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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 76 (1983), S. 17-26 
    ISSN: 1432-1424
    Keywords: water ; osmosis ; pressure ; Nitella ; filtration ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The hydraulic conductivity of the intracellularly-perfused internodal cell ofNitella flexilis was measured by establishing and maintaining osmotic and hydrostatic pressure gradients between the inside and the outside of the cell. The osmotic filtration coefficient (L PD ) determined at zero hydrostatic pressure difference varied between 1.55 and 2.32×10−5 cm/sec/atm. Under internal perfusion conditions no polarity between endosmotic and exosmotic flow was observed. The overall hydrostatic filtration coefficient (L P ) was determined with a step change in hydrostatic pressure up to 0.2 atm, while the osmotic pressure difference was maintained at zero.L P was considerably greater than theL PD , i.e., 14.1 to 19.2×10−5 cm/sec/atm. Theoverall L P of such internodes, which showed protoplasmic streaming and action potentials was the same as that of the isolated cell walls, the latter being 13.2 to 19.9×10−5 cm/sec/atm. Some of these results are consistent with previous results onNitella using different techniques. The situation inNitella where at abnormallylow internal pressure the barrier to hydrostatic pressure-driven water flow does not reside in the plasmalemma but in an in-series structure is comparable to that in the squid axon where the normal internal pressure is close to zero. An interpretation is offered for the finding in the alga that athigh internal pressures the plasmalemma becomes the rate-limiting structure for hydrostatic pressure-driven water flow. It is suggested that the internal pressure pushes a large fraction of the plasmalemma against skeletal nonporous regions of the cell wall. This suggestion entailing a pressure-dependent cell wall-plasmalemma juxtaposition was also deployed in interpreting previous observations in plant cells on water flow polarity (i.e., observations showing that exosmotic rates are less than endosmotic).
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 47 (1979), S. 195-238 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A previous method of measuring the swelling pressure (ΔΠ g ) of the cytoplasmic gel of the giant axon ofLoligo vulgaris was refined. The estimates ofΔΠ g made with the improved method were consistent with those made with the earlier method. In these methods the activity of the solvent in the gel is measured by increasing the activity of the solvent in the internal phase of the gel by application of hydrostatic pressure to the gel directly. Comparable values for the activity of the solvent in the gel were obtained also by an alternate method, in which the deswelling of the gel is measured upon decreasing the activity of the solvent in the external phase by addition of a nonpenetrating high mol wt polymer (i.e., Ficoll). Additional support was obtained for the earlier suggestion thatΔΠ g contributes to the swelling and shrinkage pattern of the whole axon. In part, the new evidence involved two consecutivedirect measurements of intraxonal pressure. The first measurement was that of a mixed pressure composed ofΔΠ g andΔΠ m (ΔΠ m being the effective osmotic pressure due to the intra-extraxonal gradient in the activity of mobile solutes). The subsequent measurement was that ofΔΠ g alone. The latter measurement was made feasible by destroying the axolemma, thereby eliminating the contribution ofΔΠ m . An estimate ofΔΠ m was obtained by subtractingΔΠ g from the total pressure measured initially. TheΔΠ m determined by the above method was two orders of magnitude smaller than the theoretical osmotic pressure. This is consistent with theΔΠ m determined previously, where osmotic intra-extraxonal filtration coefficients were compared to the hydrostatic. The mixed pressure experiments lend credence to the idea that the substantial contribution ofΔΠ g to the water relations of the whole axon is due toΔΠ g being of the same order of magnitude asΔΠ m . The degree of free swelling of axoplasmic gels was studied as a function of pH, salt concentration, and hydration radius of the anion of the salt used. The swelling increased with an increase in the reciprocal of the hydration radius, a decrease in salt concentration, and at pH below or above ∼4.5. The nature of the constraints to the free swelling of axoplasm in axons immersed in seawater was studied. With the seawater employed, these constraints appeared to be due more to the retractive forces of the sheath than toΔΠ m .
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 32 (1977), S. 1-18 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The hydrostatic (L p ) and osmotic (L PD ) filtration coefficients and the efflux rates of tritiated water were measured in the giant axon ofLoligo vulgaris. TheL p was 8 to 14×10−8 cm/sec/cm H2O and theL PD was two orders of magnitude smaller (3 to 6×10−10 cm/sec/cm H2O). In axons whose diameter was ∼500 μ, the time (t 1/2) required for a reduction in the axonal labeled water activity to one half its initial value was 38 to 48 sec. The rate limiting structure for solute flux was made ineffective by (1) storing the axon in isosmotic KF at 0–2 °C for one month to one year or by (2) fixing the axon in 2–4% glutaraldehyde for 3 to 7 hr. The criteria of ineffectiveness of the rate limiting structure for solute flux were (1) a reduction ofL PD to immeasurably low values, (2) the absence of electrical properties characteristic of a plasmalemma, and (3) a marked increase in the rate of efflux of Na22. In such impaired axons theL p and thet 1/2 of tritiated water efflux were unaffected. This independence of solute and solvent flux in conjunction with the finding that the hydraulic conductivity determined by bulk osmotic and hydrostatic pressure gradients is not equivalent (i.e.,L PD /L P ≪1) indicate that the rate limiting structures for solute and solvent flux are in series. Solvent fluxes appear to be surface-limited, not bulk-limited. We have been unable to resolve whether the surface structure involved in limiting solvent flux is the sheath (Schwann layer and adhering connective tissue) and/or the cortical layer of the axoplasmic gel.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 32 (1977), S. 19-32 
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The volumetric elastic modulus of the sheath and the osmotic swelling pressure of the axoplasmic polymer network of the giant axon ofLoligo vulgaris were measured. Evidence was obtained that (1) the elastic modulus of the sheath, (2) the swelling pressure of axoplasm, and (3) theeffective osmotic pressure difference due to mobile solutes determine axonal volume. The contributions of the sheath and the axoplasm were significant because theeffective osmotic pressure due to mobile solutes was a small fraction of thetheoretical bulk osmotic pressure due to these solutes. The giant axon was converted from an imperfect to a near perfect osmometer by minimizing the contribution of the sheath and the axoplasmic gel.
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  • 5
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 22 (1960), S. 407-432 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 63 (1967), S. 72-75 
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 1968-05-01
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 8
    Publication Date: 1960-03-01
    Print ISSN: 0066-4278
    Electronic ISSN: 1545-1585
    Topics: Biology , Medicine
    Published by Annual Reviews
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  • 9
    Publication Date: 1959-05-15
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 1961-06-30
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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