Renal micropuncture studies have greatly changed our views on the pathophysiology of acute renal failure caused by nephrotoxins. Formerly, this type of renal insufficiency was attributed to a direct effect of the nephrotoxins on tubule epithelial permeability. According to that theory, glomerular filtration was not greatly diminished, the filtrate formed being absorbed almost quantitatively and nonselectively across damaged tubule epithelium. Studies in a wide variety of rat models have now shown glomerular filtration to be reduced to a level which will inevitably cause renal failure in and of itself. Passive backflow of filtrate across tubular epithelium is either of minor degree or nonexistent even in models where frank tubular necrosis has occurred. This failure of filtration cannot be attributed to tubular obstruction since proximal tubule pressure is distinctly subnormal in most models studied. Instead, filtration failure appears best attributed to intrarenal hemodynamic alterations. While certain facts tend to incriminate the renin-angiotensin system as the cause of the hemodynamic aberrations, others argue to the contrary. The issue is underactive investigation. (+info)
(2/939) Renal function tests: what do they mean? A review of renal anatomy, biochemistry, and physiology.
Renal physiology, biochemistry, and anatomy are reviewed. For the most part, those aspects of these disciplines will be discussed which relate directly to the question of the evaluation of nephrotoxicity. In addition, emphasis is placed on those procedures and techniques which are useful in the evaluation of nephrotoxicity. A detailed discussion of histological and anatomical considerations is not given, since this is probably the least useful criterion for evaluation of renal damage. This information is intended as background for the remainder of the symposium which will be directed toward an understanding of specific nephrotoxicity phenomena. (+info)
(3/939) Sodium reabsorption and distribution of Na+/K+-ATPase during postischemic injury to the renal allograft.
BACKGROUND: A loss of proximal tubule cell polarity is thought to activate tubuloglomerular feedback, thereby contributing to glomerular filtration rate depression in postischemic acute renal failure (ARF). METHODS: We used immunomicroscopy to evaluate the segmental distribution of Na+/K+-ATPase in tubules of recipients of cadaveric renal allografts. Fractional excretion (FE) of sodium and lithium was determined simultaneously. Observations were made on two occasions: one to three hours after graft reperfusion (day 0) and again on post-transplant day 7. An inulin clearance below or above 25 ml/min on day 7 was used to divide subjects into groups with sustained (N = 15) or recovering (N = 16) ARF, respectively. RESULTS: In sustained ARF, the fractional excretion of sodium (FENa) was 40 +/- 6% and 11 +/- 5%, and the fractional excretion of lithium (FELi) was 76 +/- 5% and 70 +/- 2% on days 0 and 7, respectively. Corresponding findings in recovering ARF were 28 +/- 2% and 6 +/- 2% for the FENa and 77 +/- 4% and 55 +/- 3% (P < 0.05 vs. sustained) for FELi. Na+/K+-ATPase distribution in both groups was mainly basolateral in distal straight and convoluted tubule segments and collecting ducts. However, Na+/K+-ATPase was poorly retained in the basolateral membrane of proximal convoluted and straight tubule segments in sustained and recovering ARF on both days 0 and 7. CONCLUSIONS: We conclude that loss of proximal tubule cell polarity for Na+/K+-ATPase distribution is associated with enhanced delivery of filtered Na+ to the macula densa for seven days after allograft reperfusion. Whether an ensuing activation of tubuloglomerular feedback is an important cause of glomerular filtration rate depression in this form of ARF remains to be determined. (+info)
(4/939) Adenosine inhibits the transfected Na+-H+ exchanger NHE3 in Xenopus laevis renal epithelial cells (A6/C1).
1. Adenosine influences the vectorial transport of Na+ and HCO3- across kidney epithelial cells. However, its action on effector proteins, such as the Na+-H+ exchanger NHE3, an epithelial brush border isoform of the Na+-H+ exchanger (NHE) gene family, is not yet defined. 2. The present study was conducted in Xenopus laevis distal nephron A6 epithelia which express both an apical adenosine receptor of the A1 type (coupled to protein kinase C (PKC)) and a basolateral receptor of the A2 type (coupled to protein kinase A (PKA)). The untransfected A6 cell line expresses a single NHE type (XNHE) which is restricted to the basolateral membrane and which is activated by PKA. 3. A6 cell lines were generated which express exogenous rat NHE3. Measurements of side-specific pHi recovery from acid loads in the presence of HOE694 (an inhibitor with differential potency towards individual NHE isoforms) detected an apical resistant Na+-H+ exchange only in transfected cell lines. The sensitivity of the basolateral NHE to HOE694 was unchanged, suggesting that exogenous NHE3 was restricted to the apical membrane. 4. Stimulation of the apical A1 receptor with N 6-cyclopentyladenosine (CPA) inhibited both apical NHE3 and basolateral XNHE. These effects were mimicked by the addition of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and partially prevented by the PKC inhibitor calphostin C which also blocked the effect of PMA. 5. Stimulation of the basolateral A2 receptor with CPA inhibited apical NHE3 and stimulated basolateral XNHE. These effects were mimicked by 8-bromo-cAMP and partially prevented by the PKA inhibitor H89 which entirely blocked the effect of 8-bromo-cAMP. 6. In conclusion, CPA inhibits rat NHE3 expressed apically in A6 epithelia via both the apical PKC-coupled A1 and the basolateral PKA-coupled A2 adenosine receptors. (+info)
(5/939) Second messenger production in avian medullary nephron segments in response to peptide hormones.
We examined the sites of peptide hormone activation within medullary nephron segments of the house sparrow (Passer domesticus) kidney by measuring rates of hormone-induced generation of cyclic nucleotide second messenger. Thin descending limbs, thick ascending limbs, and collecting ducts had baseline activity of adenylyl cyclase that resulted in cAMP accumulation of 207 +/- 56, 147 +/- 31, and 151 +/- 41 fmol. mm-1. 30 min-1, respectively. In all segments, this activity increased 10- to 20-fold in response to forskolin. Activity of adenylyl cyclase in the thin descending limb was stimulated approximately twofold by parathyroid hormone (PTH) but not by any of the other hormones tested [arginine vasotocin (AVT), glucagon, atrial natriuretic peptide (ANP), or isoproterenol, each at 10(-6) M]. Thick ascending limb was stimulated two- to threefold by both AVT and PTH; however, glucagon and isoproterenol had no effect, and ANP stimulated neither cAMP nor cGMP accumulation. Adenylyl cyclase activity in the collecting duct was stimulated fourfold by AVT but not by the other hormones; likewise, ANP did not stimulate cGMP accumulation in this segment. These data support a tubular action of AVT and PTH in the avian renal medulla. (+info)
(6/939) Developmental expression of sodium entry pathways in rat nephron.
During the past several years, sites of expression of ion transport proteins in tubules from adult kidneys have been described and correlated with functional properties. Less information is available concerning sites of expression during tubule morphogenesis, although such expression patterns may be crucial to renal development. In the current studies, patterns of renal axial differentiation were defined by mapping the expression of sodium transport pathways during nephrogenesis in the rat. Combined in situ hybridization and immunohistochemistry were used to localize the Na-Pi cotransporter type 2 (NaPi2), the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2), the thiazide-sensitive Na-Cl cotransporter (NCC), the Na/Ca exchanger (NaCa), the epithelial sodium channel (rENaC), and 11beta-hydroxysteroid dehydrogenase (11HSD). The onset of expression of these proteins began in post-S-shape stages. NKCC2 was initially expressed at the macula densa region and later extended into the nascent ascending limb of the loop of Henle (TAL), whereas differentiation of the proximal tubular part of the loop of Henle showed a comparatively retarded onset when probed for NaPi2. The NCC was initially found at the distal end of the nascent distal convoluted tubule (DCT) and later extended toward the junction with the TAL. After a period of changing proportions, subsegmentation of the DCT into a proximal part expressing NCC alone and a distal part expressing NCC together with NaCa was evident. Strong coexpression of rENaC and 11HSD was observed in early nascent connecting tubule (CNT) and collecting ducts and later also in the distal portion of the DCT. Ontogeny of the expression of NCC, NaCa, 11HSD, and rENaC in the late distal convolutions indicates a heterogenous origin of the CNT. These data present a detailed analysis of the relations between the anatomic differentiation of the developing renal tubule and the expression of tubular transport proteins. (+info)
(7/939) A novel p64-related Cl- channel: subcellular distribution and nephron segment-specific expression.
Several closely related proteins that have been implicated as chloride channels of intracellular membranes have recently been described. We report here the molecular cloning and characterization of a new member of this family from human cells. On the basis of sequence similarity, we conclude that this new protein represents the human version of a previously described protein from rat brain named p64H1. The human version of p64H1 (huH1) is a 28.7-kDa protein that shows an apparent molecular mass of 31 kDa by SDS-PAGE. A single 4.5-kb message is detected on Northern blots and is present in all tissues probed. The protein is expressed in an intracellular vesicular pattern in Panc-1 cells that is distinct from the endoplasmic reticulum, fluid-phase endocytic, and transferrin-recycling compartments, but which does colocalize with caveolin. In human kidney, huH1 is highly expressed in a diffuse pattern in the apical domain of proximal tubule cells. huH1 is expressed less abundantly in a vesicular pattern in glomeruli and distal nephron. (+info)
(8/939) Intranephron distribution and regulation of endothelin-converting enzyme-1 in cyclosporin A-induced acute renal failure in rats.
Endothelin-1 (ET-1) is thought to play a significant role in acute renal failure induced by cyclosporin A (CsA). The cDNA sequence encoding endothelin-converting enzyme-1 (ECE-1), which produces the active form of ET-1 from big ET-1, was recently reported. To elicit the role of ECE-1 in the glomerular and tubular dysfunction induced by CsA, the effects of CsA on mRNA and protein expression of ECE-1 in rat kidney and on mRNA expression of prepro-ET-1 and ET A- and B-type receptors in glomeruli were studied. ECE-1 mRNA was detected in glomeruli and in whole nephron segments. ECE-1 mRNA expression was downregulated in all nephron segments at 24 h after CsA injection. Protein levels were also downregulated in glomeruli and in the outer and inner medulla. CsA rapidly increased prepro-ET-1 mRNA expression in glomeruli at 30 to 60 min after injection; this rapid increase was followed by an increase in plasma ET-1 levels. These increases were followed by decreased expression of ECE-1, ET A-type receptor, and ET B-type receptor mRNA at 6 h after injection, and serum creatinine levels were increased at 24 h after CsA injection. It is suggested that downregulation of glomerular and tubular ECE-1 expression may be caused by increased ET-1 synthesis in CsA-induced acute renal failure. (+info)