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PubMedDate not supplied

Increased Ca++ or mg++ concentration reduces relative tight-junction permeability to Na+ in the cortical thick ascending limb of Henle's loop of rabbit kidney.

We have tested whether increased Ca++ and Mg++ concentrations have an effect on transepithelial voltage (PDte) and transepithelial resistance (Rte) in isolated perfused cortical thick ascending limbs (cTAL) of rabbit kidney. The divalent cations added at 2.5, 5.0 and 10.0 mmol.l-1 to the lumen or peritubular bath perfusate led to a concentration-dependent increase in Rte. The maximal response in Rte was observed between 5 and 10 mmol.l-1. No significant change in active transepithelial potential difference (PDte) was observed. The increase in Rte still occurred when the transcellular current was reduced by Ba++ (3 mmol.l-1) added to the lumen perfusate. This suggests that the increase in Rte caused by Ca++ and Mg++ is due to a modification of the paracellular shunt pathway. In the absence of active transport, i.e. when furosemide (5.10(-5) mol.l-1) was added to the lumen perfusate. Ca++ and Mg++ reduced the transepithelial diffusion potential generated by a NaCl gradient established across the epithelium, and thus produced a reduction of the relative permeability for Na+ over Cl- (PNa+/PCl-) of the paracellular shunt pathway. This indicates that divalent cations increase Rte by reducing the sodium permeability of the tight junctions. The observed Ca++ and Mg++ induced reduction of the sodium permeability of the paracellular pathway corresponds to a decrease in net Na+ reabsorption by 5-10%. Since it has been demonstrated that peptide hormones such as parathyrin (PTH) modulate divalent cation and NaCl reabsorptions, in a second series of experiments we tested the effects of PTH (2-20 USP.l-1) and dbcAMP (10(-3) mol.l-1) on PDte and Rte of isolated perfused cTAL segments of rabbit nephron. Neither Rte nor PDte were affected by PTH or dbcAMP.

Animals↗
PubMed1993

Cellular heterogeneity of ammonium ion transport across the basolateral membrane of the hamster medullary thick ascending limb of Henle's loop.

The epithelia of the medullary thick ascending limb (MAL) consists of two cell types, high (HBC) and low basolateral conductance (LBC) cell, depending on the K+ conductance of the basolateral membrane. The NH4+ conductance distinct from the K+ conductance has been suggested to exist in the proximal tubule, MAL cell, and Xenopus oocyte. The present study was designed to examine whether there is a conductive NH4+ transport system distinct from K+ conductance in two different cell types of the hamster MAL perfused in vitro. The basolateral membrane voltage (VB) was measured by impaling cells with conventional microelectrodes. Addition of NH4+ to the bath depolarized VB in a dose-dependent manner in both cell types. The response was maintained in the absence of HCO3-. When the VB deflection elicited upon 50 mM KCl or NH4Cl in the bath (delta VBK+ or delta VBNH4+) were compared, delta VBNH4+ was almost the same as delta VBK+ in the HBC cell, whereas the former was greater than the latter in the LBC. In the HBC cell, 10 mM Ba2+ in the bath equally suppressed both delta VBK+ and delta VBNH4+, whereas in the LBC cell it suppressed delta VBK+ with a small effect on delta VBNH4+, indicating that NH4+ is transported via a pathway distinct from Ba(2+)-sensitive K+ conductance. The VB deflection by NH4+ was unaffected by addition of 0.1 mM ouabain or 10 microM 5-nitro-2-(3-phenylpropylamino)-benzoate (a Cl- channel blocker) to the bath, excluding the contribution of the Na+, K+ pump or Cl- channel. An abrupt reduction of Na+ in the bath from 200 to 20 mM did not cause any changes in VB, suggesting that a nonselective cation channel may not account for the NH4+ transport. Amiloride at 10 microM inhibited delta VBNH4+ with a higher efficacy in the LBC cell. We conclude that a rheogenic NH4+ transport system independent from the K+ conductance exists in the basolateral membrane of the LBC cell of the hamster MAL, and may play some roles in the regulation of NH4+ transport.

Ammonia↗
PubMed1989

The histotopography and ultrastructure of the thin limb of the Henle's loop: a scanning electron microscopic study of the rat kidney.

The three-dimensional construction of the thin limb epithelium was demonstrated in all four segments previously determined by transmission electron microscopy. Special reference was given to the pattern and extent of both intercellular and intracellular interdigitation. In the thin limb of short-looped nephrons, epithelial cells were simple polygonal in shape. The cells showed fine intercellular and intracellular interdigitations of basolateral microprojections. The upper descending thin limb of long-looped nephrons was characterized by well-developed intercellular and intracellular interdigitations. Both types of interdigitations showed a double structure, as they were composed of primary lateral processes or deep basal grooves, with numerous secondary microprojections on their walls. This segment additionally revealed apical interdigitations of small laminar processes, which caused the fine undulation of luminal cell boundaries. In the lower descending thin limb of long-looped nephrons, the intercellular and intracellular interdigitations also showed the double structure, though diminished in degree. This segment lacked the fine apical interdigitations. The ascending thin limb was characterized by an elaborate pectineal pattern of intercellular interdigitations, and by the absence of intracellular interdigitations. The intercellular interdigitations in this segment were formed by thin primary processes oriented parallel to each other. No secondary microprojections were found on their lateral surfaces.

Animals↗
PubMed2001

Regulation of potassium channel Kir 1.1 (ROMK) abundance in the thick ascending limb of Henle's loop.

The renal outer medullary potassium channel (ROMK) of the thick ascending limb (TAL) is a critical component of the counter-current multiplication mechanism. In this study, two new antibodies raised to ROMK were used to investigate changes in the renal abundance of ROMK with treatments known to strongly promote TAL function. These antibodies specifically recognized protein of the predicted size of 45 kD in immunoblots of rat kidney or COS cells transfected with ROMK cDNA. Infusion of 1-deamino-(8-D-arginine)-vasopressin (dDAVP), a vasopressin V2 receptor-selective agonist, for 7 d into Brattleboro rats resulted in dramatic increases in apical membrane labeling of ROMK in the TAL of dDAVP-treated rats, as assessed by immunocytochemical analyses. Using immunoblotting, a more than threefold increase in immunoreactive ROMK levels was observed in the outer medulla after dDAVP infusion. Restriction of water intake to increase vasopressin levels also significantly increased TAL ROMK immunolabeling and abundance in immunoblots. In addition, dietary Na(+) levels were varied to determine whether ROMK abundance was also affected under other conditions known to alter TAL transport. Rats fed higher levels of sodium, as either NaCl or NaHCO(3) (8 mEq/250 g body wt per d), exhibited significantly increased density of the 45-kD band, compared with the respective control animals. Moreover, in rats fed a low-NaCl diet (0.25 mEq/250 g body wt per d), a 50% decrease in band density for the 45-kD band was observed (relative to control rats fed 2.75 mEq/250 g body wt per d of NaCl). These results demonstrate that long-term adaptive changes in ROMK abundance occur in the TAL with stimuli that enhance transport by this segment.

Animals↗
PubMed1988

Is there any tubular secretion of protein?

Immunohistological investigations performed with the PAP method on tubular casts in the thick Henle loops and in the distal convoluted tubules led to the following results. 1) In control kidneys, casts consisting of sIgA and IgM occur, mostly isolated, in 30% and 20%, respectively, of cases. On the other hand IgG casts, likewise isolated, are only observed in 7% of cases. 2) In the case of mesangioproliferative glomerulonephritis of the IgA and non-IgA nephritis type, casts consisting of sIgA and IgM are observed more often than in control kidneys, especially when the serum creatinine concentration exceeds 1.3 mg%; i.e., the glomerular filtration is reduced. 3) In kidneys with inflammatory and non-inflammatory glomerular diseases which had led to nephrotic syndrome, casts consisting of sIgA and IgM are not observed more often than in kidneys with glomerulonephritides which had not been accompanied by nephrotic syndrome. 4) In kidneys with severe impairment of the excretory function (rapidly-progressive glomerulonephritis, primary malignant nephrosclerosis, acute renal failure) casts consisting of sIgA and IgM are observed more often than in controls but not more often than in IgA and non-IgA nephritides with increased serum creatinine concentration. 5) In kidneys which had become aglomerular as a result of scarring of the glomeruli, with atrophic proximal tubules and preserved epithelia of the ascending loop of Henle, casts consisting of sIgA and IgM as well as secretory component occur in a large quantity.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗