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H Pavenstädt

Publications and source records attributed to H Pavenstädt.

At least 19 recordsLinked to original sources
PubMed2006

Renal cortical regulation of COX-1 and functionally related products in early renovascular hypertension (rat).

Renal volume regulation is modulated by the action of cyclooxygenases (COX) and the resulting generation of prostanoids. Epithelial expression of COX isoforms in the cortex directs COX-1 to the distal convolutions and cortical collecting duct, and COX-2 to the thick ascending limb. Partly colocalized are prostaglandin E synthase (PGES), the downstream enzyme for renal prostaglandin E(2) (PGE(2)) generation, and the EP receptors type 1 and 3. COX-1 and related components were studied in two kidney-one clip (2K1C) Goldblatt hypertensive rats with combined chronic ANG II or bradykinin B(2) receptor blockade using candesartan (cand) or the B(2) antagonist Hoechst 140 (Hoe). Rats (untreated sham, 2K1C, sham + cand, 2K1C + cand, sham + Hoe, 2K1C + Hoe) were treated to map expression of parameters controlling PGE(2) synthesis. In 2K1C, cortical COX isoforms did not change uniformly. COX-2 changed in parallel with NO synthase 1 (NOS1) expression with a raise in the clipped, but a decrease in the nonclipped side. By contrast, COX-1 and PGES were uniformly downregulated in both kidneys, along with reduced urinary PGE(2) levels, and showed no clear relations with the NO status. ANG II receptor blockade confirmed negative regulation of COX-2 by ANG II but blunted the decrease in COX-1 selectively in nonclipped kidneys. B(2) receptor blockade reduced COX-2 induction in 2K1C but had no clear effect on COX-1. We suggest that in 2K1C, COX-1 and PGES expression may fail to oppose the effects of renovascular hypertension through reduced prostaglandin signaling in late distal tubule and cortical collecting duct.

Adrenergic beta-Antagonists↗
PubMed2006

The C/EBP homologous protein CHOP (GADD153) is an inhibitor of Wnt/TCF signals.

CHOP (GADD153) is a protein of the C/EBP family of transcriptional regulators, which dimerizes with other C/EBP members and changes their DNA-binding and transactivation properties. It induces growth arrest and apoptosis after endoplasmatic reticulum stress or DNA damage. CHOP is also expressed during early embryogenesis and upregulated in tumour tissues with defective Wnt signals. We report here that CHOP functions as a specific inhibitor of Wnt/T-cell factor (TCF) signalling. CHOP inhibits TCF-dependent transcription in human embryonic and colon cancer cell lines. Injection of CHOP mRNA into early Xenopus laevis embryos suppresses dorsal organizer formation and inhibits secondary axis formation and TCF-dependent transcription in response to Wnt-8, Dishevelled, beta-Catenin and TCF-VP16. In embryos and human cells, this inhibition depends on the N-terminal transactivation domain of CHOP, whereas the C-terminal dimerization domain is dispensable. CHOP binds to TCF factors, thereby preventing the binding of TCF to its DNA recognition site. Our findings demonstrate a novel function of CHOP as a Wnt repressor.

Amino Acid Motifs↗
PubMed2001

Regulation of slowly activating potassium current (I(Ks)) by secretin in rat pancreatic acinar cells.

1. The secretagogue-activated K(+) conductance is indispensable for the electrogenic Cl(-) secretion in exocrine tissue. In this study, we investigated the effect of secretin and other cAMP-mediated secretagogues on the slowly activating voltage-dependent K(+) current (I(Ks)) of rat pancreatic acinar cells (RPAs) with the whole-cell patch clamp technique. 2. Upon depolarization, RPAs showed I(Ks) superimposed upon the instantaneous background outward current. Secretin (5 nM), vasoactive intestinal peptide (5 nM), forskolin (5 microM), isoprenaline (10 microM) or 3-isobutyl-1-methylxanthine (IBMX, 0.1 mM) increased the amplitude of I(Ks) two- to fourfold. 3. The physiological concentration of secretin (50 pM) had a relatively weak effect on I(Ks) (160 % increase), which was significantly enhanced by transient co-stimulation with carbachol (CCh) (10 microM). However, the secretin-induced production of cAMP, which was measured by enzyme-linked immunosorbent assay, was not augmented by co-stimulation with CCh. 4. This study is the first to demonstrate the regulation of K(+) channels in RPAs by cAMP-mediated agonists. The I(Ks) channel is a common target for both Ca(2+) and cAMP agonists. The vagal stimulation under the physiological concentration of secretin facilitates I(Ks), which provides an additional driving force for Cl(-) secretion.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Extracellular nucleotides regulate cellular functions of podocytes in culture.

Extracellular nucleotides are assumed to be important regulators of glomerular functions. This study characterizes purinergic receptors in podocytes. The effects of purinergic agonists on electrophysiological properties and the intracellular free Ca(2+) concentration of differentiated podocytes were examined with the patch-clamp and fura 2 fluorescence techniques. mRNA expression of purinergic receptors was investigated by RT-PCR. Purinergic agonists depolarized podocytes. Purinergic agonists similarly increased intracellular free Ca(2+) concentration of podocytes. The rank order of potency of various nucleotides on membrane voltage and free cytosolic calcium concentration was UTP approximately UDP > [adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S)] > ATP > 2-methylthioadenosine 5'-triphosphate (2-MeS-ATP) > 2'- and 3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP) > ADP-beta-S. alpha,beta-Me-ATP was without effect. In the presence of UTP, BzATP did not cause an additional depolarization of podocytes. Incubation of cells with ATP or BzATP did not induce lactate dehydrogenase release. In RT-PCR studies, mRNAs of the P2Y(1), P2Y(2), P2Y(6), and P2X(7) receptors were detected within glomeruli and podocytes. The data indicate that extracellular nucleotides modulate podocyte function mainly by an activation of both P2Y(2) and P2Y(6) receptors.

Adenosine Triphosphate↗
PubMed2000

Aquaporin 3 cloned from Xenopus laevis is regulated by the cystic fibrosis transmembrane conductance regulator.

The cystic fibrosis transmembrane conductance regulator (CFTR) is essential for epithelial electrolyte transport and has been shown to be a regulator of epithelial Na(+), K(+), and Cl(-) channels. CFTR also enhances osmotic water permeability when activated by cAMP. This was detected initially in Xenopus oocytes and is also present in human airway epithelial cells, however, the mechanisms remain obscure. Here, we show that CFTR activates aquaporin 3 expressed endogenously and exogenously in oocytes of Xenopus laevis. The interaction requires stimulation of wild type CFTR by cAMP and an intact first nucleotide binding domain as demonstrated for other CFTR-protein interactions.

Amino Acid Sequence↗
PubMed2000

Inwardly rectifying K+ channels in the basolateral membrane of rat pancreatic acini.

Previous studies of the whole-cell K+ conductance suggest the presence of inwardly rectifying K+ channels (Kir) in rat pancreatic acini (RPAs). Here we investigate the properties of Kir of RPAs using patch-clamp techniques. The whole-cell current-to-voltage relationship of freshly isolated RPAs was steeper for inward currents than for outward currents when the extracellular K+ concentration ([K+]o) was raised. With a high [K+]o (145 mM), external application of Ba2+ and Cs+ blocked the inward K+ current in a voltage-dependent manner. The apparent IC50 of Ba2+ was 8.5+/-1.9 microM and 1.1+/-0.2 microM at -70 mV and -130 mV, respectively (n=5). The IC50 of Cs+ was 3.5+1.1 mM and 0.2+0.1 mM at -60 mV and -120 mV, respectively (n=4). Application of Ba2+ (0.1 mM) to the extracellular solution reversibly depolarized RPAs from -43+1.1 mV to -37+/-1.2 mV (n=20). In the cell-attached configuration with 145 mM KC1 in the pipette solution, we observed inwardly rectifying channels with a high open probability (PO) of 0.85+/-0.02 (n=6) and a slope conductance (Gs) of 30+/-2.8 pS (n=13). The same type of channel was observed in the outside-out patch. We could also observe a very small conductance K+ channel which was resistant to 0.1 mM Ba2+ and did not show inward rectification (n=11). RT-PCR analysis of RPA confirmed the presence of transcripts for Kir2.1, Kir2.3 and Kir7.1 subfamilies as molecular candidates for the observed channels. The above results demonstrate the presence of Kir channels in the basolateral membrane of the RPA, which may be important for the K+ recycling process during electrolyte secretion as well as for maintaining a hyperpolarized membrane.

Animals↗
PubMed2000

Angiotensin II increases the intracellular calcium activity in podocytes of the intact glomerulus.

UNLABELLED: Angiotensin II increases the intracellular calcium activity in podocytes of the intact glomerulus. BACKGROUND: Knowledge about biological functions of podocytes in the glomerulus is limited because of its unique anatomical location. Here we introduce a new method for measuring the intracellular calcium activity ([Ca2+]i) in the podocyte in the intact glomerulus. METHODS: With the help of fluorescence high-resolution digital imaging and a recently developed ultraviolet laser-scanning microscope, [Ca2+]i was measured in fura-2-loaded glomeruli and single podocytes of intact microdissected rat glomeruli. RESULTS: Angiotensin II (Ang II) increased [Ca2+]i reversibly in a biphasic and concentration-dependent manner. In contrast to Ang II, bradykinin, thrombin, arginine vasopressin, and serotonin did not change [Ca2+]i in the glomerulus. At reduced extracellular Ca2+ activity, Ang II released [Ca2+]i from intracellular stores, but the second phase, corresponding to a Ca2+ influx from the extracellular space, was absent. The L-type Ca2+ channel blocker nicardipine did not influence the Ang II-mediated [Ca2+]i increase, and an increase of the extracellular K+ concentration did not change [Ca2+]i in the glomerulus. The angrotensin II type I (AT1) receptor antagonist losartan inhibited the Ang II-mediated [Ca2+]i increase. Confocal [Ca2+]i measurements using fura-2 or fluo-3 or fluo-4 on the single cell level show that some of the Ang II-mediated [Ca2+]i response originated from podocytes. Costaining with calcein allowed the identification of podocytes because of the characteristic morphology and location in relationship to the capillary network. CONCLUSIONS: These data suggest that podocytes in the intact glomerulus respond to Ang II with an increase of [Ca2+]i via an AT1 receptor.

Angiotensin II↗
PubMed2000

Roles of the podocyte in glomerular function.

The podocyte is the most differentiated cell type in the glomerulum, which forms a crucial component of the glomerular filtration barrier. It has been assumed that podocyte foot processes counteract the elastic force of the glomerular basement membrane and that vasoactive hormones may regulate the contractile state of their foot processes and thereby modulate the ultrafiltration coefficient K(f). Podocyte damage leads to proteinuria, and podocyte injury occurs in many glomerular diseases, which may progress to chronic renal failure. The understanding of the regulation of physiological properties of the podocyte and the mechanisms of its cellular response to injury may thus provide a clue to the understanding of the pathogenesis of proteinuria and glomerular diseases. In the past it was difficult to study cellular functions in this cell type, because of its unique anatomic location and the difficulty in characterizing podocytes in cell culture. However, recent advances in physiological, molecular biological, and cell culture techniques have increased the knowledge of the role of the podocyte in glomerular function. The present review attempts to outline new aspects of podocyte function in the glomerulum.

Adenosine Triphosphate↗
PubMed2000

Amino acid transport in podocytes.

It has recently been shown that formation of podocyte foot processes is dependent on a constant source of lipids and proteins (Simons M, Saffrich R, Reiser J, and Mundel P. J Am Soc Nephrol 10: 1633-1639, 1999). Here we characterize amino acid transport mechanisms in differentiated cultured podocytes and investigate whether it may be disturbed during podocyte injury. RT-PCR studies detected mRNA for transporters of neutral amino acids (ASCT1, ASCT2, and B(0/+)), cationic AA (CAT1 and CAT3), and anionic AA (EAAT2 and EAAT3). Alanine (Ala), asparagine, cysteine (Cys), glutamine (Gln), glycine (Gly), leucine (Leu), methionine (Met), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), glutamic acid (Glu), arginine (Arg), and histidine (His) depolarized podocytes and increased their whole cell conductances. Depletion of extracellular Na(+) completely inhibited the depolarization induced by Ala, Gln, Glu, Gly, Leu, and Pro and decreased the depolarization induced by Arg and His, indicating the presence of Na(+)-dependent amino acid transport. Incubation of podocytes with 100 microg/ml puromycin aminonucleoside for 24 h significantly attenuated the effects induced by the various amino acids by approximately 70%. The data indicate the existence of different amino acid transporter systems in podocytes. Alteration of amino acid transport may participate in podocyte injury and disturbed foot process formation.

Amino Acids↗
PubMed1999

Hydrogen peroxide activates ion currents in rat mesangial cells.

BACKGROUND: Hydrogen peroxide (H2O2) is an important mediator of glomerular injury, which induces proliferation and cell contraction in mesangial cells. The aim of this study was to investigate whether and which ion currents are activated during the early cellular responses to H2O2, and to study possible mechanisms of their activation. METHODS: The effect of H2O2 on membrane voltage of mesangial cells in short-term culture was investigated with the patch clamp technique in the fast whole cell configuration. RESULTS: H2O2 contracted mesangial cells and induced a concentration-dependent biphasic membrane voltage response. One hundred micromol/liter H2O2 led to a hyperpolarization of mesangial cells from -45 +/- 1 to -55 +/- 1 mV, which was followed by a sustained depolarization to -20 +/- 3 mV. The hyperpolarization induced by H2O2 was completely blocked by the K+ channel blocker Ba2+. In the presence of a low extracellular Cl- concentration (32 mmol/liter), the depolarization induced by H2O2 was significantly increased. The H2O2-induced depolarization was inhibited by 100 micromol/liter of the disulfide-reducing agent dithiothreitol, whereas higher concentrations of dithiothreitol (1 mmol/liter) were required to partially inhibit the hyperpolarization. Protein kinase C inhibitors blocked the H2O2-induced depolarization, but not the hyperpolarization. CONCLUSIONS: The data indicate that H2O2 leads to a biphasic membrane voltage response in mesangial cells: an initial transient hyperpolarization, which is due to the activation of a K+ conductance, and a subsequent depolarization, which is, at least in part, due to the activation of a Cl- conductance. The oxidation of thiol groups by H2O2 is involved in the membrane voltage response, and the depolarization may be regulated by protein kinase C.

Animals↗
PubMed1999

Polycations induce calcium signaling in glomerular podocytes.

BACKGROUND: The neutralization of the polyanionic surface of the podocyte by perfusion of kidneys with polycations, such as protamine sulfate, leads to a retraction of podocyte foot processes and proteinuria. This study investigates the effects of protamine sulfate or anionic, neutral, or cationic dextrans on the cytosolic calcium activity ([Ca2+]i) in podocytes. METHODS: [Ca2+]i was measured in single cultured differentiated mouse podocytes with the fluorescence dye fura-2/AM. RESULTS: Protamine sulfate caused a concentration-dependent and partially reversible increase of [Ca2+]i (EC50 approximately 1.5 micromol/liter). Pretreatment of the cells with heparin (100 U/liter) inhibited the protamine sulfate-mediated increase of [Ca2+]i. Like protamine sulfate, diethylaminoethyl dextran (DEAE-dextran) concentration dependently increased [Ca2+]i in podocytes (EC50 approximately 20 nmol/liter), whereas dextran sulfate or uncharged dextran (both 10 micromol/liter) did not influence [Ca2+]i. A reduction of the extracellular Ca2+ concentration (from 1 mmol/liter to 1 micomol/liter) partially inhibited the protamine sulfate and the DEAE-dextran-induced [Ca2+]i response. Flufenamate (100 micromol/liter) or Gd3+ (10 micromol/liter), which are known to inhibit nonselective ion channels, did not influence the [Ca2+]i increase induced by protamine sulfate. In the presence of thapsigargin (50 nmol/liter), an inhibitor of the endoplasmic reticulum Ca2+-ATPase, both protamine sulfate and DEAE-dextran increased [Ca2+]i. CONCLUSIONS: The data indicate that polycations increase podocyte [Ca2+]i. The increase of [Ca2+]i may be an early event in the pathogenesis of protamine sulfate-mediated retraction of podocyte foot processes.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1999

Dopamine depolarizes podocytes via a D1-like receptor.

BACKGROUND: Dopamine influences glomerular haemodynamics and dopamine receptors have been demonstrated in the glomerulus, but little is known about the cellular effects of dopamine in glomerular cells. The aim of this study was to investigate the influence of dopamine on the cellular functions of podocytes. METHODS: The effect of dopamine on membrane voltage was investigated in differentiated mouse podocytes. The membrane voltage was measured using the patch clamp technique. Reverse transcribed-polymerase chain reaction (RT-PCR) studies were performed to investigate the expression of dopamine receptor mRNA in mouse glomeruli and podocytes. RESULTS: The addition of dopamine (100 nM-1000 microM) caused a concentration-dependent depolarization of podocytes (EC50 is approximate to 10 microM). Like dopamine, the selective agonist of the D1-like receptor, SKF 82958, depolarized podocytes in a concentration-dependent manner. (EC50 is approximate to 50 microM). SKF 82958 stimulated a time-and concentration-dependent accumulation of cyclic adenosine 3',5'-monophosphate (cAMP) in podocytes (EC50 is approximate to microM). RT-PCR studies with primers derived from mouse sequences amplified mouse mRNA for the D1-like and the D2-like receptor in glomeruli, which were obtained by the sieve technique, whereas only mRNA for the D1-like receptor was detected in cultured mouse podocytes. CONCLUSION: The data indicate that dopamine induces a cAMP-dependent depolarization via a D1-like receptor in podocytes.

Animals↗
PubMed1999

Characterization of prostanoid receptors in podocytes.

Prostaglandins participate in the regulation of important glomerular functions and are involved in the pathogenesis of glomerular diseases. This study investigates the influence of prostaglandins on membrane voltage, ion conductances, cAMP accumulation, and cytosolic calcium activity ([Ca2+]i) in differentiated podocytes. Prostaglandin E2 (PGE2) caused a concentration-dependent depolarization and an increase of the whole cell conductance in podocytes (EC50 approximately 50 nM). Compared with PGE2, the EP2/EP3/EP4 receptor agonist 11-deoxy-PGE1 caused an equipotent depolarization, whereas the DP receptor agonist BW 245 C, the EP1/EP3 receptor agonist sulprostone, and the IP receptor agonist iloprost were at least 100 to 1000 times less potent than PGE2. The EP2 receptor agonist butaprost did not change membrane voltage of podocytes. The depolarizing effect of PGE2 was increased in an extracellular solution with a reduced Cl- concentration (from 145 to 32 mM). PGE2 and the prostaglandin agonists, but not the IP receptor agonist iloprost and the EP2 receptor agonist butaprost, induced a time- and concentration-dependent cAMP accumulation in podocytes. In fura-2 fluorescence experiments, PGE2, sulprostone, PGF2alpha, fluprostenol (a potent FP agonist), and U-46619 (a selective thromboxane A2 agonist) induced a biphasic increase of [Ca2+]i in 60 to 80% of podocytes. In reverse transcription-PCR studies, podocyte mRNA for the EP1, EP4, FP, and TP receptor could be amplified. These data indicate that in podocytes, PGE2 regulates distinct cellular functions via the EP1 and EP4 receptor, thereby increasing [Ca2+]i and cAMP, respectively. Furthermore, PGF1alpha and U-46619 increase [Ca2+]i via their specific receptors.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

NAD(P)H oxidase activity in cultured human podocytes: effects of adenosine triphosphate.

Reactive oxygen species contribute to glomerular damage and proteinuria. In this study, we show that cultured human podocytes produce superoxide in response to extracellular adenosine triphosphate (ATP), and we identified the oxidases involved in this process. Adenosine triphosphate (10-4 M for 4 hr) raised superoxide production from 1.28 +/- 0.15 to 2.67 &/- 0.34 nmol/mg protein/min. Studies with podocyte homogenates revealed activation of both nicotinamide adenine dinucleotide (NADH; from 2.65 +/- 0.23 to 7.43 +/- 0.57) and nicotinamide adenine dinucleotide phosphate (NADPH) dependent oxidases [from 1.74 +/- 0.13 to 4.05 +/- 0.12 (nmol O2/mg protein/min)] by ATP. Activity of xanthine-oxidases was low and unchanged by ATP. Activation of the plasma-membrane bound NAD(P)H oxidases by ATP was time and dose dependent. Reverse transcribed-polymerase chain reaction (RT-PCR) studies with primers derived from monocyte sequences amplified mRNA for the NADPH oxidase subunits p22phox, p47phox, gp91phox, and p67phox, and the latter was transiently increased by ATP. Experiments with actinomycin D and cycloheximide suggested that ATP modulates enzyme activity at the transcriptional and translational levels. In conclusion, NAD(P)H dependent, membrane associated oxidases represent the major superoxide source in human podocytes. Activation of NAD(P)H oxidase by ATP might be secondary to increased mRNA expression of the NADPH oxidase subunit gp67phox.

Adenosine Triphosphate↗
PubMed1998

Angiotensin II modulates cellular functions of podocytes.

Angiotensin II modulates cellular functions of podocytes. The aim of this study was to examine the effects of angiotensin II (Ang II) on membrane voltage (Vm) and cytosolic calcium activity ([Ca2+]i) of rat podocytes. To approach better the in vivo situation, we have developed an experimental approach that allows podocytes to be studied in the intact microdissected glomerulus. Ang II depolarized podocytes in the glomerulus (EC50 15 nM, N = 49). Like podocytes in the glomerulus, podocytes in short-term culture also depolarized in response to Ang II (10 nM, N = 5). Ang II increased [Ca2+]i in podocytes in culture (EC50 3 nM, N = 229). In a solution with reduced extracellular [Ca2+] (10 microM), Ang II-mediated [Ca2+]i increase was significantly reduced by 60% +/- 20% (N = 12). Flufenamate, an inhibitor of nonselective ion channels, inhibited Ang II-mediated increase of [Ca2+]i (IC50 20 microM, N = 29). The Ang subtype 1 (AT1) receptor antagonist losartan inhibited both Ang II-mediated depolarization and [Ca2+]i increase in podocytes (N = 5 to 35). Our results support the concept that Ang II might influence podocyte function directly via an AT1 receptor.

Angiotensin II↗
PubMed1998

Bradykinin stimulates the intracellular calcium activity in human mesothelial cells.

AIM: The aim of this study was to investigate the influence of bradykinin on the intracellular calcium activity ([Ca2+]i) in human mesothelial cells in culture. RESULTS: Bradykinin (1-1000 nmol/l) caused a concentration-dependent and reversible increase of [Ca2+]i in mesothelial cells (n = 94); 10 nmol/l bradykinin increased [Ca2+]i from 23 +/- 9 to 670 +/- 170 nmol/l (n = 36). The pattern of the bradykinin-induced [Ca2+]i increase was biphasic with a transient [Ca2+]i peak, which was followed by a sustained [Ca2+]i plateau. The bradykinin-mediated [Ca2+]i plateau, but not the peak, was inhibited in a solution with an extracellular reduced Ca2+ concentration (from 1000 to 1 micromol/l, n = 11). Flufenamate (> or = 10 micromol/l), an inhibitor of non-selective ion channels abolished the bradykinin-mediated increase of [Ca2+], whereas the L-type Ca2+ channel blocker nicardipine (10 micromol/l) had no effect (n = 3-5). The [Ca2+]i response to bradykinin was inhibited by the BK2 antagonist Hoe 140 (IC50 +/- k7 nmol/l, n = 30). CONCLUSIONS: The data indicate that bradykinin stimulates [Ca2+]i in mesothelial cells by a release of Ca2+ from intracellular stores and an influx from Ca2+ through non-selective channels via a BK2 receptor.

Bradykinin↗