TY - JOUR
T1 - Transepithelial water and urea permeabilities of isolated perfused Munich-Wistar rat inner medullary thin limbs of Henle's loop
AU - Michele Nawata, C.
AU - Evans, Kristen K.
AU - Dantzler, William H.
AU - Pannabecker, Thomas L.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - To better understand the role that water and urea fluxes play in the urine concentrating mechanism, we determined transepithelial osmotic water permeability (Pf) and urea permeability (Purea) in isolated perfused Munich-Wistar rat long-loop descending thin limbs (DTLs) and ascending thin limbs (ATLs). Thin limbs were isolated either from 0.5 to 2.5 mm below the outer medulla (upper inner medulla) or from the terminal 2.5 mm of the inner medulla. Segment types were characterized on the basis of structural features and gene expression levels of the water channel aquaporin 1, which was high in the upper DTL (DTLupper), absent in the lower DTL (DTLlower), and absent in ATLs, and the Cl-1 channel ClCK1, which was absent in DTLs and high in ATLs. DTLupper Pf was high (3,204.5 ± 450.3 μm/s), whereas DTLlower showed very little or no osmotic Pf (207.8 ± 241.3 μm/s). Munich-Wistar rat ATLs have previously been shown to exhibit no Pf. DTLupper Purea was 40.0 ± 7.3 × 10-5 cm/s and much higher in DTLlower (203.8 ± 30.3 × 10-5 cm/s), upper ATL (203.8 ± 35.7 × 10-5 cm/s), and lower ATL (265.1 ± 49.8 × 10-5 cm/s). Phloretin (0.25 mM) did not reduce DTLupper Purea, suggesting that Purea is not due to urea transporter UT-A2, which is expressed in short-loop DTLs and short portions of some inner medullary DTLs close to the outer medulla. In summary, Purea is similar in all segments having no osmotic Pf but is significantly lower in DTLupper, a segment having high osmotic Pf. These data are inconsistent with the passive mechanism as originally proposed.
AB - To better understand the role that water and urea fluxes play in the urine concentrating mechanism, we determined transepithelial osmotic water permeability (Pf) and urea permeability (Purea) in isolated perfused Munich-Wistar rat long-loop descending thin limbs (DTLs) and ascending thin limbs (ATLs). Thin limbs were isolated either from 0.5 to 2.5 mm below the outer medulla (upper inner medulla) or from the terminal 2.5 mm of the inner medulla. Segment types were characterized on the basis of structural features and gene expression levels of the water channel aquaporin 1, which was high in the upper DTL (DTLupper), absent in the lower DTL (DTLlower), and absent in ATLs, and the Cl-1 channel ClCK1, which was absent in DTLs and high in ATLs. DTLupper Pf was high (3,204.5 ± 450.3 μm/s), whereas DTLlower showed very little or no osmotic Pf (207.8 ± 241.3 μm/s). Munich-Wistar rat ATLs have previously been shown to exhibit no Pf. DTLupper Purea was 40.0 ± 7.3 × 10-5 cm/s and much higher in DTLlower (203.8 ± 30.3 × 10-5 cm/s), upper ATL (203.8 ± 35.7 × 10-5 cm/s), and lower ATL (265.1 ± 49.8 × 10-5 cm/s). Phloretin (0.25 mM) did not reduce DTLupper Purea, suggesting that Purea is not due to urea transporter UT-A2, which is expressed in short-loop DTLs and short portions of some inner medullary DTLs close to the outer medulla. In summary, Purea is similar in all segments having no osmotic Pf but is significantly lower in DTLupper, a segment having high osmotic Pf. These data are inconsistent with the passive mechanism as originally proposed.
KW - Aquaporin
KW - Epithelial transport
KW - Renal medulla
KW - Urea transporter-A
KW - Urine concentrating mechanism
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U2 - 10.1152/ajprenal.00491.2013
DO - 10.1152/ajprenal.00491.2013
M3 - Article
SN - 1931-857X
VL - 306
SP - F123-F129
JO - American Journal of Physiology - Renal Physiology
JF - American Journal of Physiology - Renal Physiology
IS - 1
ER -