Polycations induce calcium signaling in glomerular podocytes

Kidney Int. 1999 Nov;56(5):1700-9. doi: 10.1046/j.1523-1755.1999.00729.x.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / analogs & derivatives
  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / pharmacology
  • 3T3 Cells
  • Animals
  • Benzoquinones
  • Calcium Signaling*
  • Cells, Cultured
  • DEAE-Dextran / pharmacology
  • Heparin / pharmacology
  • Kidney Glomerulus / metabolism*
  • Lactams, Macrocyclic
  • Mice
  • Muramidase / pharmacology
  • Oxazoles / pharmacology
  • Protamines / pharmacology
  • Quinones / pharmacology
  • Rifabutin / analogs & derivatives
  • Staurosporine / pharmacology
  • Thapsigargin / pharmacology

Substances

  • Benzoquinones
  • Lactams, Macrocyclic
  • Oxazoles
  • Protamines
  • Quinones
  • Rifabutin
  • KN 62
  • Thapsigargin
  • herbimycin
  • calyculin A
  • 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine
  • Heparin
  • DEAE-Dextran
  • Muramidase
  • Staurosporine