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Intracellular Ca2+ regulation by the leech giant glial cell
1Abteilung fur Allgemeine Zoologie, FB Biologie, Universitat Kaiserslautern, Postfach 3049, D-67653 Kaiserslautern, Germany. wnett@rhrk.uni-kl.de
The Journal of Physiology
|April 4, 1998
Summary
The plasma membrane Ca2+-ATPase primarily maintains low intracellular calcium ([Ca2+]i) in leech glial cells. This ATPase also extrudes calcium after a load, with intracellular stores playing a minor role.
Area of Science:
- Neuroscience
- Cell Physiology
- Biochemistry
Background:
- Intracellular calcium concentration ([Ca2+]i) regulation is crucial for cell function.
- Glial cells play vital roles in the central nervous system.
- Understanding ion homeostasis in glial cells is essential.
Purpose of the Study:
- To investigate the mechanisms maintaining intracellular calcium and sodium concentrations in leech glial cells.
- To determine the role of the plasma membrane Ca2+-ATPase and Na+-Ca2+ exchanger in calcium homeostasis.
- To assess the contribution of intracellular calcium stores to calcium regulation.
Main Methods:
- Measurement of intracellular Ca2+ and Na+ concentrations using fluorescent dyes fura-2 and SBFI in situ.
- Voltage clamping of leech (Hirudo medicinalis) giant glial cells.
- Inhibition of ion transport mechanisms using ouabain, cyclopiazonic acid, and orthovanadate.
- Manipulation of extracellular ionic composition (Na+-free saline).
Main Results:
- Basal intracellular Ca2+ concentration was maintained at low levels (approx. 75-80 nM).
- Removal of external Na+ caused a small, reversible increase in [Ca2+]i.
- Inhibition of the plasma membrane Ca2+-ATPase (using vanadate) led to a significant increase in basal [Ca2+]i and slowed Ca2+ extrusion.
- Inhibition of endoplasmic reticulum Ca2+-ATPase (using cyclopiazonic acid) transiently increased [Ca2+]i and slowed recovery from Ca2+ loads.
- Na+-Ca2+ exchanger activity appeared minor under basal conditions but became significant when the plasma membrane Ca2+-ATPase was inhibited.
Conclusions:
- The plasma membrane Ca2+-ATPase is the primary mechanism for extruding Ca2+ and maintaining low basal [Ca2+]i in leech glial cells.
- Intracellular calcium stores contribute minimally to the recovery of basal [Ca2+]i after a load.
- The Na+-Ca2+ exchanger plays a secondary role in basal [Ca2+]i maintenance but is important for Ca2+ extrusion when the plasma membrane Ca2+-ATPase is compromised.