Selective activation of KCa3.1 and CRAC channels by P2Y2 receptors promotes Ca(2+) signaling, store refilling and migration of rat microglial cells

PLoS One. 2013 Apr 19;8(4):e62345. doi: 10.1371/journal.pone.0062345. Print 2013.

Abstract

Microglial activation involves Ca(2+) signaling, and numerous receptors can evoke elevation of intracellular Ca(2+). ATP released from damaged brain cells can activate ionotropic and metabotropic purinergic receptors, and act as a chemoattractant for microglia. Metabotropic P2Y receptors evoke a Ca(2+) rise through release from intracellular Ca(2+) stores and store-operated Ca(2+) entry, and some have been implicated in microglial migration. This Ca(2+) rise is expected to activate small-conductance Ca(2+)-dependent K(+) (SK) channels, if present. We previously found that SK3 (KCa2.3) and KCa3.1 (SK4/IK1) are expressed in rat microglia and contribute to LPS-mediated activation and neurotoxicity. However, neither current has been studied by elevating Ca(2+) during whole-cell recordings. We hypothesized that, rather than responding only to Ca(2+), each channel type might be coupled to different receptor-mediated pathways. Here, our objective was to determine whether the channels are differentially activated by P2Y receptors, and, if so, whether they play differing roles. We used primary rat microglia and a rat microglial cell line (MLS-9) in which riluzole robustly activates both SK3 and KCa3.1 currents. Using electrophysiological, Ca(2+) imaging and pharmacological approaches, we show selective functional coupling of KCa3.1 to UTP-mediated P2Y2 receptor activation. KCa3.1 current is activated by Ca(2+) entry through Ca(2+)-release-activated Ca(2+) (CRAC/Orai1) channels, and both CRAC/Orai1 and KCa3.1 channels facilitate refilling of Ca(2+) stores. The Ca(2+) dependence of KCa3.1 channel activation was skewed to abnormally high concentrations, and we present evidence for a close physical association of the two channel types. Finally, migration of primary rat microglia was stimulated by UTP and inhibited by blocking either KCa3.1 or CRAC/Orai1 channels. This is the first report of selective coupling of one type of SK channel to purinergic stimulation of microglia, transactivation of KCa3.1 channels by CRAC/Orai1, and coordinated roles for both channels in store refilling, Ca(2+) signaling and microglial migration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium Channels / metabolism*
  • Calcium Signaling* / drug effects
  • Cell Line
  • Cell Movement* / drug effects
  • Intermediate-Conductance Calcium-Activated Potassium Channels / metabolism*
  • Intracellular Space / drug effects
  • Intracellular Space / metabolism
  • Ion Channel Gating* / drug effects
  • Microglia / cytology*
  • Microglia / drug effects
  • Microglia / metabolism
  • ORAI1 Protein
  • Rats
  • Receptors, Purinergic P2Y2 / metabolism*
  • Uridine Triphosphate / pharmacology

Substances

  • Calcium Channels
  • Intermediate-Conductance Calcium-Activated Potassium Channels
  • Kcnn4 protein, rat
  • ORAI1 Protein
  • Orai1 protein, rat
  • Receptors, Purinergic P2Y2
  • Uridine Triphosphate

Grant support

This research was supported by an operating grant to LCS from the Heart and Stroke Foundation, Ontario chapter (HSFO, #T6766), and graduate scholarships to RF from HSFO (Ontario Graduate Scholarship in Science and Technology) and the Natural Sciences and Engineering Research Council (NSERC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.