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Notes: 1. Cultured renomedullary interstitial cells (RMIC) isolated from 4-week-old Sprague-Dawley rat kidneys possess ETA receptors, as identified by reverse transcription–polymerase chain reaction (RT-PCR).2. Treatment with endothelin (ET)-1 (10−6 mol/L) increases the intracellular inositol 1,4,5-trisphosphate concentrations within 10 s and intracellular calcium concentrations after 7 s.3. Endothelin-1 (10−7 and 10−10 mol/L) induced increases in intracellular cAMP concentrations, but only in the presence of Nω-nitro-L-arginine, a nitric oxide synthase (NOS) inhibitor. Addition of ET-1 (10−10 mol/L) to the RMIC culture led to increases in intracellular cGMP concentrations through activation of NOS.4. In the presence of ET-1 (10−7 and 10−10 mol/L) and during NOS inhibition, RMIC responded with increased cell proliferation and extracellular matrix (ECM) synthesis. These responses were abolished by BQ-123 (10−6 mol/L), suggesting mediation via the ETA receptor subtype. The proliferative effect of ET-1 was also abolished by atrial natriuretic peptide (10−6 mol/L).5. The present study provides evidence that binding of ET-1 to ETA receptors on RMIC activates several intracellular second messenger systems that mediate cell proliferation and ECM synthesis.6. These results also highlight an important interaction between ET-1 and nitric oxide in the control of RMIC function.

Notes: 1. Using hybridization histochemistry renin gene expression has been localized in the juxtaglomerular apparatus (JGA) of the renal cortex in both mouse and sheep kidney.2. This technique also located renin gene expression in afferent arterioles and interlobular arteries distant from the glomerular tuft in lamb renal cortex.3. A short (30 mer) synthetic oligonucleotide probe, complementary to a region of the mouse submaxillary gland renin gene, specifically labelled mouse submaxillary gland and kidney.4. Hybridization histochemistry and Northern blot analysis using both the synthetic oligonucleotide (mouse) probe and a 700 base pair recombinant (sheep) probe showed differences in renin gene expression in the kidney in response to Na restriction in the mouse and Na depletion in the sheep.

Notes: Summary: Angirotensin II (AII) is a powerful humoral regulator of body fluid and electrolyte balance and arterial blood pressure. In the kidney, All influences renal haemodynamics and proximal tubular reabsorption of sodium through activation of All that mediate complex signal transduction pathways. Angiotensin II is also implicated in the pathophysiological process of some progressive renal diseases. Pharmacological characterization and molecular cloning of All receptor reveals at least two major subtypes of All receptors, AT1 and AT2, in the kidney and other tissues. the AT1 receptor cDNA encodes a 359 amino acid protein with structure typical of seven transmembrane G-protein coupled receptors. Two isoforms of AT1 receptor, AT1A and AT1B, are known in rodents, but probably only one occurs in other mammals including humans. the AT2 receptor cDNA, a 363 amino acid protein, shares only 32% identical amino acid residues with AT1 receptor, although it also has a seven transmembrane domain topology. In adult mammalian kidneys, AT1 receptors predominate in the glomerular mesangium, proximal tubular epithelium, renomedullary interstitial cells in the inner stripe of the outer medulla and large preglomerular vessels except those in human and monkey where AT2 receptors predominate. By contrast, in foetal kidneys, AT2 receptors are the major subtype; however, this shows dramatic regulation during development. Physiological studies using AT1 selective antagonists show that the known actions of All on renal haemodynamics, glomerular filtration, and tubular sodium and water transport are mediated by this subtype of All receptors. In addition, AT1 receptors also mediate hypertrophic and mitogenic actions of All on cultured glomerular mesangial cells and proximal tubular epithelial cells, and on extra-cellular matrix accumulation in animal models of progressive renal diseases. By contrast, blockade of AT2 receptors has no effect on renal haemodynamics, tubular sodium reabsorption or growth properties of All. Overall, All exerts multiple actions in the kidney by interacting with different subtypes of All receptors located on multiple cellular sites.

Notes: 1. Renomedullary interstitial cells (RMIC), abundant throughout the medulla of the kidney, have been demonstrated to have binding sites for many vasoactive peptides, including atrial natriuretic peptide, endothelin, angiotensin II and bradykinin (BK). These observations would support the hypothesis that interactions between RMIC and vasoactive peptides are important in the regulation of renal function.2. We aimed to localize the BK B2 receptor binding site to RMIC in vivo and to also demonstrate that these receptors are biologically active in vitro.3. The present study demonstrates BK B2 binding sites on RMIC of the inner stripe of the outer medulla and the inner medulla of the rat kidney in vivo.4. We further demonstrate that the BK B2 radioligand [125I]-HPP-Hoe140 specifically bound to rat RMIC in vitro. In addition, reverse transcription–polymerase chain reaction detected the mRNA for the BK B2 receptor subtype in cell extracts.5. For RMIC in vitro, cAMP levels were increased at 1 min and cGMP levels were increased at 2 min after treatment with 10–10 and 10–7 mol/L BK, respectively. Inositol 1,4,5-trisphosphate was increased at 10 s treatment with both 10–6 and 10–7 mol/L BK.6. For RMIC in vitro, BK induced an increase in cell proliferation ([3H]-thymidine incorporation) and an increase in extracellular matrix synthesis (ECM; trans-[35S] incorporation), both effects mediated by BK B2 receptors.7. We conclude that BK B2 receptors are present on RMIC both in vivo and in vitro. These receptors are coupled to intracellular second messenger systems and, in vitro, their stimulation results in cellular proliferation and synthesis of ECM.