Premium
Analysis of K + accumulation reveals privileged extracellular region in the vicinity of glial cells in situ
Author(s) -
Chvátal Alexandr,
Anděrová Miroslava,
Syková Eva
Publication year - 2004
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.20284
Subject(s) - depolarization , membrane potential , biophysics , astrocyte , extracellular , oligodendrocyte , spinal cord , chemistry , neuroglia , neuroscience , anatomy , biology , central nervous system , myelin , biochemistry
Astrocytes and oligodendrocytes in rat and mouse spinal cord slices, characterized by passive membrane currents during de‐ and hyperpolarizing stimulation pulses, express a high resting K + conductance. In contrast to the case for astrocytes, a depolarizing prepulse in oligodendrocytes produces a significant shift of reversal potential (V rev ) to positive values, arising from the larger accumulation of K + in the vicinity of the oligodendrocyte membrane. As a result, oligodendrocytes express large tail currents (I tail ) after a depolarizing prepulse due to the shift of K + into the cell. In the present study, we used a mathematical model to calculate the volume of the extracellular space (ECS) in the vicinity of astrocytes and oligodendrocytes (ESV v ), defined as the volume available for K + accumulation during membrane depolarization. A mathematical analysis of membrane currents revealed no differences between glial cells from mouse (n = 59) or rat (n = 60) spinal cord slices. We found that the V rev of a cell after a depolarizing pulse increases with increasing I tail , expressed as the ratio of the integral inward current (Q in ) after the depolarizing pulse to the total integral outward current (Q out ) during the pulse. In astrocytes with small I tail and V rev ranging from −50 to −70 mV, the Q in was only 3–19% of Q out , whereas, in oligodendrocytes with large I tail and V rev between −20 and 0 mV, Q in /Q out was 30–75%. On the other hand, ESV v decreased with increasing values of V rev . In astrocytes, ESV v ranged from 2 to 50 μm 3 , and, in oligodendrocytes, it ranged from 0.1 to 2.0 μm 3 . Cell swelling evoked by the application of hypotonic solution shifted V rev to more positive values by 17.2 ± 1.8 mV and was accompanied by a decrease in ESV v of 3.6 ± 1.3 μm 3 . Our mathematical analysis reveals a 10–100 times smaller region of the extracellular space available for K + accumulation during cell depolarization in the vicinity of oligodendrocytes than in the vicinity of astrocytes. The presence of such privileged regions around cells in the CNS may affect the accumulation and diffusion of other neuroactive substances and alter communication between cells in the CNS. © 2004 Wiley‐Liss, Inc.