A Swelling-Activated Chloride Current in Microglial Cells is Suppressed by Epac and Facilitated by PKA - Impact on Phagocytosis

Cell Physiol Biochem. 2019;52(5):951-969. doi: 10.33594/000000066.

Abstract

Background/aims: Volume-regulated anion channels (VRACs) are of particular importance in regulating the cell volume (CV) and give rise to the swelling-activated Cl- current (ICl,swell), a main component driving global regulatory volume decrease (RVD) during cell swelling. Because ICl,swell affects numerous CV-regulated processes like migration, we assume that its role is also indispensable for phagocytosis which requires local cell swelling. Noradrenaline (NA) modulates phagocytosis in macrophages and microglial cells, macrophage-related cells in the central nervous system. Therefore we evaluated whether NA modulates ICl,swell and phagocytosis in microglia.

Methods: Experiments were performed in murine microglial BV-2 and primary mouse microglial cells. Patch clamp experiments were performed in BV-2 cells using the amphotericin-perforated method to minimize cytosolic disturbances. Phagocytosis was quantified by scanning electron microscopy.

Results: Following activation of ICl,swell by a hypotonic bath solution, noradrenaline, as well as the β-adrenergic agonist isoproterenol, evoked a transient decrease of ICl,swell. Repeated application of adrenergic agonists caused a decline of this electrical response. Application of the agonist of exchange protein directly activated by cAMP (Epac), 8-pCPT-2-O-Me-cAMP, or the protein kinase A inhibitor H89 caused a persistent suppression of ICl,swell. When isoproterenol was added concomitantly with the hypotonic saline, ICl,swell developed more rapidly compared to control conditions. Uptake of IgG-coated beads was suppressed by NA or H89 when quantified after 15 min of exposure.

Conclusion: The activation of β-adrenergic receptors in microglial cells triggers a cAMP-Epac-dependent and a cAMP-PKA-dependent cascade which affects phagocytosis via modulation of the swelling-activated Cl- current ICl,swell.

Keywords: Adrenoceptors; BV-2 cells; Cell volume regulation; Epac; ICl,swell; Microglia; Noradrenaline; PKA; Phagocytosis; VRAC; cAMP.

MeSH terms

  • Animals
  • Cell Size
  • Cells, Cultured
  • Chlorides / metabolism*
  • Cyclic AMP / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Ion Transport
  • Mice
  • Microglia / metabolism*
  • Microglia / pathology
  • Phagocytosis*
  • Second Messenger Systems*

Substances

  • Chlorides
  • Epac protein, mouse
  • Guanine Nucleotide Exchange Factors
  • Cyclic AMP
  • Cyclic AMP-Dependent Protein Kinases