Mechanisms for the Passive Regulation of Extracellular K+ in the Central Nervous System: The Implications of Invertebrate Studies
Homeostasis of the brain extracellular K concentration is a necessary prerequisite for neuronal functioning and synaptic integration3,7. There is considerable evidence for such regulation in vertebrate brain, and when the interstitial K concentration is maintained constant in the face of chronically altered K levels in blood, an active, energy-dependent mechanism is suggested7. However, it is not known to what extent the brain can maintain a degree of internal homeostasis by purely passive ‘K buffering’ systems. In this paper we shall examine the evidence for active and passive regulation of K in the brain microenvironment and discuss some results from a crustacean preparation which indicate that passive K buffering may occur. Possible involvement of glia, and alternative mechanisms, will be discussed. As astrocytes have been suggested as a major site for K buffering in the vertebrate brain, evidence for a homeostatic function of astrocytes will be considered.
KeywordsEthacrynic Acid Extracellular Potassium Passive Mechanism Vertebrate Brain Glial Membrane
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