer identified here as the true otoconial membrane. The material also passes through the otoconial membrane at various sites to surround the otoconia and extends well beyond the maculas in all directions. Although it may prove later to be endolymph, it is referred to here as supramacular substance. Kinocilia and the tallest stereocilia as well as the otoconia are tethered to the otoconial membrane. Findings were confirmed in decalcified material. Results are discussed in terms of functional and biochemical implications, and by analogy to man-made acceleration sensing devices.

Animals↗