Potassium activity in leech neuropile glial cells changes with external potassium concentration

The effect of the external K + concentration on the intracellular K + activity of neuropile glial cells and of sensory neurons in the central nervous system of the leech ( Hirudo medicinalis L.) was determined directly with double-barreled ion-sensitive microelectrodes. As the external K + concentration was raised, the intracellular K + activity of the neuropile glial cells increased considerably, and was accompanied by the uptake and/or intracellular synthesis of an, as yet, unidentified substance. In contrast, the intracellular K + activity of sensory neurons was unchanged when the external K + concentration was increased. These neurons appeared not to accumulate a second substance.