Cellular permeation pathways in a leaky epithelium: the human amniochorion

First published August 15, 2001; 10.1152/ajprenal.00021.2001.—The proximal nephron possesses a leaky epithelium with unique paracellular permeability properties that underlie its high rate of passive NaCl and water reabsorption, but the molecular basis is unknown. The claudins are a large family of transmembrane proteins that are part of the tight junction complex and likely form structural components of a paracellular pore. To localize claudin-2 in the mouse kidney, we performed in situ hybridization using an isoform-specific riboprobe and immunohistochemistry using a polyclonal antibody directed against a COOH-terminal peptide. Claudin-2 mRNA and protein were found throughout the proximal tubule and in the contiguous early segment of the thin descending limb of long-looped nephrons. The level of expression demonstrated an axial increase from proximal to distal segments. In confocal images, the subcellular localization of claudin-2 protein coincided with that of the tight junction protein ZO-1. Our findings suggest that claudin-2 is a component of the paracellular pathway of the most proximal segments of the nephron and that it may be responsible for their uniquely leaky permeability properties.

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Ion transport in goby intestine: cellular mechanism of urotensin II stimulation

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1985.249.2.g284 ◽

1985 ◽

Vol 249 (2) ◽

pp. G284-G293

Author(s):

C. A. Loretz ◽

M. E. Howard ◽

A. J. Siegel

Keyword(s):

Apical Membrane ◽

Apical Cell ◽

Phosphodiesterase Inhibitor ◽

Membrane Conductance ◽

Urotensin Ii ◽

Apical Cell Membrane ◽

Absorptive Cells ◽

Ion Substitution ◽

Columnar Cells ◽

Leaky Epithelium

The Na- and Cl-absorbing goby posterior intestinal epithelium is composed predominantly of mitochondria-rich, tall columnar cells. Glass intracellular microelectrode recording technique was applied to absorptive cells of this relatively leaky epithelium to measure apical cell membrane potential difference (psi mc) and apical membrane fractional resistance. As determined by ion-substitution studies, absorptive cells are characterized by a large, Ba2+-inhibitable apical K conductance, which is a major factor determining psi mc and smaller Cl and Na conductances. Inhibition of the apical Na-Cl-coupled influx directly by furosemide or indirectly by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine produced hyperpolarization of psi mc, consistent with the greater apical membrane conductance to Cl than Na. The urophysial neurosecretory peptide urotensin II, which stimulates Na-Cl-coupled absorption, markedly depolarized psi mc in posterior intestinal tissues from 5% seawater-adapted gobies. This response is consistent with a stimulatory effect of urotensin II at the apical membrane carrier rather than at the basolateral Na-K-ATPase. Urotensin II is without effect on psi mc in tissues from seawater-adapted fish and somatostatin, a natural analogue of urotensin II, is without effect on tissues from fish adapted to either salinity. This specificity parallels that determined using radiotracer fluxes.

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Fluid Absorption in the Kidney Proximal Tubule

Physiology ◽

10.1152/physiologyonline.1987.2.1.22 ◽

1987 ◽

Vol 2 (1) ◽

pp. 22-26

Author(s):

JA Schafer

Keyword(s):

Proximal Tubule ◽

Water Flow ◽

Water Permeability ◽

Interstitial Fluid ◽

High Water ◽

Fluid Absorption ◽

Humoral Factors ◽

Solute Absorption ◽

Leaky Epithelium

Fluid absorption in the proximal tubule can be driven by a small osmotic difference between the luminal and interstitial fluids because this leaky epithelium has a high water permeability. The osmotic difference is produced by solute absorption, which tends to dilute the luminal fluid and concentrate the interstitial fluid. However, important questions remain unanswered regarding the pathway for water flow and the role of hemodynamic and humoral factors.

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Na+-K+-ATPase and Na+/Ca2+exchange activities in gills of hyperregulatingCarcinus maenas

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1999.276.2.r490 ◽

1999 ◽

Vol 276 (2) ◽

pp. R490-R499 ◽

Cited By ~ 12

Author(s):

Čedomil Lucu ◽

Gert Flik

Keyword(s):

Atpase Activity ◽

Specific Activity ◽

Short Circuit ◽

Carcinus Maenas ◽

High Capacity ◽

Short Circuit Current ◽

Total Activity ◽

Camp Content ◽

Dependent Protein ◽

Leaky Epithelium

Na+-K+-ATPase and Na+/Ca2+exchange activities were studied in gills of Carcinus maenas in seawater (SW) and after transfer to dilute seawater (DSW). Carcinushyperregulates its hemolymph osmolarity through active uptake of Na+, Cl−, and Ca2+. In DSW total Na+-K+-ATPase activity in posterior gills quadrupled; Na+/Ca2+exchange specific activity was unaffected, and total activity increased 1.67-fold. Short-circuit current ( Isc) in voltage-clamped posterior gill hemilamellae was −181 μA/cm2in SW and −290 μA/cm2in DSW and up to 90% ouabain sensitive; conductivity was similar in SW or DSW (42 and 46 mS/cm2, respectively) and representative of a leaky epithelium. The new steady state of hemolymph osmolarity 24 h after DSW transfer was preceded, already 3 h after transfer, by increased Na+-K+-ATPase but not Na+/Ca2+exchange activity. Western blot analysis indicated that the amount of Na+-K+-ATPase protein had increased 2.1-fold in crabs acclimated 3 wk to DSW; however, 4 h after DSW transfer no difference in the amount of Na+-K+-ATPase protein was observed. After DSW transfer branchial cAMP content decreased. A negative correlation between branchial Na+-K+-ATPase activity and cAMP content points to rapid regulation of Na+-K+-ATPase through cAMP-dependent protein kinase A activity. Ca2+transport may depend on the high-capacity Na+/Ca2+exchanger coupled to the versatile sodium pump.

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Endocytosis of Polypeptides in Rabbit Nasal Respiratory Mucosa

Physiology ◽

10.1152/physiologyonline.1997.12.5.219 ◽

1997 ◽

Vol 12 (5) ◽

pp. 219-225 ◽

Cited By ~ 2

Author(s):

D Cremaschi ◽

C Porta ◽

R Ghirardelli

Keyword(s):

Vesicle Fusion ◽

Metabolic Inhibitors ◽

Receptor Recycling ◽

Respiratory Mucosa ◽

Saturation Kinetics ◽

Leaky Epithelium

The nasal respiratory mucosa of the rabbit has a leaky epithelium actively transporting polypeptides by a specific transcytosis probably involved in sampling antigens. The transfer displays saturation kinetics and is abolished by metabolic inhibitors, actin filamet and microtubule disassemblers, inhibitors of vesicle fusion, and receptor recycling;it accepts polypeptide-covered but not uncovered nanoparticles.

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Failure of 2,4,6-triaminopyrimidine (TAP) to block sodium pathways in a ?leaky? epithelium

Pflügers Archiv - European Journal of Physiology ◽

10.1007/bf00581433 ◽

1979 ◽

Vol 379 (3) ◽

pp. 287-290 ◽

Cited By ~ 2

Author(s):

B. Fossat ◽

B. Lahlou

Keyword(s):

Leaky Epithelium

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Transmembrane and transepithelial movement of calcium during stimulus-secretion coupling

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1981.241.2.g150 ◽

1981 ◽

Vol 241 (2) ◽

pp. G150-G158 ◽

Cited By ~ 1

Author(s):

J. O'Doherty ◽

R. J. Stark

Keyword(s):

Salivary Secretion ◽

Phormia Regina ◽

Transepithelial Transport ◽

Enzyme Release ◽

Bathing Medium ◽

Stimulus Concentration ◽

Electrophysiological Studies ◽

Stimulus Secretion Coupling ◽

Paracellular Shunt ◽

Leaky Epithelium

Electrophysiological studies were undertaken to determine the transmembrane and transepithelial changes in free Ca2+ concentration that occur during serotonin-induced secretion in the salivary glands of the blowfly, Phormia regina. Ca-selective and conventional microelectrodes were used to measure intracellular and luminal Ca2+ concentrations ([Ca]L), serosal membrane and transepithelial potentials (Em, Etr), and their changes during serotonin (5-hydroxytryptamine, 5HT)-induced salivary secretion. The effect of stimulus concentration on these parameters and enzyme release was also determined. Previous studies provided evidence that serosal stimulation with 10(-8) M 5HT caused a hyperpolarization of Em and short phasic two- to threefold increases in [Ca]i. In these studies, higher concentrations of 5HT (10(-7) M) resulted in depolarization of Em by 13 +/- 1.2 mV and of ECa by 64 +/- 2.1 mV, a dramatic increase in [Ca]i, and a decrease in enzyme release. In addition, serotonin (10(-8) M) reduced the normal spontaneous Etr (+19.6 +/- 1 mV) to near zero while causing an increase in [Ca]L from 1.3 +/- 0.3 X 10(-5) mM to 2.0 +/- 0.1 X 10(-3) mM, a concentration isomolar with that of the bathing medium. These results provide direct electrochemical evidence that, during stimulus-secretion coupling of the salivary epithelial cells, the neurohormone serotonin controls the secretory response by the regulation of intracellular Ca2+ and induces transepithelial transport of Ca2+, thereby suggesting that, during secretion, the neurohormone causes the salivary gland to behave as a "leaky epithelium" by activating the paracellular shunt pathways.

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