Relations between slow extracellular potential changes, glial potassium buffering, and electrolyte and cellular volume changes during neuronal hyperactivity in cat brain

Abstract

The aim of this investigation is to estimate the contribution of spatial glial K+ buffer currents to extracellular K+ homeostasis during enhanced neuronal activity. Neuronal hyperactivity was induced by electrical stimulation of the cortical surface or the ventrobasal thalamic nuclei of cats (5-50 Hz, 0.1-0.2 ms, two to three times threshold stimulation intensity, 5-20 s). The accompanying slow field potential changes were recorded simultaneously across the grey matter with vertical assemblies of eight micropipettes glued 300 microns apart. Using the Poisson equation, the amplitudes of the underlying current sources and sinks were calculated. The current source densities depended on the depth of recording, frequency, strength, and duration of the stimulation. Current sinks, corresponding to a removal of 0.1-0.5 mmoles of monovalent cations per liter of brain tissue and second from the extracellular space, were observed in middle cortical layers, whereas sources appeared at superficial and deeper sites. These sinks and sources might represent K+ moved across glial membranes by spatial buffer currents. The consequences of glial buffer currents of this magnitude were investigated with model calculations. It turned out that measurements of electrolyte and volume changes of the extracellular space (Dietzel et al. Exp. Brain Res. 40:432-439, 1980; Exp. Brain Res. 46:73-84, 1982) could only partially be explained by spatial buffer currents of this magnitude. Comparison of the calculated values with intracellular measurements in neurons and glial cells (Coles et al. Ann. N.Y. Acad. Sci. 481:303-317, 1986; Ballanyi et al. J. Physiol. 382:159-174, 1987) suggests that spatial buffering combines with an approximately equimolar KCl transport and, depending on the preparation, also K+/Na+-exchange across glial membranes.

Infraslow oscillations modulate excitability and interictal epileptic activity in the human cortex during sleep

“…In addition, multiple lines of evidence have pointed to a generation of large-scale, slow electric signals by nonneuronal sources, such as the glial cells (17,(36)(37)(38) and the blood-brain barrier (see refs. 14 and 39 and references therein).…”

Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

“…Spatial buffering inevitably generates slow extracellular field potentials (e.g. Gardner-Medwin, Coles & Tsacopoulos, 1981;Dietzel, Heinemann & Lux, 1989). Slow field potentials can be seen in Fig.…”

Swelling-activated chloride channels in leech Retzius neurons

“…Increases in the extracellular K + concentration up to 10·mmol·l -1 were observed after high neuronal activity in the leech and in other preparations (Baylor and Nicholls, 1969;Dietzel et al, 1989), up to ) had little effect on the cell shrinkage under hypertonic conditions (+85·mmol·l -1 NaCl) but caused an increased swelling under hypotonic conditions (-59·mmol·l -1 NaCl; 5·min each). The effects were abolished in the presence of the tubulin polymerization enhancer paclitaxel (30·nmol·l -1 ).…”