Biomedical subjects

A Henger

Publications and source records attributed to A Henger.

8 recordsLinked to original sources

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

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

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

Catecholamines modulate podocyte function.

The aim of this study was to investigate the influence of adrenoceptor agonists on the intracellular calcium activity ([Ca2+]i), membrane voltage (Vm), and ion conductances (Gm) in differentiated mouse podocytes. [Ca2+]i was measured by the Fura-2 fluorescence method in single podocytes. Noradrenaline and the alpha 1-adrenoceptor agonist phenylephrine induced a reversible and concentration-dependent biphasic increase of [Ca2+]i in podocytes (EC50 approximately 0.1 microM for peak and plateau), whereas the alpha 2-adrenoceptor agonist UK 14.304 did not influence [Ca2+]i. The [Ca2+]i response induced by noradrenaline was completely inhibited by the alpha 1-adrenoceptor antagonist prazosin (10 nM). In a solution with a high extracellular K+ (72.5 mM), [Ca2+]i was unchanged and the [Ca2+]i increase induced by noradrenaline was not inhibited by the L-type Ca2+ channel blocker nicardipine (1 microM). Vm and Gm were examined with the patch-clamp technique in the slow whole-cell configuration. Isoproterenol, phenylephrine, and noradrenaline depolarized podocytes and increased Gm. The order of potency for the adrenoceptor agonists was isoproterenol (EC50 approximately 1 nM) > noradrenaline (EC50 approximately 0.3 microM) > phenylephrine (EC50 approximately 0.5 microM). The beta 2-adrenoceptor antagonist ICI 118.551 (5 to 100 nM) inhibited the effect of isoproterenol on Vm. Stimulation of adenylate cyclase by forskolin mimicked the effect of isoproterenol on Vm and Gm (EC50 approximately 40 nM). Isoproterenol induced a time- and concentration-dependent increase of cAMP in podocytes. The effect of isoproterenol was unchanged in the absence of Na+ or in an extracellular solution with a reduced Ca2+ concentration, whereas it was significantly increased in an extracellular solution with a reduced Cl- concentration (from 145 to 32 mM). The data indicate that adrenoceptor agonists regulate podocyte function: They increase [Ca2+]i via an alpha 1-adrenoceptor and induce a depolarization via a beta 2-adrenoceptor. The depolarization is probably due to an opening of a cAMP-dependent Cl- conductance.

Adrenergic alpha-Agonists↗

PubMed1997

Angiotensin II depolarizes podocytes in the intact glomerulus of the Rat.

The aim of this study was to examine the effects of angiotensin II (Ang II) on cellular functions of rat podocytes (pod) in the intact freshly isolated glomerulus and in culture. Membrane voltage (Vm) and ion currents of pod were examined with the patch clamp technique in fast whole cell and whole cell nystatin configuration. Vm of pod was -38+/-1 mV (n = 86). Ang II led to a concentration-dependent depolarization of pod with an ED50 of 10(-8) mol/liter. In the presence of Ang II (10(-7) mol/liter, n = 20), pod depolarized by 7+/-1 mV. In an extracellular solution with a reduced Cl- concentration of 32 mmol/liter, the effect of Ang II on Vm was significantly increased to 14+/-4 mV (n = 8). The depolarization induced by Ang II was neither inhibited in an extracellular Na+-free solution nor in a solution with a reduced extracellular Ca2+ (down to 1 micromol/liter). Like Ang II, the calcium ionophore A23187 (10(-5) mol/liter, n = 9) depolarized pod by 10+/-2 mV, whereas forskolin (10(-5) mol/liter), 8-(4-chlorophenylthio)-cAMP and N2,2'-o-dibutyryl-cGMP (both 5 x 10(-4) mol/liter) did not alter Vm of pod. The angiotensin 1 receptor antagonist losartan (10(-7) mol/liter) completely inhibited the Ang II-induced (10(-7) mol/liter) depolarization (n = 5). Like pod in the glomerulus, pod in short term culture depolarized in response to Ang II (10(-8) mol/liter, n = 5). Our results suggest that Ang II depolarizes podocytes directly by opening a Cl- conductance. The activation of this ion conductance is mediated by an AT1 receptor and may be regulated by the intracellular Ca2+ activity.

Angiotensin II↗

PubMed1997

Agonist-induced activation of a non-selective ion current in glomerular endothelial cells.

The control of intracellular calcium activity ([Ca2+]i) and membrane voltage (Vm) play an important role in regulating functions of glomerular endothelial cells (GEC). We investigated the effect of extracellular ATP on the intracellular [Ca2+]i, Vm and ion conductances in GEC. ATP (100 mumol/liter) induced a rapid increase of [Ca2+]i in GEC from 20 +/- 6 to 442 +/- 84 nmol/liter, which was followed by a sustained Ca2+ plateau of 112 +/- 29 nmol/liter. In a bath solution with a low extracellular Ca2+ concentration the ATP-induced [Ca2+]i peak was still present, but the [Ca2+]i plateau was completely prevented. In 186 experiments with the patch clamp technique the addition of ATP (1 to 100 mumol/liter) to GEC induced a transient small hyperpolarization, which was followed by a depolarization. During the ATP-induced depolarization an increase of the whole cell conductance was found. The Ca2+ ionophore A23187 (10 mumol/liter) mimicked the effect of ATP on Vm. Reduction of the extracellular Ca2+ to 1 mumol/liter itself depolarized GEC reversibly from -88 +/- 2 to -60 +/- 12 mV and increased the ATP-induced depolarization to -18 +/- 3 mV. In the absence of Na+ in the bathing solution (replacement by NMDG+) ATP induced only an attenuated depolarization and no inward current was activated. Flufenamate (100 mumol/liter), a blocker of non-selective ion channels inhibited the ATP-induced depolarization of Vm significantly by 58 +/- 13%, whereas nicardipine (10 mumol/liter) or amiloride (10 mumol/liter) had no effect. Our data indicate that the resting Vm of GEC cells is almost completely dominated by K+ conductances and that ATP activates a Ca2+ dependent non-selective ion conductance in GEC.

Adenosine Triphosphate↗

PubMed1997

Angiotensin II increases the cytosolic calcium activity in rat podocytes in culture.

In the glomerulus, angiotensin II (Ang II) reduces the ultrafiltration coefficient and enhances the filtration of macromolecules. During glomerular injury, inhibition of the renin-angiotensin system by angiotensin-converting-enzyme inhibitors reduces proteinuria and retards the progression to end-stage renal insufficiency. The mechanisms by which Ang II modulates glomerular function are still a matter of investigation. To study whether Ang II may regulate the cytosolic calcium activity ([Ca2+]i) in podocytes, these cells were propagated in short-term culture and the effect of Ang II was examined with the Fura-2 microfluorescence technique in single podocytes. The cellular identity of cultured podocytes was proven by the expression of WT-1 and pp44, specific antibodies against podocytes in vivo. Ang II led to a concentration-dependent, reversible and slow increase of [Ca2+]i with an EC50 of 3 nmol/liter Ang II (N = 229). Ten nmol/liter Ang II increased [Ca2+]i from 41 +/- 9 to 260 +/- 34 nmol/liter (N = 210). In a solution with an extracellular reduced Ca2+ concentration of 10 micromol/liter, Ang II-mediated [Ca2+]i increase was significantly reduced by 60 +/- 20% (N = 12), indicating that the [Ca2+]i increase was due to a Ca2+ influx from the extracellular space and a release of Ca2+ from intracellular stores. Flufenamate, an inhibitor of non-selective ion channels, significantly inhibited Ang II-mediated increase of [Ca2+]i (IC50 = 20 micromol/liter, N = 29), whereas the L-type Ca2+ channel blocker nicardipine even in high concentrations of > 1 micromol/liter had only a small inhibitory effect. The AT1 receptor antagonist losartan inhibited Ang II-mediated [Ca2+]i increase with an IC50 of about 0.3 nmol/liter (N = 35). The data suggest that Ang II increases [Ca2+]i in podocytes by an influx of Ca2+ through non-selective channels and by a release of Ca2+ from intracellular stores. The effect of Ang II is mediated via an AT1 receptor.

Angiotensin II↗

PubMed1996

Extracellular ATP regulates glomerular endothelial cell function.

1. Glomerular endothelial cells form the inner part of the filtration barrier and are involved in pathophysiological processes in the glomerulum. New techniques for culturing glomerular endothelial cells have been established recently. The effect of extracellular ATP on membrane voltage and intracellular calcium activity was examined in bovine glomerular endothelial cells (GEC) in culture. 2. Membrane voltage was measured with the patch clamp technique in the fast whole cell configuration. GEC possess a stable membrane voltage of -88 mV. ATP induced a small transient hyperpolarization, which was followed by a depolarization. The ATP-induced depolarization was significantly inhibited by flufenamate, a blocker of non-selective ion channels. 3. The intracellular calcium activity [Ca2+]i was measured in single cells with the fura-2 technique. ATP stimulated an increase of [Ca2+]i. The increase of [Ca2+]i was biphasic with an initial peak followed by a sustained plateau. The [Ca2+]i peak was still present in an extracellular Ca(2+)-free solution, whereas the plateau was inhibited. 4. The order of potency of different purine nucleotides in stimulating [Ca2+]i and inositol formation was UTP = ATP > ATP-gamma-S > 2-methylthio ATP > [alpha,beta-CH2]ATP. 5. The data indicate that ATP regulates membrane voltage and [Ca2+]i in glomerular endothelial cells by a P2y2 receptor.

Adenosine Triphosphate↗