s of Posters and Free Communications Kidney Blood Press Res 1998;21:81–210 141

Because the data from the literature contain conflicting results regarding the role of renal nerves and angiotensin II in hypoxiainduced erythropoietin (EPO) secretion, we evaluated the effect of renal nerves and salt intake in rats on EPO secretion stimulated by carbon monoxide (CO). Serum levels and renal mRNA content of EPO were similarly elevated by exposure to different CO concentrations in a dose-dependent manner in rats with bilateral renal denervation (DNX) and in sham-denervated controls (INN). However, at 600 ppm CO, serum concentrations and mRNA of EPO were significantly higher in DNX compared with INN rats (p < 0.05). This increase of EPO secretion in DNX rats could be blocked by administration of neuropeptide Y (NPY) (p < 0.05), whereas the NPY receptor antagonist did not enhance EPO secretion in INN rats after CO exposure. Agonists and antagonists of beta-adrenergic receptors had no effect on EPO secretion. High-salt (HS) diet reduced EPO secretory response at 600 ppm CO by 55% compared with INN rats on normal salt diet (p < 0.01). In addition, DNX increased EPO secretion in rats on low-salt and HS diet, whereas plasma renin activity did not correlate with EPO levels under these experimental conditions. In summary, our data suggest that renal nerves contribute to the half-maximal EPO secretory response to CO exposure, possibly via NPY receptors.

Renin, the key element of the renin–angiotensin–aldosterone system, is mainly produced by and stored in the juxtaglomerular cells in the kidney. These cells are situated in the media of the afferent arteriole close to the vessel pole and can transform into smooth muscle cells and vice versa. In this study, the electrophysiological properties and the molecular identity of the K + channels responsible for the resting membrane potential (∼−60 mV) of the juxtaglomerular cells were examined. In order to increase the number of juxtaglomerular cells, afferent arterioles from NaCl‐depleted rats were used, and > 90% of the afferent arterioles were renin positive at the distal end of the arteriole. Whole‐cell and cell‐attached single‐channel patch‐clamp experiments showed that juxtaglomerular cells are endowed with a strongly inwardly rectifying K + channel (Kir). The channel was highly sensitive to inhibition by Ba 2+ (inhibition constant 37 μ m at 0 mV), but relatively insensitive to Cs + and, with 142 m m K + in the pipette, had a single‐channel conductance of 31.5 pS. Immunocytochemical studies showed the presence of Kir2.1 but no signal for Kir2.2 in the media of the afferent arteriole. In PCR analyses using isolated juxtaglomerular cells, the mRNA for Kir2.1 and Kir2.2 was detected. Collectively, the results show that Kir2.1 is the dominant component of the channel. The current carried by these channels plays a decisive role in setting the membrane potential of juxtaglomerular cells.

The dopamine D2-like receptor agonist quinpirole has been reported to lower blood pressure. This effect appears to be mediated via activation of presynaptic D2-like receptors inhibiting the stimulated neural norepinephrine release. The aim of the present study was to investigate the role of renal nerves and the renin-angiotensin system (RAS) in the blood pressure lowering effect of quinpirole. Therefore, clearance experiments using different doses of quinpirole (0.3 to 100 µg/kg/min) were performed in thiopental-anesthetized rats with intact kidneys (INN) or 5 to 7 days after bilateral renal denervation (DNX). The functional involvement of the RAS in the blood pressure lowering effect of quinpirole was determined in rats pretreated with a subpressor dose of angiotensin II (10 µg/kg/min) or in rats pretreated with the angiotensin II (AT1) receptor antagonist losartan, in a subdepressor dose (10 µg/kg/min).

Blood-tissue exchange and homeostasis within the organs depend on various interactions between endothelial and perivascular cells (Buniatian, 2001). Podocytes possess anatomical and cellular features intermediate between those of astrocytes and hepatic stellate cells (HSCs). Podocytes, like HSCs, are associated with fenestrated capillaries and, similar to astrocytes, interact with the capillaries via the basement membrane and participate in permeability-limiting ultrafiltration. The fact that podocytes come in direct contact with xenobiotics prompted us to investigate whether they express metallothionein (MT), an anticytotoxic system characteristic of astrocytes. In comparative studies, cryosections of 1- and 3-month-old rat kidney and adult rat brain, as well as podocytes and astrocytes from early and prolonged primary cultures of glomerular explants and newborn rat brain, respectively, were investigated. The cells were double-labeled with antiserum against glial fibrillary acidic protein (GFAP) and monoclonal antibody (MAb) against the lysine-containing epitope of Cd/Zn-MT-I (MAb MT) or MAb against alpha-actin. In kidney sections, MT immunoreactivity was detected in GFAP-positive glomerular cells and in interstitial fibroblasts. The pattern of staining for MT and GFAP in glomerular cells was similar to that of astrocytes in vivo. In glomerular cell cultures, MT was expressed in cobblestone-like podocytes which contained Wilms' tumor protein and lacked desmin. MT was upregulated at later culture periods, during which podocytes acquired features typical of undifferentiated astrocytes. This study hints at the existence of common regulatory mechanisms of blood-tissue interactions by neural and non-neural perivascular cells. These mechanisms appear to be used in an organ-specific manner.

s Kidney Blood Press Res 1999;22:189– 419 265 PND of dbb, membrane protein targeting defects were observed concerning the location of Na, K, ATPase and alkaline phosphatase. In Summary, in the mutant dbb the PNT is most severely affected by cyst formation associated with depression of proximal reabsorptive cell development.

The role of potassium intake in the response of kidney function and plasma renin activity (PRA) to systemic application of U37883A (4-morpholinecarboximidine-N-1-adamantyl-N’-cyclohexyl-hydrochloride), a putative blocker of ATP-sensitive potassium channels (K ATP ), and P1075 (N-cyano-N’-(1,1-dimethylpropyl)-N’’-pyridylguanidine), an opener of K ATP channels, was studied in the anesthetized rat. It was found that under normal potassium diet ( 0.7% K ), U37883A (15 mg/kg, i.v.) increased urinary flow rate (UV) and sodium excretion (UNaV), decreased urinary potassium excretion (UKV), and significantly diminished heart rate (HR) without affecting mean arterial blood pressure (MAP) or glomerular filtration rate (GFR). P1075 (10 µg/kg, i.v.) lowered UV, UNaV and UKV, at least in part due to the fall in MAP and GFR.PRA was diminished by U37883A and increased by P1075.Variation in potassium diet ( 0.04 or 2% K ) left the response in MAP, HR or GFR to both potassium channel modulators essentially unchanged. The reduction in renal excretion rates to P1075 also appeared unaffected, further supporting a predominant role of the change in MAP and GFR in this response. Variation in potassium diet, however, elicited the following alterations: (1) under both low and high potassium diet U37883A did no longer cause a significant natriuresis; (2) U37883A elicited a significant kaliuresis under high potassium diet , whereas potassium excretion remained essentially unchanged on very low levels under low potassium diet ; (3) the increase in PRA to P1075 was blunted under low potassium diet. Additional experiments provided evidence that P1075 releases renin from freshly isolated juxtaglomerular cells of rats on normal but not on low potassium diet . In summary, systemic potassium channel modulation employing U37883A or P1075, respectively, exerts distinct effects on blood pressure and heart rate independent of potassium diet. In contrast, potassium diet appears to be a determinant for the concomitant reponses in plasma renin activity and renal sodium and potassium excretion.

Freshly isolated rat juxtaglomerular cells (JGC) were superfused to study renin secretion rate (RSR) at the cellular level. Effluates from the superfusion chamber collected in 20-min intervals showed a time-dependent decline in RSR from 85.5 +/- 32 to 4.0 +/- 2.4 ng ANG I. ml-1. h-1. mg protein-1. min-1 within 100 min of collection (mean +/- SE, n = no. of JGC preparations/superfusion chambers = 9/18). Addition of adenosine deaminase type II (ADA II, 3 U/1.4 mg protein) to the superfusion medium increased RSR more than fourfold to 402 +/- 100 ng in the first collection period, which dropped to 237.5 +/- 67 ng ANG I. ml-1. h-1. mg protein-1. min-1 (n = 9/18) within 100 min. This ADA II effect was rapid in onset and fully reversible. When the purified ADA type VII, with a 40-fold higher specific activity, was added to the superfusate, RSR was increased only by 96 +/- 17.8% compared with controls. This ADA VII (5 U/30 microgram) effect could be mimicked by the selective adenosine A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10(-6) mol/l). Since albumin stimulated RSR in a concentration-dependent fashion, to an extent similar to that of ADA II, we assume that the ADA II effect was largely unspecific in nature. We conclude that 1) superfusion of isolated JGC from rats is suitable for investigations of renin secretion at the cellular level, 2) the increase in RSR by ADA II appears to be only in part due to deamination of endogenously generated adenosine, and 3) albumin in the superfusate induces a similar stimulatory effect as ADA II.

In this study the presence of glial fibrillary acidic protein (GFAP) in kidney is for the first time demonstrated in cryostat sections and cultures of isolated glomerular explants derived from rat kidneys. In double immunolabelling analysis of adult rat kidney sections using antiserum against GFAP and monoclonal antibody (mAb) against vimentin or desmin, the presence of immunoreactivity for GFAP could be observed in the glomerulus of the kidney and vascular cells situated in the peritubular space which expressed vimentin and desmin. Labelling of the sections with absorbed antiserum against GFAP completely abolished the staining in all these cells. The mAb against GFAP, clone GF12.24 which is known to label GFAP both in neural and non-neural cells, recognised its antigen only in the cells located in glomeruli. The investigations performed on early 2- or 3-day-old cultures from glomerular explants revealed different patterns of staining for GFAP in mesangial cells and podocytes: weak filamentous in mesangial cells and a strong non-filamentous perinuclear pattern in podocytes. Due to prominent perinuclear expression in podocytes GFAP may be considered as a marker of these cells. A different pattern of distribution of immunoreactivity for GFAP in podocytes and mesangial cells might be due to function-related posttranslational modifications of GFAP resulting in assembly or disassembly of GFAP filaments. The different pattern of staining for GFAP in the podocytes and mesangial cells, cells which exert a different influence on the capillaries of the glomeruli, suggests a role for GFAP in regulation of the tension and permeability of vascular walls. Previous investigations and present studies hint at GFAP as being a general marker of perivascular cells.

Guinea-pig oxyntic cell tubulin has been isolated andin vitro aggregation has been studied. The spontaneous assembly of isolated tubulin was significantly accelerated and increased bt 1 mmol/l GTP. Histamine and forskolin increased tubulin polymerization only when detergent dispersed oxyntic cells or crude membranes were added. The forskolin response occurred very rapidly with an EC50 of approximately 30 μmol/l and did not require GTP. Histamine promoted tubulin aggregation with an EC50 of about 5 μmol/l only in the presence of GTP. Ranitidine completely inhibited the effects of histamine. From these data it is suggested that, in the oxyntic cell, histamine H2-receptor activated adenylate cyclase and the corresponding increase in cAMP play a role in eliciting characteristic ultrastructural changes by initiating formation of microtubules as a first step in the cascade of events leading to an increase in the secretory surface area.

Intravenous (i.v.) administration of nicotine in conscious cats significantly stimulated basal gastric acid output. The effect was completely blocked by atropine and ranitidine. Submaximally stimulated gastric acid secretion was not further increased by nicotine. In isolated guinea pig parietal cells nicotine significantly increased basal acid secretion by about 20% and potentiated the response to maximally effective concentrations of histamine but had no influence on the carbachol response. In isolated parietal cells stimulated either by nicotine, histamine or both, atropine pretreatment increased or inhibited the acid response in concentration-dependent manner. From these data, it is concluded that nicotine had direct stimulatory effects on isolated parietal cells and potentiated the histamine mediated response in the isolated cell preparation but not in the intact animal model.

The role of prostaglandins in somatostatin mediated gastric inhibitory effects has been investigated in conscious cats. The effect of somatostatin on pentagastrin-, insulin- and histamine plus bethanechol-stimulated gastric acid and pepsin secretion was determined with and without indomethacin pretreatment. Somatostatin significantly inhibited acid and pepsin secretion and this effect was not diminished by cyclo-oxygenase inhibition. It is concluded that there is no evidence that endogenous prostaglandins mediate the inhibitory effects of somatostatin on gastric acid and pepsin secretion in the cat.

In isolated guinea-pig parietal cells pretreated for 60 min with the H2-antagonist ranitidine, the antimitotic agents colchicine and vinblastine, the microfilament-disrupting agent cytochalasin B resulted in a concentration-dependent inhibition of histamine-stimulated acid secretion up to 80%. Ranitidine reduced histamine binding to the membrane located H2-receptor. The anti-cytoskeletal agents inhibited the cellular histamine uptake but did not effect the histamine methyltransferase activity which was significantly reduced by ranitidine. The data suggest that cytoskeletal elements like microtubules and microfilaments are of very specific functional significance not only in the secretory process of the parietal cell but also for cellular transport mechanisms.