Evidence for the uptake of neuronally derived choline by glial cells in the leech central nervous system.

Abstract

SUMMARY1. With ion-sensitive microelectrodes based on the Corning exchanger 477317, the accumulation of an unidentified interfering substance was monitored in leech neuropile glial cells but not in neurones after a 10-fold increase in extracellular K+ concentration. Evidence is presented which shows that this substance may be choline.2. The accumulation of interfering ions was not observed in Ca2+-free saline and was substantially reduced in the presence of eserine (a blocker of acetylcholinesterase).3. In neuropile (and also packet) glial cells, extracellularly applied choline (10-4 M) caused a steady increase in ion signal. This increase was not affected by removal of extracellular calcium, by hemicholinium-3 (a blocker of high-affinity choline uptake) or eserine. Shortly after the removal of choline from the saline the increase in ion signal stopped and the ion signal then decreased slowly to its original level.4. Extracellular acetylcholine (10-4 M) caused a similar increase in intracellular ion signal of neuropile glial cells to that caused by choline. This increase was blocked by eserine.5. Extracellular choline caused a comparatively small increase in ion signal of Retzius neurones which was blocked by hemicholinium-3. In pressure neurones, choline or hemicholinium-3 had no effect on intracellular ion signal.6. Autoradiographic analysis of [3H]choline uptake showed that most of the choline was taken up by glial cells in a time-and dose-dependent manner. Small but significant amounts of choline were taken up by neurones and connective tissue.7. It is concluded that the neuropile and packet glial cells possess an effective choline uptake system which is activated by exogenous choline but also by choline that stems from enzymatic inactivation of acetylcholine released by neurones.

Sodium-sensitive, calcium-independent potassium conductance in the leech giant glial cell

“…When Na + was replaced by choline an additional transient inward current could be observed (Fig. 1B), which was probably due to cholinergic receptor activation [3] and/or an uptake of choline into these cells [38]. The persisting components of current response and conductance increase, however, were similar to that obtained with NMDG and TRIS as Na + substitutes.…”

Stratification of astrocytes in healthy and diseased brain

“…Packet glia regulate K + homeostasis around neuronal somata , whereas giant glial cells control ion homeostasis in the neuropil, being particularly important for regulation of pH (by plasmalemmal Na + ‐ co‐transporter, Na + ‐H + and Cl – ‐ exchangers). Furthermore giant glial cells remove extracellular glutamate and choline through dedicated Na + ‐dependent plasmalemmal transporters .…”

Glial Swelling in Ischemia: A Hypothesis

“…Mi croelectrodes were used for impalements to measure the intracellular choline concentration. The idea was that the electrodes, if mainly sensitive to choline, can be used to estimate choline loading, its dilution by swelling [31] and the lime course of the swelling. We found previously that choline is taken up by astrocytes and metabolized very slowly.…”