Glial cells and extracellular potassium: their relationship in mammalian cortex.
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.
D000818:Animals; D002415:Cats; D002540:Cerebral Cortex / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D008564:Membrane Potentials; D009457:Neuroglia / Q000378:metabolism*; D010400:Penicillin G; D011188:Potassium / Q000378:metabolism*; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism*
D010400:Penicillin G; D011188:Potassium