Direct measurements of sieve element hydrostatic pressure reveal strong regulation after pathway blockage

2004 ◽  
Vol 31 (10) ◽  
pp. 987 ◽  
Author(s):  
Nick Gould ◽  
Peter E. H. Minchin ◽  
Michael R. Thorpe
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Sucrose Concentration ◽  
Turgor Pressure ◽  
Sieve Tube ◽  
Pressure Regulation ◽  
Solution Flow ◽  
Hydrostatic Pressure Gradient ◽  
Flow Through

According to the Münch hypothesis, solution flow through the phloem is driven by a hydrostatic pressure gradient. At the source, a high hydrostatic pressure is generated in the collection phloem by active loading of solutes, which causes a concomitant passive flow of water, generating a high turgor pressure. At the sink, solute unloading from the phloem keeps the turgor pressure low, generating a source-to-sink hydrostatic pressure gradient. Localised changes in loading and unloading of solutes along the length of the transport phloem can compensate for small, short-term changes in phloem loading at the source, and thus, maintain phloem flow to the sink tissue. We tested directly the hydrostatic pressure regulation of the sieve tube by relating changes in sieve tube hydrostatic pressure to changes in solute flow through the sieve tube. A sudden phloem blockage was induced (by localised chilling of a 1-cm length of stem tissue) while sieve-tube-sap osmotic pressure, sucrose concentration, hydrostatic pressure and flow of recent photosynthate were observed in vivo both upstream and downstream of the block. The results are discussed in relation to the Münch hypothesis of solution flow, sieve tube hydrostatic pressure regulation and the mechanism behind the cold-block phenomenon.

scholarly journals Electromyography of the Respiratory Muscles and Gill Water Flow in the Dragonet

1968 ◽  
Vol 49 (3) ◽  
pp. 583-602
Author(s):  
G. M. HUGHES ◽  
C. M. BALLINTIJN
Keyword(s):  
Hydrostatic Pressure ◽  
Stroke Volume ◽  
Pressure Gradient ◽  
Time Course ◽  
Respiratory Muscles ◽  
Adverse Pressure Gradient ◽  
Pressure Head ◽  
Volume Flow ◽  
Frequency Change ◽  
Hydrostatic Pressure Gradient

1. An account is given of the main skeletal elements and muscles involved in the respiratory movements of the dragonet, Callionymus lyra. 2. Using electromyographic techniques it has been shown that the muscles chiefly involved in rapid ejection of water out of the opercular slit are the adductor mandibulae, protractor hyoideus, and hyohyoideus. During the expansion phase of the cycle, which is about six times the duration of the contraction phase, the levator hyomandibulae and sternohyoideus are active, though in some cases the latter only comes in at higher levels of pumping. 3. Changes in volume flow across the gills have been produced by either (a) altering the hydrostatic pressure gradient (Δp) across the system, or (b) altering the oxygen or carbon dioxide content of the water inspired by the fish. With (a), the volume flow decreases linearly at a rate of about 30 ml./min./cm. H2O static pressure head until an inflexion is reached in the curve at which rate of flow decreases and is normally when Δp is zero. That the relative increase in flow rate with negative Δp's is due to the activity of the fish pumping against the adverse pressure gradient has been confirmed by electromyogram recordings during such experiments. With (b), it was possible to demonstrate a clear relationship between stroke volume and the level of electrical activity as measured by the height of the integrated electromyogram. The integrated EMG increases more than linearly with increasing stroke volume during PO2 changes, but this relationship seems to be more nearly linear during changes in CO2 concentration. 4. The respiratory frequency is scarcely affected by changes in flow produced by altering the hydrostatic pressure gradient, but following a decrease in PO2 or an increase in CO2 there is a significant fall in frequency which accompanies the increased electromyogram. The time course of these changes during recovery from a decrease in PO2 or an increase in PCOCO2 suggests that the gas tensions of the inspired water are detected by receptors on the gills and thus influence the electromyogram activity, but the frequency change observed is due to a change in the blood affecting receptors in the brain.

A cloned renal epithelial Na+ channel protein displays stretch activation in planar lipid bilayers

1995 ◽  
Vol 268 (6) ◽  
pp. C1450-C1459 ◽  
Author(s):  
M. S. Awayda ◽  
I. I. Ismailov ◽  
B. K. Berdiev ◽  
D. J. Benos
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Na Channel ◽  
Planar Lipid Bilayers ◽  
Stretch Activation ◽  
Hydrostatic Pressure Gradient ◽  
Epithelial Na Channel

We have previously cloned a bovine renal epithelial channel homologue (alpha-bENaC) belonging to the epithelial Na+ channel (ENaC) family. With the use of a rabbit nuclease-treated in vitro translation system, mRNA coding for alpha-bENaC was translated and the polypeptide products were reconstituted into liposomes. On incorporation into planar lipid bilayers, in vitro-translated alpha-bENaC protein 1) displayed voltage-independent Na+ channel activity with a single-channel conductance of 40 pS, 2) was mechanosensitive in that the single-channel open probability was maximally activated with a hydrostatic pressure gradient of 0.26 mmHg across the bilayer, 3) was blocked by low concentrations of amiloride [apparent inhibitory constant of amiloride (K(i)amil approximately 150 nM], and 4) was cation selective with a Li+:Na+:K+ permselectivity of 2:1:0.14 under nonstretched conditions. These pharmacological and selectivity characteristics were altered to a lower amiloride affinity (K(i)amil > 25 microM) and a lack of monovalent cation selectivity in the presence of a hydrostatic pressure gradient. This observation of stretch activation (SA) of alpha-bENaC was confirmed in dual electrode recordings of heterologously expressed alpha-bENaC whole cell currents in Xenopus oocytes swelled by the injection of 15 nl of a 100 mM KCl solution. We conclude that alpha-bENaC, and by analogy other ENaCs, represent a novel family of cloned SA channels.

scholarly journals Role of a Hydrostatic Pressure Gradient in the Formation of Early Ischemic Brain Edema

1986 ◽  
Vol 6 (5) ◽  
pp. 546-552 ◽  
Author(s):  
Shizuo Hatashita ◽  
Julian T. Hoff
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Water Content ◽  
Brain Edema ◽  
Intraluminal Pressure ◽  
Tissue Pressure ◽  
Ischemic Brain ◽  
Hydrostatic Pressure Gradient ◽  
Arterial Blood ◽  
Ischemic Brain Edema

We studied whether a hydrostatic pressure gradient between arterial blood and brain tissue plays a role in the formation of early ischemic cerebral edema after middle cerebral artery (MCA) occlusion in cats. Tissue pressure, regional CBF, and water content were measured from the cortex in the core and the peripheral zone of brain normally perfused by the MCA. Intraluminal arterial pressure was altered at intervals by inflation of an aortic balloon to vary the blood–tissue pressure gradient in the ischemic zone. Brain water content in the ischemic core, where flow fell to 5.5 ml/100 g/min, increased within 1 h of occlusion. After occlusion tissue pressure rose from 7.95 ± 0.72 mm Hg at 1 h to 13.16 ± 1.13 mm Hg at 3 h. When intraluminal pressure was increased, water content increased further, but only at 1 h after occlusion. In the periphery where flow was 18.9 ml/100 g/min during normotension. neither water content nor tissue pressure rose within 3 h of occlusion. Increased intraluminal pressure was accompanied by increased water content only at 3 h. This study indicates that a hydrostatic pressure gradient is an important element in the development of ischemic brain edema, exerting its major effect during the initial phase of the edema process.

In vivo hydraulic conductivity of muscle: effects of hydrostatic pressure

1997 ◽  
Vol 273 (6) ◽  
pp. H2774-H2782 ◽  
Author(s):  
El Rasheid Zakaria ◽  
Joanne Lofthouse ◽  
Michael F. Flessner
Keyword(s):  
Hydrostatic Pressure ◽  
Hydraulic Conductivity ◽  
Pressure Gradient ◽  
Abdominal Wall ◽  
Peritoneal Cavity ◽  
Interstitial Pressure ◽  
Fluid Flux ◽  
Reduced Pressure ◽  
Local Loss

We and others have shown that the loss of fluid and macromolecules from the peritoneal cavity is directly dependent on intraperitoneal hydrostatic pressure (Pip). Measurements of the interstitial pressure gradient in the abdominal wall demonstrated minimal change when Pipwas increased from 0 to 8 mmHg. Because flow through tissue is governed by both interstitial pressure gradient and hydraulic conductivity ( K), we hypothesized that K of these tissues varies with Pip. To test this hypothesis, we dialyzed rats with Krebs-Ringer solution at constant Pipof 0.7, 1.5, 2.2, 3, 4.4, 6, or 8 mmHg. Tracer amounts of125I-labeled immunoglobulin G were added to the dialysis fluid as a marker of fluid movement into the abdominal wall. Tracer deposition was corrected for adsorption to the tissue surface and for local loss into lymphatics. The hydrostatic pressure gradient in the wall was measured using a micropipette and a servo-null system. The technique requires immobilization of the tissue by a porous Plexiglas plate, and therefore a portion of the tissue is supported. In agreement with previous results, fluid flux into the unrestrained abdominal wall was directly related to the overall hydrostatic pressure difference across the abdominal wall (Pip= 0), but the interstitial pressure gradient near the peritoneum increased only ∼40% over the range of Pip= 1.5–8 mmHg (20–28 mmHg/cm). K of the abdominal wall varied from 0.90 ± 0.1 × 10−5cm2⋅ min−1⋅ mmHg−1at Pip= 1.5 mmHg to 4.7 ± 0.43 ×10−5cm2⋅ min−1⋅ mmHg−1on elevation of Pipto 8 mmHg. In contrast, for the same change in Pip, abdominal muscle supported on the skin side had a significantly lower range of fluid flux (0.89–1.7 × 10−4vs. 1.9–10.1 × 10−4ml ⋅ min−1⋅ cm−2in unsupported tissue). The differences between supported and unsupported tissues are likely explained in part by a reduced pressure gradient across the supported tissue. In conclusion, the in vivo hydraulic conductivity of the unsupported abdominal wall muscle in anesthetized rats varies with the superimposed hydrostatic pressure within the peritoneal cavity.

Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments

1987 ◽  
Vol 14 (4) ◽  
pp. 397 ◽  
Author(s):  
PEH Minchin ◽  
MR Thorpe
Keyword(s):  
Hydrostatic Pressure ◽  
Phaseolus Vulgaris ◽  
Pressure Gradient ◽  
Phloem Transport ◽  
Pressure Chamber ◽  
Supporting Evidence ◽  
Hydrostatic Pressure Gradient

A pressure chamber was used to increase suddenly the hydrostatic pressure in the upper shoot of a Phaseolus vulgaris plant while observing phloem transport of 11C-labelled photoassimilate. Phloem transport in the stem towards the chamber stopped immediately when pressure was applied and then recovered within about 5 min. If the pressure was then released, flow increased again. The results support the hypothesis that flow of photoassimilate in the stem phloem was driven by a hydrostatic pressure gradient.

Laterally accreting sinuous channels and their deposits: The Goldilocks of deep-water slope systems

2021 ◽  
Vol 91 (5) ◽  
pp. 451-463
Author(s):  
R.W.C. (Bill) Arnott ◽  
Mike Tilston ◽  
Patricia Fraino ◽  
Lillian Navarro ◽  
Gerry Dumouchel ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Deep Sea ◽  
Size Fraction ◽  
Cross Flow ◽  
Fine Sand ◽  
Point Bar ◽  
Hydrostatic Pressure Gradient ◽  
Lateral Channel ◽  
High Resolution Images

ABSTRACT Channels with a sinuous planform are common in both continental and deep-marine environments on Earth, and similarly in high-resolution images of the surface of Mars. Whereas common in rivers, continuous lateral channel migration and point-bar deposition appear to be much less common in the deep sea. In the bends of rivers, near-bed flow driving point bar growth results from a cross-flow superelevation of the water surface that sets up a lateral hydrostatic pressure gradient driving an inward-directed flow near the bed. However, in deep-marine systems the surface between the turbidity current and overlying ambient fluid sits well above the channel margins, and therefore precludes a similar lateral superelevation of the current top. Here it is argued that the cross-flow component is related to a density gradient that mimics the effect of the hydrostatic pressure gradient in rivers, and develops as coarse suspended particles that experience little uplift, and therefore negligible overspill, become concentrated along the outer bank. This condition develops best in a two-part suspension made up of a highly concentrated, unstratified basal plug of coarse sediment overlain sharply by a dilute cloud of much finer sediment—a density structure that differs from the more typical upward exponential decrease in density. The abundance of coarse and fine sand, but depletion in the intermediate grain size fraction, is related to transgressive shelf processes and its influence on sediment supplied to the system, and in turn, the flow structure of the current. It is under these seemingly uncommon granulometric conditions that continuous laterally migrating channels, and accordingly, riverine-like point-bar deposition, is most common in the deep sea.

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