K+‐Permeability of the Blood‐Brain Barrier, Investigated by Aid of a K+‐Sensitive Microelectrode

Abstract

The K+-permeability of the blood-brain barrier at the capillary level was estimated from determinations of brain extracellular K+-concentration in response to an isotonic bolus containing KC1 injected into the carotid artery. A very low permeability appeared from the fact that the extracellular K+-concentration—measured by aid of K+-sensitive microelectrodes—remained unchanged during the passage of the bolus. An upper limit for the blood-brain barrier K.+-permeability in the rat was estimated to be 2.8 7times; 10^-7 cm · s^-1.