functional-assessment-intestinal-tight-junction-barrier-ion

Functional Assessment of Intestinal Tight Junction Barrier and Ion Permeability in Native Tissue by Ussing Chamber Technique

The Ussing chamber technique was first invented by the Danish scientist Hans Ussing in 1951 to study the transcellular transport of sodium across frog ...

University of Shizuoka

Many nutrients are absorbed via Na cotransport systems, and therefore it is predicted that nutrient absorption mechanisms require a large amount of luminal Na. It is thought that Na diffuses back into the lumen via paracellular pathways to support Na cotransport absorption. However, direct experimental evidence in support of this mechanism has not been shown. To elucidate this, we took advantage of claudin-15 deficient () mice, which have been shown to have decreased paracellular Na permeability. We measured glucose-induced currents (Δ) under open- and short-circuit conditions and simultaneously measured changes in unidirectional Na fluxes (Δ) in Ussing chambers. Under short-circuit conditions, application of glucose resulted in an increase in Δ and unidirectional mucosal to serosal Na (∆) flux in both wild-type and  mice. However, under open-circuit conditions, Δ was observed but ∆ was strongly inhibited in wild-type but not in  mice. In addition, in the duodenum of mice treated with cholera toxin, paracellular Na conductance was decreased and glucose-induced ∆ increment was observed under open-circuit conditions. We concluded that the Na which is absorbed by Na-dependent glucose cotransport is recycled back into the lumen via paracellular Na conductance through claudin-15, which is driven by Na cotransport induced luminal negativity.

Na-Coupled Nutrient Cotransport Induced Luminal Negative Potential and Claudin-15 Play an Important Role in Paracellular Na Recycling in Mouse Small Intestine.

Angulin-2/ILDR1 is a member of the angulin protein family, which is exclusively expressed at tricellular tight junctions in epithelia. Tricellular tight junctions are found where three cells meet and where three bicellular tight junction strands converge. Tricellular tight junctions are thought to be important for paracellular permeability of ions and water in epithelial tissues. It was recently reported that angulin-2/ILDR1 knockout mice have water transport abnormalities in the kidney. Since angulin-2/ILDR1 is the main tricellular tight junction protein in the large intestine, the goal of this research was to examine the effect of angulin-2/ILDR1 knockout on large intestinal paracellular water transport. We found that Ildr1 knockout mice showed no detectable phenotype other than deafness. In addition, paracellular transport as assessed by Ussing chamber was unchanged in Ildr1 knockout mice. However, we found that in the colon and the kidney of Ildr1 knockout mice, another tricellular tight junction protein, angulin-1/LSR, changes its expression pattern. We propose that with this replacement in tissue localization, angulin-1/LSR compensates for the loss of angulin-2/ILDR1 and maintains the barrier and function of the epithelia in the large intestine as well as the kidney.

Article	Year
Na-Coupled Nutrient Cotransport Induced Luminal Negative Potential and Claudin-15 Play an Important Role in Paracellular Na Recycling in Mouse Small Intestine. International journal of molecular sciences\| PubMed ID: 31936130	2020
Angulin-2/ILDR1, a tricellular tight junction protein, does not affect water transport in the mouse large intestine. Scientific reports\| PubMed ID: 32587380	2020

Wendy Hempstock

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