Biophysical and pharmacological characterization of inwardly rectifying K+ currents in rat spinal cord astrocytes

J Neurophysiol. 1995 Jan;73(1):333-46. doi: 10.1152/jn.1995.73.1.333.


1. Whole cell and cell-attached patch-clamp recordings were obtained from rat spinal cord astrocytes maintained in culture for 6-14 days. It was found that the resting conductance in these astrocytes is primarily due to inwardly rectifying K+ (Kir) channels. 2. Two types of astrocytic Kir channels were identified with single-channel conductances of approximately 28 and approximately 80 pS, respectively. Channels displayed some voltage dependence in their open probability, which was largest (0.8-0.9) near the K+ equilibrium potential (Ek) and decreased at more negative potentials. The resting potential closely followed Ek, so it can be assumed that Kir channels have a high open probability at the resting potential. 3. The conductance of inwardly rectifying K+ currents (Kir) depended strongly on [K+]o and was approximately proportional to the square-root of [K+]o. 4. Kir currents inactivated in a time- and voltage-dependent manner. The Na+ dependence of inactivation was studied with ion substitution experiments. Replacement of [Na+]o with choline or Li+ removed inactivation. This dependence of current inactivation on [Na+]o resembles the previously described block of Kir channels in other systems by [Na+]o. 5. Kir currents were also blocked in a dose-dependent manner by Cs+ (Kd = 189 microM at -140 mV), Ba2+ (Kd = 3.5 microM), and tetraethylammonium (TEA; 90% block at 10 mM) but were insensitive to 4-aminopyridine (4-AP; 5 mM). In the current-clamp mode, Ba2+ and TEA inhibition of Kir currents was associated with a marked depolarization, suggesting that Kir channel activity played a role in the establishment of the negative resting potential typical of astrocytes. 6. These biophysical features of astrocyte inwardly rectifying K+ channels are consistent with those properties required for their proposed involvement in [K+]o clearance: 1) high open probability at the resting potential, 2) increasing conductance with increasing [K+]o, and 3) rectification, e.g., channel closure, at positive potentials. It is proposed, therefore, that the dissipation of [K+]o following neuronal activity is mediated primarily by the activity of astrocytic Kir channels.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 4-Aminopyridine / pharmacology
  • Animals
  • Astrocytes / physiology*
  • Barium / pharmacology
  • Cesium / pharmacology
  • Dose-Response Relationship, Drug
  • Patch-Clamp Techniques
  • Potassium Channels / pharmacology*
  • Potassium Compounds / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Spinal Cord / physiology*


  • Potassium Channels
  • Potassium Compounds
  • Cesium
  • Barium
  • 4-Aminopyridine