Glial cells and extracellular potassium: their relationship in mammalian cortex

Brain Res. 1976 Jun 11;109(2):311-22. doi: 10.1016/0006-8993(76)90532-1.

Abstract

Simultaneous recordings were made of glial cell potentials and the extracellular potassium concentration ([K+]O) in cat cortex in an attempt to provide more quantitative information about the sensitivity of mammalian neuroglia to changes in [K+]O. A penicillin epileptogenic focus served to generate both transient and sustained elevations in [K+]O, thus allowing measurement of glial membrane potential (Vm) at both resting and increased [K+]O levels many times during the same experiment. Resting Vm averaged--92.6 +/- 10.9 mV for 33 glial cells. With each surface interictal spike, glial cells exhibited slow depolarizations averaging 18.4 +/- 6.5 mV which mirrored rises in [K+]O in many respects. Several discrepancies were found, however, between transient and focal rises in [K+]O and the associated glial cell depolarizations which made it difficult to determine accurately the effect of changes in [K+]O on glial Vm. For example, the amplitude of the glial depolarization caused by a single interictal discharge showed no constant relationship to depth below the cortical surface in contrast to the consistent laminar profile recorded by the K+ electrode. Thus, large glial membrane depolarizations could be recorded at times when there was little or no increase in measured [K+]O. Agreement between changes in [K+]O and glial cell depolarizations was closer to that predicted by the Nernst equation during sustained elevations in [K+]O such as occurred during ictal episodes ('seizures'). These findings may be related in part to methodology as a consequence of the different spatial relationships which exist between glial membrane, K+-electrode tip and released K+. In addition, though, they may indicate the presence of a functional glial syncytium.

Publication types

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

MeSH terms

  • Animals
  • Cats
  • Cerebral Cortex / metabolism*
  • Extracellular Space / metabolism
  • Membrane Potentials*
  • Neuroglia / metabolism*
  • Penicillin G
  • Potassium / metabolism*
  • Seizures / chemically induced
  • Seizures / metabolism*

Substances

  • Penicillin G
  • Potassium