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.
Rüdiger
F
F
Division of Nephrology, Department of Medicine, University of Freiburg, Germany.
Greger
R
R
Nitschke
R
R
Henger
A
A
Mundel
P
P
Pavenstädt
H
H
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D016475:3T3 Cells; D000818:Animals; D016227:Benzoquinones; D020013:Calcium Signaling; D002478:Cells, Cultured; D003637:DEAE-Dextran / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000378:metabolism*; D047029:Lactams, Macrocyclic; D008387:Marine Toxins; D051379:Mice; D009113:Muramidase / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology; D011479:Protamines / Q000494:pharmacology; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D019311:Staurosporine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D008387:Marine Toxins; D010080:Oxazoles; D011479:Protamines; D011809:Quinones; D017828:Rifabutin; C063302:KN 62; D019284:Thapsigargin; C020754:herbimycin; C059041:calyculin A; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D006493:Heparin; D003637:DEAE-Dextran; D009113:Muramidase; D019311:Staurosporine