Proteinuria and increased renal reabsorption of NaCl characterize the nephrotic syndrome. Here, we show that protein-rich urine from nephrotic rats and from patients with nephrotic syndrome activate the epithelial sodium channel (ENaC) in cultured M-1 mouse collecting duct cells and in Xenopus laevis oocytes heterologously expressing ENaC. The activation depended on urinary serine protease activity. We identified plasmin as a urinary serine protease by matrix-assisted laser desorption/ ionization time of-flight mass spectrometry. Purified plasmin activated ENaC currents, and inhibitors of plasmin abolished urinary protease activity and the ability to activate ENaC. In nephrotic syndrome, tubular urokinase-type plasminogen activator likely converts filtered plasminogen to plasmin. Consistent with this, the combined application of urokinase-type plasminogen activator and plasminogen stimulated amiloride-sensitive transepithelial sodium transport in M-1 cells and increased amiloride-sensitive whole-cell currents in Xenopus laevis oocytes heterologously expressing ENaC. Activation of ENaC by plasmin involved cleavage and release of an inhibitory peptide from the ENaC ␥ subunit ectodomain. These data suggest that a defective glomerular filtration barrier allows passage of proteolytic enzymes that have the ability to activate ENaC.

The aspartyl-protease renin is the key regulator of the renin-angiotensin-aldosterone system, which is critically involved in salt, volume, and blood pressure homeostasis of the body. Renin is mainly produced and released into circulation by the so-called juxtaglomerular epithelioid cells, located in the walls of renal afferent arterioles at the entrance of the glomerular capillary network. It has been known for a long time that renin synthesis and secretion are stimulated by the sympathetic nerves and the prostaglandins and are inhibited in negative feedback loops by angiotensin II, high blood pressure, salt, and volume overload. In contrast, the events controlling the function of renin-secreting cells at the organ and cellular level are markedly less clear and remain mysterious in certain aspects. The unravelling of these mysteries has led to new and interesting insights into the process of renin release.

Little is known about prostaglandin F2␣ in cardiovascular homeostasis. Prostaglandin F2␣ dose-dependently elevates blood pressure in WT mice via activation of the F prostanoid (FP) receptor. The FP is expressed in preglomerular arterioles, renal collecting ducts, and the hypothalamus. Deletion of the FP reduces blood pressure, coincident with a reduction in plasma renin concentration, angiotensin, and aldosterone, despite a compensatory upregulation of AT1 receptors and an augmented hypertensive response to infused angiotensin II. Plasma and urinary osmolality are decreased in FP KOs that exhibit mild polyuria and polydipsia. Atherogenesis is retarded by deletion of the FP, despite the absence of detectable receptor expression in aorta or in atherosclerotic lesions in Ldlr KOs. Although vascular TNF ␣, inducible nitric oxide enzyme and TGF ␤ are reduced and lesional macrophages are depleted in the FP/Ldlr double KOs, this result reflects the reduction in lesion burden, as the FP is not expressed on macrophages and its deletion does not alter macrophage cytokine generation. Blockade of the FP offers an approach to the treatment of hypertension and its attendant systemic vascular disease.hypertension ͉ renin ͉ PGF2␣ receptor ͉ juxtaglomerular granular cell ͉ water metabolism C ontrol of hypertension has contributed to a decline of cardiovascular morbidity and mortality. Therapies have targeted neurohumoral mechanisms, such as the sympathoadrenal and renin-angiotensin-aldosterone systems (RAAS) as well as downstream effectors and volume control. Elevated blood pressure (BP) cosegregates with clinical cardiovascular events and randomized trials have revealed the efficacy of antihypertensive drugs to reduce the risk of stroke and myocardial infarction (1). Angiotensin II activates and up-regulates NADPH oxidase (2), augmenting oxidant stress and vascular dysfunction. Both pharmacological and genetic disruption of elements of the RAAS decreases BP and retards atherogenesis (3-5).Prostaglandins (PGs) also contribute to BP homeostasis. Elevation of BP complicates the use of nonsteroidal antiinflammatory drugs and relates to the degree of inhibition of cyclooxygenase (COX)-2 and the selectivity with which it is attained (6). Genetic and pharmacological manipulations suggest that products of COX-1 may elevate BP (7), although the impact of manipulating the PG cascade is conditioned by genetic background in mice (8). Prostacyclin (PGI 2 ) is a potent renin secretagogue (9), and its biosynthesis is increased markedly in pregnancy, a high-renin but hypotensive condition; its biosynthesis is depressed in pregnancy-induced hypertension (10). Deletion of its I prostanoid receptor (the IP) reduces BP in renoprival models of high-renin hypertension in rodents (11). PGI 2 is also a vasodilator and promotes sodium excretion; indeed, salt-sensitive hypertension characterizes IP-KO mice in some genetic backgrounds (12). PGF 2␣ is derived mainly from COX-1 in the female reproductive system, where it is required for normal parturition ...

Abstract-We tested the hypothesis that cGMP stimulates renin release through inhibition of the cAMP-specific phosphodiesterase 3 (PDE3) in isolated rat juxtaglomerular (JG) cells. In addition, we assessed the involvement of PDE4 in JG-cell function. JG cells expressed PDE3A and PDE3B, and the PDE3 inhibitor trequinsin increased cellular cAMP content, enhanced forskolin-induced cAMP formation, and stimulated renin release from incubated and superfused JG cells. Trequinsin-mediated stimulation of renin release was inhibited by the permeable protein kinase A antagonist Rp-8-CPT-cAMPS. PDE4C was also expressed, and the PDE4 inhibitor rolipram enhanced cellular cAMP content. Dialysis of single JG cells with cAMP in whole-cell patch-clamp experiments led to concentration-dependent, biphasic changes in cell membrane capacitance (C m ) with a marked increase in C m at 1 mol/L, no net change at 10 mol/L, and a decrease at 100 mol/L cAMP. cGMP also had a dual effect on C m at 10-fold higher concentration compared with cAMP. Trequinsin, milrinone, and rolipram mimicked the effect of cAMP on C m . Trequinsin, cAMP, and cGMP enhanced outward current 2-to 3-fold at positive membrane potentials. The effects of cAMP, cGMP, and trequinsin on C m and cell currents were abolished by inhibition of protein kinase A with Rp-cAMPs. We conclude that degradation of cAMP by PDE3 and PDE4 contributes to regulation of renin release from JG cells. Our data provide evidence at the cellular level that stimulation of renin release by cGMP involves inhibition of PDE3 resulting in enhanced cAMP formation and activation of the cAMP sensitive protein kinase. Key Words: juxtaglomerular apparatus Ⅲ renin Ⅲ exocytosis Ⅲ cGMP Ⅲ phosphodiesterase T he main rate-limiting step controlling the activity of the circulating renin-angiotensin system is the release of active renin from juxtaglomerular (JG) cells of the afferent glomerular arterioles in the kidney. Cyclic nucleotides are critical second messengers that determine renin secretory rate. Hormones, neurotransmitters, and autacoids that raise the intracellular production of cAMP stimulate renin secretion and renin mRNA levels. 1,2 Agonists coupled to cGMP formation have been reported both to stimulate and inhibit renin release. [3][4][5][6][7] At present, the response to cGMP is considered to be determined by the predominance of one of several targets for cGMP in JG cells. 7,8 The concentrations of cyclic nucleotides in cells are determined by the rate of synthesis by cyclases and by the rate of degradation by specific cyclic nucleotide phosphodiesterases (PDEs). 9 Drugs like theophylline, which inhibit PDEs unspecifically, increase renin secretion in vivo and potentiate the renin-secretory response to ␤-adrenoceptor stimulation. 10 This suggests a basal phosphodiesterase activity in JG cells. Presently, at least 11 different isoforms of PDEs are recognized. They are encoded by different genes and have different substrate specificity (cAMP or cGMP or both) and regulatory mechanisms (cAMP, cGMP, Ca 2ϩ...

Abstract-In the present study, we tested whether the ␣ 1A subunit, which encodes a neuronal isoform of voltage-dependent Ca 2ϩ channels (VDCCs) (P-/Q-type), was present and functional in vascular smooth muscle and renal resistance vessels. By reverse transcription-polymerase chain reaction and Southern blotting analysis, mRNA encoding the ␣ 1A subunit was detected in microdissected rat preglomerular vessels and vasa recta, in cultures of rat preglomerular vascular smooth muscle cells (