Astrocytes in the retrotrapezoid nucleus sense H+ by inhibition of a Kir4.1-Kir5.1-like current and may contribute to chemoreception by a purinergic mechanism

J Neurophysiol. 2010 Dec;104(6):3042-52. doi: 10.1152/jn.00544.2010. Epub 2010 Oct 6.

Abstract

Central chemoreception is the mechanism by which CO(2)/pH sensors regulate breathing in response to tissue pH changes. There is compelling evidence that pH-sensitive neurons in the retrotrapezoid nucleus (RTN) are important chemoreceptors. Evidence also indicates that CO(2)/H(+)-evoked adenosine 5'-triphosphate (ATP) release in the RTN, from pH-sensitive astrocytes, contributes to chemoreception. However, mechanism(s) by which RTN astrocytes sense pH is unknown and their contribution to chemoreception remains controversial. Here, we use the brain slice preparation and a combination of patch-clamp electrophysiology and immunohistochemistry to confirm that RTN astrocytes are pH sensitive and to determine mechanisms by which they sense pH. We show that pH-sensitive RTN glia are immunoreactive for aldehyde dehydrogenase 1L1, a marker of astrocytes. In HEPES buffer the pH-sensitive current expressed by RTN astrocytes reversed near E(K(+)) (the equilibrium potential for K(+)) and was inhibited by Ba(2+) and desipramine (blocker of Kir4.1-containing channels), characteristics most consistent with heteromeric Kir4.1-Kir5.1 channels. In bicarbonate buffer, the sodium/bicarbonate cotransporter also contributed to the CO(2)/H(+)-sensitive current in RTN astrocytes. To test the hypothesis that RTN astrocytes contribute to chemoreception by a purinergic mechanism, we used fluorocitrate to selectively depolarize astrocytes while measuring neuronal activity. We found that fluorocitrate increased baseline activity and pH sensitivity of RTN neurons by a P2-receptor-dependent mechanism, suggesting that astrocytes may release ATP to activate RTN chemoreceptors. We also found in bicarbonate but not HEPES buffer that P2-receptor antagonists decreased CO(2) sensitivity of RTN neurons. We conclude that RTN astrocytes sense CO(2)/H(+) in part by inhibition of a Kir4.1-Kir5.1-like current and may provide an excitatory purinergic drive to pH-sensitive neurons.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / physiology
  • Animals
  • Astrocytes / drug effects
  • Astrocytes / physiology*
  • Barium / pharmacology
  • Carbon Dioxide / pharmacology
  • Chemoreceptor Cells / drug effects
  • Chemoreceptor Cells / physiology*
  • Citrates / pharmacology
  • Desipramine / pharmacology
  • Hydrogen-Ion Concentration*
  • Neurons / drug effects
  • Neurons / physiology
  • Patch-Clamp Techniques
  • Potassium Channels, Inwardly Rectifying / antagonists & inhibitors
  • Potassium Channels, Inwardly Rectifying / physiology*
  • Purinergic P2 Receptor Antagonists / pharmacology
  • Pyridoxal Phosphate / analogs & derivatives
  • Pyridoxal Phosphate / pharmacology
  • Rats
  • Receptors, Purinergic P2 / physiology*
  • Respiratory Center / physiology*
  • Sodium-Bicarbonate Symporters / physiology
  • Suramin / pharmacology

Substances

  • Citrates
  • Kcnj10 (channel)
  • Kir5.1 channel
  • Potassium Channels, Inwardly Rectifying
  • Purinergic P2 Receptor Antagonists
  • Receptors, Purinergic P2
  • Sodium-Bicarbonate Symporters
  • Carbon Dioxide
  • pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid
  • Barium
  • fluorocitrate
  • Pyridoxal Phosphate
  • Suramin
  • Adenosine Triphosphate
  • Desipramine