Cellular and Paracellular Transport Pathways

The kidney is the main organ regulating composition of body fluids. A considerable number of hormones control the activity of renal cells to maintain hydromineral equilibrium. It becomes more and more difficult to interpret this multihormonal control in terms of regulatory processes. To illustrate this complexity, the hormonal regulation of electrolyte transport in the nephron thick ascending limb is taken as an example. This nephron segment is largely responsible for two kidney functions: the urinary-concentrating ability (by its capacity to deliver hypertonic sodium chloride into the medullary interstitium) and regulation of magnesium excretion into final urine. Six hormones are presently identified as acting on the transport of both sodium chloride and magnesium ions in this nephron segment. Therefore, the pertinent question is how the thick ascending limb and, hence, the kidney, is capable of regulating water balance independently from magnesium balance. It is proposed that the hormones act in combination: circulating levels of the individual hormones acting on these cells may determine the configuration of the paracellular and transcellular transport pathways of the epithelium either in the “sodium” or “magnesium” mode. The configuration would depend on the distribution and activity of the receptor at the surface of the basolateral membrane in contact with the circulating hormones. This distribution along with stimulation of respective signal transduction pathways would lead to the final biological effects. It is already known that the distribution of cell receptors may vary according to factors such as age, nutritional variability, hormonal status, degree of desensitization of the receptors, etc. The modulation of hormonal responses would depend therefore on the degree of coupling of hormone-receptor complexes to different intracellular transduction pathways and on the resulting negative and/or positive interactions between these pathways.

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Claudin Tight Junction Proteins: Novel Aspects in Paracellular Transport

Peritoneal Dialysis International ◽

10.1177/089686080802800605 ◽

2008 ◽

Vol 28 (6) ◽

pp. 577-584 ◽

Cited By ~ 32

Author(s):

Constanze Will ◽

Michael Fromm ◽

Dominik Müller

Keyword(s):

Tight Junction ◽

Solute Transport ◽

Molecular Mechanisms ◽

Family Members ◽

Transport Processes ◽

Paracellular Transport ◽

Solute Flux ◽

Solute Fluxes ◽

Essential Components ◽

Renal Tubular

Claudins are essential components of the intercellular tight junction and major determinants of paracellular solute fluxes across epithelia and endothelia. Many members of this family display a distinct charge or size specificity, whereas others render the epithelium impermeable to transport. Due to intercellular localization, claudin-mediated transport processes are passive and driven by an electrochemical gradient. In epithelial tissues, claudins exhibit a temporal–spatial expression pattern corresponding with regional and local solute transport profiles. Whereas paracellular transport mechanisms in organs such as intestine and kidney have been extensively investigated, little is known about the molecular mechanisms determining solute transport in the peritoneum, and thus the determinants of peritoneal dialysis. Given the ubiquitous expression of claudins in endothelia and epithelia, it is predictable that claudins also contribute to pore formation and determination in the peritoneum, and that they are involved in solute flux. Therefore, we review the basic characteristics of claudin family members and their function as exemplified in renal tubular transport and give an outlook to what extent claudin family members might be of importance for solute reabsorption across the peritoneal membrane.

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Perfluoroalkyl acids on suspended particles: Significant transport pathways in surface runoff, surface waters, and subsurface soils

Journal of Hazardous Materials ◽

10.1016/j.jhazmat.2021.126159 ◽

2021 ◽

pp. 126159 ◽

Cited By ~ 1

Author(s):

Annesh Borthakur ◽

Meng Wang ◽

Meng He ◽

Katia Ascencio ◽

Jens Blotevogel ◽

...

Keyword(s):

Surface Waters ◽

Surface Runoff ◽

Suspended Particles ◽

Perfluoroalkyl Acids ◽

Transport Pathways

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A pressure induced reversal to the 9R perovskite in Ba3MoNbO8.5

Journal of Materials Chemistry A ◽

10.1039/d0ta11270d ◽

2021 ◽

Vol 9 (10) ◽

pp. 6567-6574

Author(s):

B. Sherwood ◽

C. J. Ridley ◽

C. L. Bull ◽

S. Fop ◽

J. M. S. Skakle ◽

...

Keyword(s):

Bulk Modulus ◽

Structural Transformation ◽

Pressure Response ◽

Energy Barriers ◽

Transport Pathways

The pressure response of Ba3MoNbO8.5 reveals a structural transformation, which acts to increase the energy barriers to migration along all available transport pathways, and an exceptionally low bulk modulus.

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