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Multiphoton microscopy (MPM) offers a unique approach for addressing both the function and structure of an organ in near-real time in the live animal. The method however is limited by the tissue-specific penetration depth of the excitation laser. In the kidney, structures in the range of 100 µ from the surface are accessible for MPM. This limitation of MPM aggravates the investigation of the function of structures located deeper in the renal cortex, like the glomerulus and the juxtaglomerular apparatus. In view of the relevance of gene-targeted mice for investigating the function of these structures, we aimed to identify a mouse strain with a high percentage of superficially located glomeruli. The mean distance of the 30 most superficial glomeruli from the kidney surface was determined in 10 coµonly used mouse strains. The mean depth of glomeruli was 118.4±e.4, 123.0±2.7, 133.7±3.0, 132.3±2.6, 141.0±4.0, 145.3±4.3, 148.9±4.2, 151.6±2.7, 167.7±3.9, and 207.8±3.2 µ in kidney sections from 4-week-old C3H/HeN, BALB/cAnN, SJL/J, C57BL/6N, DBA/2N, CD1 (CRI), 129S2/SvPas, CB6F1, FVB/N and NMRI (Han) mice, respectively (n = 5 animals from each strain). The mean distance from the kidney surface of the most superficial glomeruli was significantly lower in the strains C3H/HeN Crl, BALB/cAnN, DBA/2NCrl, and C57BL/6N when compared to a peer group consisting of all the other strains (p,.0001). In 10-week-old mice, the most superficial glomeruli were located deeper in the cortex when compared to 4-week-old animals, with BALB/cAnN and C57BL/6N being the strains with the highest percentage of superficial glomeruli (25% percentile 116.7 and 121.9 µ, respectively). In suµary, due to significantly more superficial glomeruli compared to other coµonly used strains, BALB/cAnN and C57BL/ 6N mice appear to be particularly suitable for the investigation of glomerular function using MPM. [ABSTRACT FROM AUTHOR]

Based on the controversy about the relevance of cyclooxygenase-2 (Cox-2)-derived prostanoids from the macula densa for the control of the renin system, this study aimed to determine the interrelation between Cox-2 and renin expression in the mouse kidney. In control mice renin mRNA was readily detectable whilst renocortical Cox-2 mRNA abundance was at the detection limit of the RNase protection assay and no specific signals for Cox-2 were obtained by in situ hybridization or Western blot analysis. Experimental maneuvers such as low-salt diet, treatment with loop diuretics or angiotensin I converting enzyme inhibitors clearly increased renin mRNA abundance up to sevenfold, but under none of these conditions renocortical Cox-2 mRNA levels were significantly changed. Moreover, the strong stimulation of renin expression by angiotensin I-converting enzyme inhibition was not changed by the cyclooxygenase inhibitor ibuprofen, which in turn clearly lowered tissue prostanoid content. Our data suggest a marked divergence of renin and Cox-2 expression in the kidney cortex of C57Bl/6 mice with no clear evidence for a role of Cox-2-derived prostanoids from the macula densa in the regulation of renin expression. [ABSTRACT FROM AUTHOR]

In the past few years the pivotal role of kidney Cl-channels (ClC-K) channels in maintaining salt and water homeostasis in the kidney has been established. The aim of the present study was to investigate the influence of the loop diuretic furosemide on the gene expression of the kidney chloride channel ClC-K1 and its recently described functional subunit barttin. Male Sprague Dawley rats received the loop diuretic furosemide (12 mg/kg/day) for 6 days. Rats had free access to 0.9% NaCl, 0.1%KCl solution to prevent volume depletion. Localisation and regulation of ClC-K1 and barttin mRNA was analysed by RNase protection and in situ hybridisation. Nephron-specific regulation was investigated by microdissection and real-time PCR quantification. In furosemide-treated rats ClC-K1 mRNA decreased to half in the inner medulla. In the renal cortex and outer medulla ClC-K1 mRNA levels were weak and did not change. Under furosemide treatment barttin mRNA was regulated in parallel with ClC-K1 mRNA. A significant mRNA decrease occurred after furosemide treatment in inner medulla (0.50 fold), whereas cortical and outer medulla levels remained unaffected. 35S in situ hybridisation confirmed the regulation and distribution seen in the RNase protection assay experiments. Microdissection of the inner medullary collecting duct and thin limb of Henle's loop followed by real-time PCR revealed that CLC-K1 and barttin mRNA regulation in inner medulla was limited to the thin limb; mRNA levels in collecting ducts were not affected by furosemide treatment. Our findings imply that during furosemide treatment selective down-regulation of ClC-K1 and barttin mRNAs in thin limb plays a role in maintaining salt and water homeostasis. [ABSTRACT FROM AUTHOR]

The aim of the present study was to determine the molecular responses of the main salt-reabsorbing systems in the distal nephron to changes of salt load of the organism. For this purpose we analysed messenger ribonucleic acid (mRNA) levels for the bumetanide-sensitive Na+K+2Cl– cotransporter (BSC1), the thiazide-sensitive Na+Cl– cotransporter (TSC), the kidney-specific inwards rectifier K+ channel (ROMK), the amiloride-sensitive epithelial Na+ channel (ENaC) and the kidney-specific Cl– channel ClC-K2, in the cortex and inner and outer medulla of kidneys from male Sprague-Dawley rats fed a high- (8% w/w), normal- (0.6%) or low- (0.02%) salt diet or treated chronically with subcutaneous infusions of furosemide (12 mg/kg per day). BSC1 and ROMK mRNA levels did not differ between the four treatment groups. TSC mRNA increased during furosemide treatment 1.75-fold versus control but was not affected by a high- or a low-salt diet. The mRNA for the α-subunit of ENaC increased with the low-salt diet (about 1.5-fold) and with furosemide (about 2.1-fold) in all kidney zones, but did not change with the high-salt diet. Dietary salt loading down-regulated ClC-K2 mRNA in the outer medulla 0.6-fold versus control whilst furosemide treatment, but not the low-salt diet, increased ClC-K2 mRNA in the outer (1.6-fold) and inner medulla (2.0-fold). These findings suggest that gene expression of Na+ and Cl– entry pathways in the distal nephron are at least partly regulated by the salt load of the organism, such that salt-reabsorbing systems are stimulated by salt deficiency and suppressed by salt overload. [ABSTRACT FROM AUTHOR]

Erythropoietin (EPO) is the central hormone in the regulation of erythropoiesis. Synthesis of EPO and its constitutive release into the circulation are controlled by the transcriptional activity of the EPO gene. A key regulator of EPO is the dimeric hypoxia-inducible transcription factor (HIF), which has three isoforms. Paliege and co-workers provide convincing morphological evidence that it is the HIF-2 isoform that essentially triggers EPO in the kidney, which is the primary source of EPO in the body. [ABSTRACT FROM AUTHOR]