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Biomedical subjects

R A Cone

Publications and source records attributed to R A Cone.

54 records · Page 3Linked to original sources
PubMed1973

Limulus rhodopsin: rapid return of transient intermediates to the thermally stable state.

Spectral transitions of rhodopsin in single cells of the Limulus ventral eye were observed both with flash photometry and by measuring the early receptor potential. Even with repetitive stimulus flashes the rhodopsin did not bleach; after each flash the spectral intermediates decayed rapidly to the initial thermally stable state. The pigment returns to the stable state in a time comparable with the duration of the late receptor potential.

Animals↗
PubMed1973

Membrane characteristics and osmotic behavior of isolated rod outer segments.

Freshly isolated frog rod outer segments are sensitive osmometers which retain their photosensitivity; their osmotic behavior reveals essentially the same light-sensitive Na(+) influx observed electrophysiologically in the intact receptor cell. Using appropriate osmotic conditions we have examined freeze-etch replicas of freshly isolated outer segments to identify the membrane which regulates the flow of water and ions. Under isosmotic conditions we find that the disc to disc repeat distance is almost exactly twice the thickness of a disc. This ratio appears to be the same in a variety of vertebrate rod outer segments and can be reliably measured in freeze-etch images. Under all our osmotic conditions the discs appear nearly collapsed. However, when the length of the outer segment is reduced by hyperosmotic shocks the discs move closer together. This markedly reduces the ratio of repeat distance to disc thickness since disc thickness remains essentially constant. Thus, the length reduction of isolated outer segments after hyperosmotic shocks primarily results from reduction of the extradisc volume. Since the discs are free floating and since they undergo negligibly small changes in volume, the plasma membrane alone must be primarily responsible for regulating the water flux and the light-sensitive Na(+) influx in freshly isolated outer segments. On this basis we calculate, from the osmotic behavior, that the plasma membrane of frog rod outer segment has a Na(+) permeability constant of about 2.8 x 10(-6) cm/s and an osmotic permeability coefficient of greater than 2 x 10(-3) cm/s.

Animals↗
PubMed1972

Dark ionic flux and the effects of light in isolated rod outer segments.

We have determined the permeability properties of freshly isolated frog rod outer segments by observing their osmotic behavior in a simple continuous flow apparatus. Outer segments obtained by gently shaking a retina are sensitive but nonideal osmometers; a small restoring force prevents them from shrinking or swelling quite as much as expected for ideal behavior. We find that Na(+), Cl(-), No(3) (-), glycerol, acetate, and ammonium rapidly enter the outer segment, but K(+), SO(4) (=), and melezitose appear impermeable. The Na flux is rectified; for concentration gradients in the physiological range, 2 x 10(9) Na(+) ions/sec enter the outer segment, but we detect no efflux of Na(+), under our conditions, when the gradient is reversed. Illumination of the outer segment produces a specific increase in the resistance to Na(+) influx, but has no effect on the flux of other solutes. This light-dependent Na(+) resistance increases linearly with the number of rhodopsin molecules bleached. We find that excitation of a single rhodopsin molecule produces a transient ( approximately 1 sec) "photoresistance" which reduces the Na(+) influx by about 1%, thus preventing the entry of about 10(7) Na(+) ions. At considerably higher light levels, a stable afterimage resistance appears which reduces the Na influx by one-half when 10(6) rhodopsin molecules are bleached per rod. We have incorporated these findings into a model for the electrophysiological characteristics of the receptor.

Acetates↗
PubMed1967

Early receptor potential: photoreversible charge displacement in rhodopsin.

When the eye is illuminated by an intense flash, the visual pigment rhodopsin begins to pass rapidly through a series of intermediate states, eventually becoming bleached. If a second flash is delivered during the lifetimes of these intermediates the rhodopsin can be photoregenerated. A fast electrical response of the visual receptors, the early receptor potential, is elicited by the first flash. A similar response is elicited by the second flash, but the polarity of this response is reversed. Moreover, this response can be separated into three components, each arising from the action of light on a different intermediate. It is likely that all these fast responses, including the early receptor potential, arise from charge displacements in the visual-pigment molecule.

Animals↗
PubMed1966

Light-stimulated electrical responses from skin.

When skin is exposed to an intense flash of light, an early electrical response can be detected from its surface. The signals that occur during the first milliseconds after the flash are similar to electrical signals recently observed in the eye from the cell layers containing melanin. Possibly the melanin in skin augments, but does not directly generate, this early electrical response. In addition, a late response, which arises hundreds of milliseconds after the flash, also occurs in skin. Unlike the early response, the late response is sensitive only to violet and shorter wavelengths of light and hence is probably mediated by a pigment other than melanin.

Animals↗
PubMedDate not supplied

Rat cauda epididymal fluid is a mucus.

Immobilin, the highly viscoelastic glycoprotein isolated from rat cauda epididymal fluid, exhibits all of the key biochemical characteristics of a mucin: 1) it has a very high molecular weight (will not pass through a 10(6) dalton cut-off filter; 2) it contains 56% carbohydrate, with low or undetectable levels of mannose, xylose and uronic acid; 3) the carbohydrates (primarily galactose, N-acetylglucosamine and N-acetylgalactosamine) are arranged in short, oligosaccharide chains (4-20 monosaccharides per chain); 4) these oligosaccharide chains can be cleaved by NaOH in the presence of NaBH4, suggesting O-glycosidic linkages; and 5) the protein core is pronase-resistant. Immobilin, however, contains no detectable sialic acid, and 67% of the oligosaccharides are uncharged, indicating that immobilin is less acidic than most other mucins.

Animals↗
PubMedDate not supplied

Using monoclonal antibodies to prevent mucosal transmission of epidemic infectious diseases.

Passive immunization with antibodies has been shown to prevent a wide variety of diseases. Recent advances in monoclonal antibody technology are enabling the development of new methods for passive immunization of mucosal surfaces. Human monoclonal antibodies, produced rapidly, inexpensively, and in large quantities, may help prevent respiratory, diarrheal, and sexually transmitted diseases on a public health scale.

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