Modulation of Ca2+ Influx in Leech Retzius Neurons II. Effect of Extracellular Ca2+

Modulation of Ca2+ Influx in Leech Retzius Neurons II. Effect of Extracellular Ca2+ We investigated the cytosolic free calcium concentration ([Ca2+]i) of leech Retzius neurons in situ while varying the extracellular Ca2+ concentration via the bathing solution ([Ca2+]B). Changing [Ca2+]B had only an effect on [Ca2+]i if the cells were depolarized by raising the extracellular K+ concentration. Surprisingly, raising [Ca2+]B from 2 to 10 mm caused a decrease in [Ca2+]i, and an increase was evoked by reducing [Ca2+]B to 0.1 mm. These changes were not due to shifts in membrane potential. At low [Ca2+]B moderate membrane depolarizations were sufficient to evoke a [Ca2+]i increase, while progressively larger depolarizations were necessary at higher [Ca2+]B. The changes in the relationship between [Ca2+]i and membrane potential upon varying [Ca2+]B could be reversed by changing extracellular pH. We conclude that [Ca2+]B affects [Ca2+]i by modulating Ca2+ influx through voltage-dependent Ca2+ channels via the electrochemical Ca2+ gradient and the surface potential at the extracellular side of the plasma membrane. These two parameters are affected in a counteracting way: Raising the extracellular Ca2+ concentration enhances the electrochemical Ca2+ gradient and hence Ca2+ influx, but it attenuates Ca2+ channel activity by shifting the extracellular surface potential to the positive direction, and vice versa. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

Modulation of Ca2+ Influx in Leech Retzius Neurons II. Effect of Extracellular Ca2+

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Publisher
Springer Journals
Copyright
Copyright © Inc. by 2001 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-001-0070-9
Publisher site
See Article on Publisher Site

Abstract

We investigated the cytosolic free calcium concentration ([Ca2+]i) of leech Retzius neurons in situ while varying the extracellular Ca2+ concentration via the bathing solution ([Ca2+]B). Changing [Ca2+]B had only an effect on [Ca2+]i if the cells were depolarized by raising the extracellular K+ concentration. Surprisingly, raising [Ca2+]B from 2 to 10 mm caused a decrease in [Ca2+]i, and an increase was evoked by reducing [Ca2+]B to 0.1 mm. These changes were not due to shifts in membrane potential. At low [Ca2+]B moderate membrane depolarizations were sufficient to evoke a [Ca2+]i increase, while progressively larger depolarizations were necessary at higher [Ca2+]B. The changes in the relationship between [Ca2+]i and membrane potential upon varying [Ca2+]B could be reversed by changing extracellular pH. We conclude that [Ca2+]B affects [Ca2+]i by modulating Ca2+ influx through voltage-dependent Ca2+ channels via the electrochemical Ca2+ gradient and the surface potential at the extracellular side of the plasma membrane. These two parameters are affected in a counteracting way: Raising the extracellular Ca2+ concentration enhances the electrochemical Ca2+ gradient and hence Ca2+ influx, but it attenuates Ca2+ channel activity by shifting the extracellular surface potential to the positive direction, and vice versa.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Nov 1, 2001

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