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

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 (I), a main component driving global regulatory volume decrease (RVD) during cell swelling. Because I 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 I 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 I by a hypotonic bath solution, noradrenaline, as well as the β-adrenergic agonist isoproterenol, evoked a transient decrease of I. 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 I. When isoproterenol was added concomitantly with the hypotonic saline, I 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 I.