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  • 1
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    A multifunctional aqueous channel formed by CFTR (1992)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1992-11-27
    Description: The cystic fibrosis gene product (CFTR) is a complex protein that functions as an adenosine 3,5-monophosphate (cAMP)-stimulated ion channel and possibly as a regulator of intracellular processes. In order to determine whether the CFTR molecule contains a functional aqueous pathway, anion, water, and urea transport were measured in Xenopus oocytes expressing CFTR. Cyclic AMP agonists induced a Cl- conductance of 94 microsiemens and an increase in water permeability of 4 x 10(-4) centimeter per second that was inhibited by a Cl- channel blocker and was dependent on anion composition. CFTR has a calculated single channel water conductance of 9 x 10(-13) cubic centimeter per second, suggesting a pore-like aqueous pathway. Oocytes expressing CFTR also showed cAMP-stimulated transport of urea but not the larger solute sucrose. Thus CFTR contains a cAMP-stimulated aqueous pore that can transport anions, water, and small solutes. The results also provide functional evidence for water movement through an ion channel.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hasegawa, H -- Skach, W -- Baker, O -- Calayag, M C -- Lingappa, V -- Verkman, A S -- DK35124/DK/NIDDK NIH HHS/ -- DK43840/DK/NIDDK NIH HHS/ -- HL42368/HL/NHLBI NIH HHS/ -- etc. -- New York, N.Y. -- Science. 1992 Nov 27;258(5087):1477-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Medicine, University of California, San Francisco 94143-0532.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1279809" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Base Sequence ; Biological Transport/physiology ; Chlorides/metabolism ; Cyclic AMP/physiology ; Cystic Fibrosis Transmembrane Conductance Regulator ; Female ; Humans ; In Vitro Techniques ; Ion Channels/*physiology ; Membrane Proteins/*physiology ; Molecular Sequence Data ; Oocytes ; Urea/metabolism ; Water/metabolism ; Xenopus
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Venusian sinuous rilles (1992)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: After a preliminary assessment of venusian channels, it now seems to be clear that the channels have distinctive classes, which imply a wide range of formation parameters and formation mechanisms. They include outflow channels mainly formed by mechanical erosion from very high discharge flow, and canali-type channels requiring either constructional process or mechanical erosion by rather exotic low-viscosity lava such as carbonatite or sulfur. Here we focus on venusian sinuous rilles. Venusian sinuous rilles are generally simple, and originate from a collapsed source. They are shallow and narrow downstream. The venusian sinuous rilles are distinct from canali-type channels, which exhibit almost constant morphologies throughout their entire length, and from outflow channels, which are characterized by wide anastomosing reaches. The lunar sinuous rilles could have been formed initially as constructional channels. However, incision was caused by the long flow duration and high temperatures of eruption, along with relatively large discharge rates, possibly assisted by a low viscosity of the channel-forming lava. Channel narrowing and levee formation suggest relatively fast cooling. The venusian channels could have had a similar sequence of formation including rapid cooling. Assuming the substrate is typical tholeiitic lava, the flowing lavas' temperatures have to be higher than the melting temperature of the substrate. The flow should have a low viscosity to cause turbulence and keep a high Reynolds number to sustain efficient thermal erosion. Determining eruption conditions also provide insights to estimate lava composition. Assuming a channel is formed mostly by thermal erosion, the channel's length and longitudinal profile are functions of lava properties. The depth profiles of the channel are measured by radar foreshortening methods and stereo images. Eruption conditions of channel forming lava can be estimated by the methods developed by Hulme.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 60-61
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  • 3
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    Channels and valleys on Venus - Preliminary analysis of Magellan data (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A preliminary survey of Magellan imagery reveals more than 200 newly discovered relic channel and valley landform complexes. For purposes of discussion the channels can be classed as simple, complex, and compound. Integrated valleys also occur. Simple channels include: (1) sinuous rilles that closely resemble their lunar counterparts and (2) a newly recognized long sinuous form of high width-to-depth ratio and remarkably constant width. Herein designated canali, the most spectacular of these channels is 6800 km long. One of the compound channels, an outflow complex in Lada Terra, extends over 1200 km and is up to 30 km wide. Streamlined hills and spill relationships at a cross-axial ridge are similar to features in flood channels. Venusian channels have a global distribution with most of the large canali-type channels developed on volcanic plains. Alternative hypotheses for the channel-forming processes include genesis by the following erosive fluids: ultramafic silicate melts, sulfur, and carbonate lavas. Each of these causative agents has profound implications for Venusian planetology. The remote possibility of an aqueous origin, indicated by apparent regime behavior of the active channeling process, cannot be excluded with absolute certainty.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; E8 A; 13
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  • 4
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    Subsurface emissions from Mercury - VLA radio observations at 2 and 6 centimeters (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Radio observations of Mercury made with the VLA; once in 1986, and on two dates in February of 1988 are presented. These observations are the first to spatially map both hot regions associated with the theoretical hot poles. These 'hot poles' are separated by 180 deg and are a result of the unusual diurnal heating from Mercury's 3/2 spin-orbit resonance and eccentric orbit. The highest resolution data maps areas of the planet as small as 330 km. Maps of total intensity, brightness temperature, polarized intensity, fractional polarization, depolarization, and spectral index are included. It is found that the subsurface thermal emissions from Mercury are characteristic of blackbody reradiation from the solar insolation over a diurnal cycle. These observations to produce full-disk thermophysical models are used. The one-dimensional, time-dependent heat-diffusion equation for all observed disk elements at each epoch in order to constrain thermophsyical parameters and properties of the subsurface material are solved. Using typical lunar values for several of the parameters, it is possible to reproduce the temperature morphology and most of the observed temperature values. It is found that the best-fit models require a substantial contribution of the heat transport in the subsurface to be radiative in nature. The primary difficulty in the models is in predicting the observed temperature differences as a function of frequency.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 384; 640-655
    Format: text
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  • 5
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    Channels and valley networks (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Attention is given to Martian channels and valley networks, since they have become a principal element of evidence to the effect that the Martian atmosphere evolved from an early volatile-rich state to its present condition. The outflow channels are relatively young, later Hesperian or Amazonian in age. They formed by immense outbursts of fluid from subsurface sources. Complexity in outflow-channel morphology was generated by varying amounts of sediment and ice in the aqueous-fluid flow systems. The overall cataclysmic-flood morphology may thus be locally transitional to morphologies generated by ice and debris flowage. Although local areas of valley networks, such as on Alba Patera, formed coevally with outflow channel activity, regionally extensive networks dominate in the heavily cratered terrains. The morphology of many valleys suggests genesis by ground-water sapping; for some valleys, surface runoff may have been more important.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 493-522.
    Format: text
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  • 6
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    Cellular convection in the atmosphere of Venus (1992)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: Among the most intriguing feature of the atmosphere of Venus is the presence of cellular structures near and downwind of the subpolar point. It has been suggested that the structures are atmospheric convection cells, but their breadth and thinness would pose a severe challenge to the dynamics of convection. It is proposed here that strongly penetrative convection into the stable regions above and below the neutrally stable cloud layer coupled with penetrative convection from the surface increases the vertical dimensions of the cells, thereby helping to explain their large horizontal extent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 355; 710-712
    Format: text
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  • 7
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    Canali-type channels on Venus - Some genetic constraints (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Canali-type channels on Venus are unique because of their great lengths (up to 6800 km) and nearly constant channel cross sectional shapes along their paths. A simple model incorporating channel flow and radiative cooling suggests that common terrestrial-type tholeiite lava cannot sustain a superheated and turbulent state for the long distances required for thermal erosion of canali within allowable discharge rates. If canali formed mainly by constructional processes, laminar tholeiitic flow of relatively high, sustained discharge rates might travel the observed distances, but the absence of levees would need to be explained. An exotic low temperature, low viscosity lava like carbonatite or sulfur seems to be required for the erosional genesis of canali.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 13 J; 1415-141
    Format: text
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