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

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.

Section: Animals and Preparationmentioning

confidence: 99%

“…In a comparative study, Schlue & Wuttke (1983) found marked differences in intracellular K+ activity (a) (Schlue & Wuttke, 1983).…”

Section: Introductionmentioning

confidence: 99%

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

Wuttke

Pentreath

1990

“…We have also measured the pHi of neurones in the same preparation and have compared the steady-state pHi and the regulation of pHi under various conditions in glial cells and neurones. The nervous system of the leech has appeared particularly suitable for this kind of study for the following reasons: (1) individual neurones and glial cells can be identified and penetrated by micro-electrodes (Nicholls & Kuffler, 1964; Baylor & Nicholls, 1969;Jansen & Nicholls, 1973; Schlue, Schliep & Walz, 1980;Walz & Schlue, 1982); and (2) several types of ion-sensitive micro-electrodes have been successfully used for extra-and intracellular recording of ions in the leech central nervous system (Schlue & Deitmer, 1980;Deitmer & Schlue, 1981Schlue & Wuttke, 1983;Schlue & Thomas, 1985). Our results reveal both similarities and differences concerning the maintenance of pHi in the two types of brain cells.…”

Section: Introductionmentioning

confidence: 99%

The regulation of intracellular pH by identified glial cells and neurones in the central nervous system of the leech.

Deitmer

Schlue

1987

135

SUMMARY1. Double-barrelled, neutral-carrier pH-sensitive micro-electrodes were used to measure the intracellular pH (pHi) and the pHi regulation of neuropile glial (n.g.) cells and of identified neurones of the leech Hirudo medicinalis.2. The distribution of H+ in the n.g. cells and in the neurones was found not to be in electrical equilibrium. The mean pHi ofthe n.g. cells was 6-87 + 0 13 (mean + S.D.of mean here and for all following data n = 27) in HEPES-buffered leech saline (pHo = 7 4) and 7418 + 0-19 (n = 13) in 2 % C02-11 mM-HC03--saline. The mean pHi was 7'28+0-1 (n = 20) in Retzius neurones and 7-32+0415 (n = 12) in noxious neurones in HEPES-buffered leech saline, and 7-20+0415 (n = 10) and 7-27 +016 (n = 6) in 2 % C02-1 1 mM-HC03--buffered saline in these two types of neurones, respectively.3. The cytoplasmic buffering power, as calculated by the change in pHi following the change from 2 % C02-11 mM-HC03-to 5 % C02-22 mM-HCO.-in the leech saline, was 20-30 mM/pH unit in the n.g. cells and between 12 and 33 mM/pH unit in the neurones.4. The recovery of pHi in n.g. cells from an experimentally induced acidification (addition and removal of 20 mm-NH4Cl) was dependent on the presence of external Na+. Independent of the buffer system used, pHi recovery was inhibited when external Na+ was exchanged by N-methyl-D-glucamine. Amiloride (2-3 mM) reduced the rate of pHi recovery by about 50 % in these n.g. cells.5. In CO2-HCO3--free saline, or in the presence of the anion exchange blocker 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulphonic acid (SITS, 0 5 mM), pHi recovery from an acid load was often slowed by up to 50 % in n.g. cells. This suggests that there is a significant contribution of a HC03--dependent membrane transport to pHi regulation in n.g. cells.6. When a HEPES-buffered saline was exchanged by a 2 % C02-11 mM-HCO3-buffered saline, the pHi of n.g. cells increased by 0-31 pH units. This alkaline shift was reversible upon removal of the CO2-HC03-and was absent in the Na+-free saline. It was not inhibited by 1 mM-furosemide or by 0 5 mM-SITS. Successive addition of first Na+ and then CO2-HCO3-to an Na+-free HEPES-buffered saline produced two separate phases of intracellular alkalization, suggesting two different pHi regulation transport systems.J. W. DEITMER AND W.-R. SCHLUE 7. In sensory and Retzius neurones pHi recovery from acidification was also dependent on external Na+, both in the presence and in the absence of CO2-HC03-.The rate of pHi recovery was reversibly reduced by 2 mM-amiloride by up to 90 % in these neurones.8. In conclusion, bicarbonate buffer affects n.g. cell pHi differently from the way in which it affects neuronal pHi. The regulation of pHi depends on the presence of external Na+ in both n.g. cells and neurones. The experiments suggest the presence of an Na+-H+ exchange and a SITS-sensitive HCO3--and Na+-dependent acid extrusion mechanism across n.g. (and nerve cell) membranes and another, SITSinsensitive HC03-and Na+-dependent transport system only in n.g. cells.

“…Kimelberg, 1981 Kettenmann, 1987;Walz, 1987) neuropile glial cells accumulate K+ at elevated [K+]. (Schlue & Wuttke, 1983 (Sjodin & Ortiz, 1975). A similar mechanism might operate in the neuropile glial cells.…”

Section: Chloride Distributionmentioning

confidence: 99%

Intracellular chloride activity in glial cells of the leech central nervous system.

Ballanyi

Schlue

1990