Effect of intracellular potassium upon the electrogenic pump of frog retinal pigment epithelium

Summary We have studied the hyperpolarizing, electrogenic pump located on the apical membrane of the retinal pigment epithelium (RPE) in anin vitro preparation of bullfrog RPE-choroid. Changes in RPE [K⁺] _i alter the current produced by this pump. Increasing [K⁺] _o in the solution perfusing thebasal membrane increases RPE [K⁺] _i (measured with a K⁺-specific microelectrode), and also depolarizes theapical membrane. This depolarization is due to a decrease in electrogenic pump current flowing across the apical membrane resistance, since it is abolished when the pump is inhibited by apical ouabain, by cooling the tissue, or by 0mm [K⁺] _o outside the apical membrane. Removal of Cl^– from the solution perfusing the basal membrane abolishes the K⁺-evoked apical depolarization by preventing the entry of K⁺ (as KCl) into the cell. We conclude that the increase in [K⁺] _i causes the decrease in pump current. This result is consistent with the finding that [K⁺] _i is a competitive inhibitor of the Na⁺–K⁺ pump in red blood cells.It is possible that the light-evoked changes in [K⁺] _o in the distal retina could alter RPE [K⁺] _i , and thus could affect the pump from both sides of the apical membrane. Any change in pump current is likely to influence retinal function, since this pump helps to determine the composition of the photoreceptor extracellular space.     

Demonstration of afferent connections of the forebrain in Emys orbicularis turtles by the peroxidase method

The transport of horseradish peroxidase (HRP) out of the injection site in the dorsal ventricular ridge was studied in turtles Emys orbicularis. Labeled cells in the forebrain were observed in the paleostriatum among fibers of the lateral forebrain bundle. In the thalamus most of cells containing the granular HRP reaction product were located in the n. rotundus, n. reuniens and perirotundal nuclei (n. dorso-medialis anterior, n. magnocellularis thalami, n (centralis) lateralis, n. dorso-medialis). Fewer labeled cells were revealed in the n. anterior and n. ventralis. The density of labeled cells in the majority of all thalamic nuclei increased if the HRP was extended from the dorsal ventricular ridge into the neostriatum and the pallial thickening with adjacent general cortex. HRP positive cells in the pretectal area, nuclei of the posterior commissura and mesencephalic ventro-lateral tegmentum were observed only in cases when the enzyme was diffused from the injection site into the neostriatum, while the HRP retrograde transport to n. geniculatus lateralis, pars dorsalis was revealed only when HRP was extended into the pallial thickening and adjacent general cortex. Ascending connections of the paleostriatum, thalamic nuclei and mesencephalic tegmentum with telencephalic structures, mainly with the dorsal ventricular ridge, were discussed.     

A simple approach for the distribution of computationally intense tasks in an heterogeneous environment: distribution of the MDPP image-processing package

A method has been developed to link the display ability of ahigh-resolution graphics workstation with the computationalpower of a local mainframe or a remote supercomputer via anelectronic data network. The method allows this link to be establishedin a manner largely transparent to the user. The applicationof the method is illustrated by our successful distributionof the computationally intensive portions of an imaging program(MDPP) from a small VAX workstation to a VAX mainframe and CrayY-MP8/832 using a simple message-passing technique. This techniquecan be applied to almost any configuration of networked machines. Received on February 5, 1991; accepted on April 23, 1991     

Epstein-Barr Virus Polypeptides: Identification of Early Proteins and Their Synthesis and Glycosylation

We have identified at least six early polypeptides induced by Epstein-Barr virus in cells or under conditions which are nonpermissive for Epstein-Barr virus DNA replication ranging in molecular weight from 140,000 to 26,000.     

Brachiopod community paleoecology, paleobiogeography, and depositional topography of the Devonian Onondaga Limestone and correlative strata in eastern North America

The Emsian? through early Eifelian Onondaga Limestone of the Appalachian Basin was deposited in a topographic basin and on the carbonate platform which surrounded the basin on the west, north, and northeast. Onondaga strata thin from the platform into the basin. Two sedimentary cycles are present in the sub-Tioga Onondaga of eastern North America. The Edgecliff-Amherstburg represents an interval of transgression, in which epeiric seas spread over much of eastern North America. During the Nedrow-Lucas regression, the interior of the carbonate platform became restricted, resulting in the deposition of evaporites. The Moorehouse-Anderdon transgression continued through the deposition of the Tioga Bentonite, followed by the pre-Speeds-Dundee regression from the craton. Early Eifelian Appalachian Basin Onondaga brachiopod communities, arranged from nearshore to offshore, include the Atrypid-Megakozlowskiella, Atrypid-Levenea, Chonetid, Atlanticocoelia, Ambocoeliid, and Truncalosia Communities. The Onondaga-age Eastern Americas Realm is divided into the Appohimchi Province in the Appalachian Basin and the Michigan Basin-Hudson Bay Lowland Province in the Midwest. The provincial assignment of the James Bay region of Ontario is uncertain; the Eastern Townships of Quebec are near the boundaries both of the two provinces of the Eastern Americas Realm, and of the Eastern Americas Realm and the Old World Realm, the latter realm being probably in the Canadian Maritime Provinces.     

Catecholamine-Sensitive Guanylate Cyclase from Human Caudate Nucleus

Abstract: Partial purification of soluble guanylate cyclase on DEAE-Sephacel yields two separate peaks of guanylate cyclase activity. After 10-fold purification of the soluble enzyme, guanylate cyclase is markedly inhibited by micromolar concentrations of dopamine (I₅₀= 0.2 μm). Dopamine inhibition is observed whether the reaction is conducted with Mn²¹ or with Mg²⁺, under atmosphere or N₂(g), and using enzyme from either peak from the DEAESephacel column. Other catecholamines also inhibit partially purified guanylate cyclase with an order of potency at 1 μm of: dopamine =l -DOPA > norepinephrine = isoproterenol = adrenochrome > epinephrine. The structural requirements for inhibition are two free hydroxyl groups on the phenyl ring and an ethylamine side chain. Dopamine also inhibits the Triton X-100-solubilized microsomal guanylate cyclase after partial purification on DEAESephacel. Neither chlorpromazine, propranolol, nor phentolamine at 20 μm effectively block the dopamine inhibition of partially purified soluble guanylate cyclase. Micromolar concentrations of the reducing agents dithiothreitol and glutathione also inhibit partially purified guanylate cyclase, but unlike these agents, catecholamines can inhibit whether added in the reduced or the oxidized forms. Inhibition of enzyme activity by micromolar concentrations of dopamine, adrenochrome, or dithiothreitol is rapidly reversed by dilution and the dopamine inhibition is competitive with MgGTP. Inhibition does not appear to involve covalent binding or to result from the ability of catecholamines to reduce the concentrations of oxygen or free radicals in solution.     

A laboratory study on the thermal tolerance of four southeastern stream insect species (Trichoptera,Ephemeroptera)

The acute thermal tolerances of four southeastern stream insect species, Ephemerella invaria (Walker), Stenonema ithaca (Clemens and Leonard), Symphitopsyche morosa (Hagun), and Brachycentrus lateralis (Say) were determined using an artificial stream enclosure. All species were acclimated at 10°C for 72 hours prior to instantaneous immersion into heated water for 96 hours. Percent mortality was recorded and the temperature at which 50% mortality occurred determined (LT5o). Data were subjected to standard statistical analysis.Thermal tolerance values were compared between species tested and to results from previous investigations using similar methodologies. The evolution and life histories of these species were also discussed in relation to their thermal tolerance values.     

Seasonality of the rocky intertidal amphipodOligochinus lighti in response to microenvironmental variables

Organisms of intertidal regions experience climatological factors of marine and non-marine origin. Ecological studies indicate that climatological factors of non-marine origin are of primary importance in determining the distribution and abundance of the gammarid amphipodOligochinus lighti as shown by a decrease in population density with increasing height in the intertidal and a decrease in the population density accompanying seasonal increases in exposure to non-marine climatic conditions. Non-marine climatic factors affectingOligochinus are changes in temperature, salinity or moisture content in the algal clump inhabited by the amphipod. The microclimate of the algal clump depends upon its position in the intertidal and on how its form modifies the climatic conditions occurring during exposure. The algal microclimate is related in a complex fashion to seasonal changes in the coastal macroclimate mediated by the irregular semidiurnal tidal cycles of the region. A regression model has been developed to predict population changes on the basis of climatic factors.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.