Osmotic stability of red cells in renal circulation requires rapid urea transport

1988 ◽  
Vol 254 (5) ◽  
pp. C669-C674 ◽  
Author(s):  
R. I. Macey ◽  
L. W. Yousef
Keyword(s):  
Lipid Bilayers ◽  
Physiological Role ◽  
Renal Medulla ◽  
Red Cells ◽  
Facilitated Diffusion ◽  
Urea Transport ◽  
Permeability Characteristics ◽  
Cortex Cell ◽  
Cell Stability ◽  
Michaelis Constants

Urea transport by the human erythrocyte occurs via an asymmetric-facilitated diffusion system with high Michaelis constants and high maximal velocities; the equivalent permeability in the limit of zero urea concentration is approximately 10(-3) cm/s (J. Gen. Physiol. 81: 221-237, 239-253, 1983). A physiological role for this system is revealed by numerical integration of the appropriate equations that show that rapid urea transport is essential for red cell stability in passing through the renal medulla. The calculation compares two cells. Cell A transports urea with permeability characteristics of normal red cells; cell B has urea permeability similar to lipid bilayers. On entering the hypertonic medulla, both cells shrink, but only B swells on leaving the medulla. The osmotic stress for cell B is greater than for A. Cell B is close to hypertonic hemolysis in the medulla and to hypotonic hemolysis in the cortex. Cell B remains swollen for some time after its exit; the resulting decreased deformability presents a hazard if B reenters the microcirculation. Furthermore, cell B removes a significant fraction of the filtered load of urea and compromises the osmotic gradients in the medulla.

Transport of water and urea in red blood cells

1984 ◽  
Vol 246 (3) ◽  
pp. C195-C203 ◽  
Author(s):  
R. I. Macey
Keyword(s):  
Red Blood Cells ◽  
Lipid Bilayers ◽  
Blood Cells ◽  
Renal Medulla ◽  
Water Channels ◽  
Facilitated Diffusion ◽  
Red Cell Membrane ◽  
Single File ◽  
Osmotic Stability ◽  
Water Transport Properties

Evidence for water channels in red blood cells is reviewed. In an entropically driven reaction, organic mercurials decrease water permeability, elevate the activation energy, and reduce the ratio of osmotic to diffusional water permeabilities to unity so that water transport properties of red blood cells are hardly distinguishable from lipid bilayers. It is concluded that mercurials close the water channels. A variety of kinetic, pharmacological, and comparative evidence converges on the conclusion that urea and other solutes are excluded from water channels. Urea apparently permeates the red cell membrane via a facilitated diffusion system, which plays an important role when red blood cells traverse the renal medulla; rapid urea transport helps preserve the osmotic stability and deformability of the cell, and it helps prevent dissipation of extracellular osmotic gradients. Water apparently traverses the channel via a single-file mechanism; the very low channel permeability of H+ is explained if the channel contains fixed charge, or alternatively, if the mobile water molecules within the channel do not form a continuum. An alternative unitary pore hypothesis for simultaneous transport of water, ions, and small solutes is also discussedl.

Urea transport in nephron segments from medullary rays of rabbits

1983 ◽  
Vol 244 (6) ◽  
pp. F622-F627 ◽  
Author(s):  
M. A. Knepper
Keyword(s):  
Renal Medulla ◽  
Significant Degree ◽  
Thick Ascending Limb ◽  
Urea Transport ◽  
Active Secretion ◽  
Apparent Permeability ◽  
Concentration Difference ◽  
Straight Tubules ◽  
Passive Absorption

To evaluate possible routes of urea delivery to the renal medulla, urea transport was studied in cortical thick ascending limbs and proximal straight tubules dissected from inner cortical medullary rays of rabbit kidneys. Urea was measured colorimetrically in the perfused, collected, and bath fluids. No evidence for active transport of urea was found in either segment. With imposed urea concentration differences between perfusion and bath fluids, there were significant passive fluxes of urea in both segments. The magnitude of the flux was independent of the direction of the concentration difference. Apparent permeability coefficients (X10(-5) cm/s) for urea were 2.0 for the cortical thick ascending limbs and 1.5 for the proximal straight tubules. Based on the measured permeability in the cortical thick ascending limb, substantial passive absorption of urea is predicted in vivo. This will contribute to the dilution of tubular fluid in this segment. The results in proximal straight tubules are compatible with passive urea secretion but not with a significant degree of active secretion.

Micropuncture study of urea transport in rat renal medulla

1966 ◽  
Vol 210 (5) ◽  
pp. 965-970 ◽  
Author(s):  
WE Lassiter ◽  
M Mylle ◽  
CW Gottschalk
Keyword(s):  
Renal Medulla ◽  
Urea Transport ◽  
Micropuncture Study

scholarly journals Luminal Mg2+, A Key Factor Controlling RYR2-mediated Ca2+ Release: Cytoplasmic and Luminal Regulation Modeled in a Tetrameric Channel

2008 ◽  
Vol 132 (4) ◽  
pp. 429-446 ◽  
Author(s):  
Derek R. Laver ◽  
Bonny N. Honen
Keyword(s):  
Cardiac Muscle ◽  
Lipid Bilayers ◽  
Calcium Release ◽  
Physiological Role ◽  
Competitive Effects ◽  
Channel Opening ◽  
Key Factor ◽  
Activation Mechanisms ◽  
Important Regulator ◽  
A Site

In cardiac muscle, intracellular Ca2+ and Mg2+ are potent regulators of calcium release from the sarcoplasmic reticulum (SR). It is well known that the free [Ca2+] in the SR ([Ca2+]L) stimulates the Ca2+ release channels (ryanodine receptor [RYR]2). However, little is known about the action of luminal Mg2+, which has not been regarded as an important regulator of Ca2+ release. The effects of luminal Ca2+ and Mg2+ on sheep RYR2 were measured in lipid bilayers. Cytoplasmic and luminal Ca2+ produced a synergistic increase in the opening rate of RYRs. A novel, high affinity inhibition of RYR2 by luminal Mg2+ was observed, pointing to an important physiological role for luminal Mg2+ in cardiac muscle. At diastolic [Ca2+]C, luminal Mg2+ inhibition was voltage independent, with Ki = 45 μM at luminal [Ca2+] ([Ca2+]L) = 100 μM. Luminal and cytoplasmic Mg2+ inhibition was alleviated by increasing [Ca2+]L or [Ca2+]C. Ca2+ and Mg2+ on opposite sides of the bilayer exhibited competitive effects on RYRs, indicating that they can compete via the pore for common sites. The data were accurately fitted by a model based on a tetrameric RYR structure with four Ca2+-sensing mechanisms on each subunit: activating luminal L-site (40-μM affinity for Mg2+ and Ca2+), cytoplasmic A-site (1.2 μM for Ca2+ and 60 μM for Mg2+), inactivating cytoplasmic I1-site (∼10 mM for Ca2+ and Mg2+), and I2-site (1.2 μM for Ca2+). Activation of three or more subunits will cause channel opening. Mg2+ inhibition occurs primarily by Mg2+ displacing Ca2+ from the L- and A-sites, and Mg2+ fails to open the channel. The model predicts that under physiological conditions, SR load–dependent Ca2+ release (1) is mainly determined by Ca2+ displacement of Mg2+ from the L-site as SR loading increases, and (2) depends on the properties of both luminal and cytoplasmic activation mechanisms.

Basolateral glucose transport in distal segments of the dog nephron

1991 ◽  
Vol 69 (7) ◽  
pp. 964-977 ◽  
Author(s):  
P. Vinay ◽  
J. Sénécal ◽  
J. Noël ◽  
C. Chirinian ◽  
M. C. Vinay ◽  
...  
Keyword(s):  
Glucose Transport ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Renal Medulla ◽  
Membrane Vesicles ◽  
Facilitated Diffusion ◽  
Thick Ascending Limb ◽  
Collecting Ducts ◽  
Sodium Dependent ◽  
Sodium Glucose Cotransport

The transport of glucose by canine thick ascending limbs (TAL) and inner medullary collecting ducts (IMCD) was studied using tubule suspensions and membrane vesicles. The uptake of D-[14C(U)]glucose by a suspension of intact TAL tubules was reduced largely by phloretin (Pt), moderately by phlorizin (Pz), and completely suppressed by a combination of both agents. A selective effect of Pz on the transport of [14C]α-methyl-D-glucoside, but not on 2-[3H]deoxyglucose, was also observed in TAL tubules. In contrast, glucose transport was unaffected by Pz but entirely suppressed by Pt alone in IMCD tubules. The metabolism of glucose was largely suppressed by Pt but unaffected by Pz in both types of tubules. Membrane vesicles were prepared from the red medulla and the white papilla or from TAL and IMCD tubules isolated from these tissues. Vesicle preparations from both tissues demonstrated a predominant carrier-mediated, sodium-independent, Pt- and cytochalasin B-sensitive glucose transport. Following purification of basolateral membrane on a Percoll gradient, the sodium-insensitive D-[14C(U)]glucose transport activity copurified with the activity of the basolateral marker Na+–K+ ATPase in both tissues. However, a small sodium-dependent and Pz-sensitive component of glucose transport was found in membrane vesicles prepared from the red medulla or from thick ascending limb tubules but not from the papilla nor collecting duct tubules. The kinetic analysis of the major sodium-independent processes showed that the affinity of the transporter for glucose was greater in collecting ducts (Km = 2.3 mM) than in thick ascending limbs (Km = 4.9 mM). We conclude that glucose gains access into the cells largely through a basolateral facilitated diffusion process in both segments. However a small sodium–glucose cotransport is also detected in membranes of TAL tubules. The transport of glucose presents an axial differentiation in the affinity of glucose transporters in the renal medulla, ensuring an adequate supply of glucose to the glycolytic inner medullary structures.Key words: basolateral membranes, tubules, medulla, thick ascending limbs, collecting ducts, glucose transport, phlorizin, phloretin, dog.

scholarly journals Role of PKC in the Regulation of the Human Kidney Chloride Channel ClC-Ka

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Andrea Gerbino ◽  
Roberta De Zio ◽  
Daniela Russo ◽  
Luigi Milella ◽  
Serena Milano ◽  
...  
Keyword(s):  
Physiological Role ◽  
Renal Medulla ◽  
Human Kidney ◽  
Inhibitory Effect ◽  
Hek293 Cells ◽  
Whole Cell Patch Clamp ◽  
New Information ◽  
Intracellular Ca ◽  
Accessory Subunit

Abstract The physiological role of the renal ClC-Ka/ClC-K1 channels is to confer a high Cl- permeability to the thin Ascending Limb of Henle (tAL), which in turn is essential for establishing the high osmolarity of the renal medulla that drives water reabsorption from collecting ducts. Here, we investigated by whole-cell patch-clamp measurements on HEK293 cells co-expressing ClC-Ka (tagged with GFP) and the accessory subunit barttin (tagged with m-Cherry) the effect of a natural diuretic extract from roots of Dandelion (DRE), and other compounds activating PKC, such as ATP, on ClC-Ka activity and its membrane localization. Treatment with 400 µg/ml DRE significantly inhibited Cl- currents time-dependently within several minutes. Of note, the same effect on Cl- currents was obtained upon treatment with 100 µM ATP. Pretreatment of cells with either the intracellular Ca2+ chelator BAPTA-AM (30 μM) or the PKC inhibitor Calphostin C (100 nM) reduced the inhibitory effect of DRE. Conversely, 1 µM of phorbol meristate acetate (PMA), a specific PKC activator, mimicked the inhibitory effect of DRE on ClC-Ka. Finally, we found that pretreatment with 30 µM Heclin, an E3 ubiquitin ligase inhibitor, did not revert DRE-induced Cl- current inhibition. In agreement with this, live-cell confocal analysis showed that DRE treatment did not induce ClC-Ka internalization. In conclusion, we demonstrate for the first time that the activity of ClC-Ka in renal cells could be significantly inhibited by the activation of PKC elicited by classical maneuvers, such as activation of purinergic receptors, or by exposure to herbal extracts that activates a PKC-dependent pathway. Overall, we provide both new information regarding the regulation of ClC-Ka and a proof-of-concept study for the use of DRE as new diuretic.

Large conducting potassium channel reconstituted from airway smooth muscle

1992 ◽  
Vol 262 (3) ◽  
pp. L327-L336 ◽  
Author(s):  
D. Savaria ◽  
C. Lanoue ◽  
A. Cadieux ◽  
E. Rousseau
Keyword(s):  
Smooth Muscle ◽  
Lipid Bilayers ◽  
Airway Smooth Muscle ◽  
Single Channel ◽  
Specific Inhibitor ◽  
Physiological Role ◽  
Membrane Receptors ◽  
K Channel ◽  
Open Probability ◽  
K Channels

Microsomal fractions were prepared from canine and bovine airway smooth muscle (ASM) by differential and gradient centrifugations. Surface membrane vesicles were characterized by binding assays and incorporated into planar lipid bilayers. Single-channel activities were recorded in symmetric or asymmetric K+ buffer systems and studied under voltage and Ca2+ clamp conditions. A large-conductance K(+)-selective channel (greater than 220 pS in 150 mM K+) displaying a high Ca2+, low Ba2+, and charybdotoxin (CTX) sensitivity was identified. Time analysis of single-channel recordings revealed a complex kinetic behavior compatible with the previous schemes proposed for Ca(2+)-activated K+ channels in a variety of biological surface membranes. We now report that the open probability of the channel at low Ca2+ concentration is enhanced on in vitro phosphorylation, which is mediated via an adenosine 3',5'-cyclic monophosphate-dependent protein kinase. In addition to this characterization at the molecular level, a second series of pharmacological experiments were designed to assess the putative role of this channel in ASM strips. Our results show that 50 nM CTX, a specific inhibitor of the large conducting Ca(2+)-dependent K+ channel, prevents norepinephrine transient relaxation on carbamylcholine-precontracted ASM strips. It was also shown that CTX reversed the steady-state relaxation induced by vasoactive intestinal peptide and partially antagonized further relaxation induced by cumulative doses of this potent bronchodilatator. Thus it is proposed that the Ca(2+)-activated K+ channels have a physiological role because they are indirectly activated on stimulation of various membrane receptors via intracellular mechanisms.

Cyclopropane ring formation in membrane lipids of bacteria

1997 ◽  
Vol 61 (4) ◽  
pp. 429-441 ◽  
Author(s):  
D W Grogan ◽  
J E Cronan
Keyword(s):  
Fatty Acids ◽  
Double Bond ◽  
Lipid Bilayers ◽  
Unsaturated Fatty Acids ◽  
Membrane Lipids ◽  
Cyclopropane Ring ◽  
Saturated Fatty Acids ◽  
Physiological Role ◽  
Phospholipid Bilayer ◽  
Valuable Insight

It has been known for several decades that cyclopropane fatty acids (CFAs) occur in the phospholipids of many species of bacteria. CFAs are formed by the addition of a methylene group, derived from the methyl group of S-adenosylmethionine, across the carbon-carbon double bond of unsaturated fatty acids (UFAs). The C1 transfer does not involve free fatty acids or intermediates of phospholipid biosynthesis but, rather, mature phospholipid molecules already incorporated into membrane bilayers. Furthermore, CFAs are typically produced at the onset of the stationary phase in bacterial cultures. CFA formation can thus be considered a conditional, postsynthetic modification of bacterial membrane lipid bilayers. This modification is noteworthy in several respects. It is catalyzed by a soluble enzyme, although one of the substrates, the UFA double bond, is normally sequestered deep within the hydrophobic interior of the phospholipid bilayer. The enzyme, CFA synthase, discriminates between phospholipid vesicles containing only saturated fatty acids and those containing UFAs; it exhibits no affinity for vesicles of the former composition. These and other properties imply that topologically novel protein-lipid interactions occur in the biosynthesis of CFAs. The timing and extent of the UFA-to-CFA conversion in batch cultures and the widespread distribution of CFA synthesis among bacteria would seem to suggest an important physiological role for this phenomenon, yet its rationale remains unclear despite experimental tests of a variety of hypotheses. Manipulation of the CFA synthase of Escherichia coli by genetic methods has nevertheless provided valuable insight into the physiology of CFA formation. It has identified the CFA synthase gene as one of several rpoS-regulated genes of E. coli and has provided for the construction of strains in which proposed cellular functions of CFAs can be properly evaluated. Cloning and manipulation of the CFA synthase structural gene have also enabled this novel but extremely unstable enzyme to be purified and analyzed in molecular terms and have led to the identification of mechanistically related enzymes in clinically important bacterial pathogens.

H2O2 and ethanol act synergistically to gate ryanodine receptor/calcium-release channel

2000 ◽  
Vol 279 (5) ◽  
pp. C1366-C1374 ◽  
Author(s):  
Toshiharu Oba ◽  
Tatsuya Ishikawa ◽  
Takashi Murayama ◽  
Yasuo Ogawa ◽  
Mamoru Yamaguchi
Keyword(s):  
Skeletal Muscle ◽  
Lipid Bilayers ◽  
Ryanodine Receptor ◽  
Calcium Release ◽  
Physiological Role ◽  
Channel Activity ◽  
Calcium Release Channel ◽  
Open Probability ◽  
Skeletal Muscle Function ◽  
Release Channel

We examined the effect of low concentrations of H2O2 on the Ca2+-release channel/ryanodine receptor (RyR) to determine if H2O2 plays a physiological role in skeletal muscle function. Sarcoplasmic reticulum vesicles from frog skeletal muscle and type 1 RyRs (RyR1) purified from rabbit skeletal muscle were incorporated into lipid bilayers. Channel activity of the frog RyR was not affected by application of 4.4 mM (0.02%) ethanol. Open probability ( P o) of such ethanol-treated RyR channels was markedly increased on subsequent addition of 10 μM H2O2. Increase of H2O2to 100 μM caused a further increase in channel activity. Application of 4.4 mM ethanol to 10 μM H2O2-treated RyRs activated channel activity. Exposure to 10 or 100 μM H2O2 alone, however, failed to increase P o. Synergistic action of ethanol and H2O2 was also observed on the purified RyR1 channel, which was free from FK506 binding protein (FKBP12). H2O2 at 100–500 μM had no effect on purified channel activity. Application of FKBP12 to the purified RyR1 drastically decreased channel activity but did not alter the effects of ethanol and H2O2. These results suggest that H2O2 may play a pathophysiological, but probably not a physiological, role by directly acting on skeletal muscle RyRs in the presence of ethanol.

The membrane permeability of nonelectrolytes and carbohydrate metabolism of Amazon fish red cells

1978 ◽  
Vol 56 (4) ◽  
pp. 863-869 ◽  
Author(s):  
Hyun Dju Kim ◽  
R. E. Isaacks
Keyword(s):  
Membrane Permeability ◽  
Carbohydrate Metabolism ◽  
Diffusion Mechanism ◽  
Red Cells ◽  
Facilitated Diffusion ◽  
Metabolic Substrates ◽  
Urea Permeability ◽  
Arapaima Gigas ◽  
Electric Eel ◽  
Order Of Magnitude

The membrane permeability to nonelectrolytes and carbohydrate metabolism were examined in red cells obtained from the Amazon fishes including the electric eel (Electrophorus electrocus), the arawana (Osteoglossum bicirrhosum), the pirarucu (Arapaima gigas), the lungfish (Lepidosireti paradoxa), and the armored catfish (Pterygoplichthys). Glucose permeability was fastest in the electric eel, followed by the lungfish. The red cells of the arawana were only slightly permeable to glucose. Both the armored catfish and the pirarucu red cells were found to be totally impermeable to glucose. There was no evidence for the presence of the facilitated diffusion mechanism for glucose transport in any of these fish red cells. In sharp contrast with glucose, red cells of all five species were quite permeable to ribose and urea. Urea permeability of red cells decreased in order of magnitude with the lungfish > the electric eel > the arawana > the armored catfish [Formula: see text] the pirarucu. The urea permeability of the lungfish was inhibited in the presence of phloretin.Of the two metabolic substrates, glucose but not ribose was metabolized to lactate with a concomitant contribution to ATP maintenance by the lungfish red cells. Even though the glucose-impervious pirarucu cells could not utilize glucose, ribose was readily metabolized by the pirarucu cells.

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