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First published online October 19, 2007
Journal of Experimental Biology 210, 3771-3779 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.008037

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G protein activation by uncaging of GTP--S in the leech giant glial cell

Ingo C. Hirth, Frank C. Britz and Joachim W. Deitmer^*

Abteilung für Allgemeine Zoologie, FB Biologie, TU Kaiserslautern, PO Box 3049, D-67653 Kaiserslautern, Germany

^* Author for correspondence (e-mail: deitmer{at}biologie.uni-kl.de)

Accepted 13 August 2007

Glial cells can be activated by neurotransmitters via metabotropic, G protein-coupled receptors. We have studied the effects of `global' G protein activation by GTP--S on the membrane potential, membrane conductance, intracellular Ca²⁺ and Na⁺ of the giant glial cell in isolated ganglia of the leech Hirudo medicinalis. Uncaging GTP--S (injected into a giant glial cell as caged compound) by moderate UV illumination hyperpolarized the membrane due to an increase in K⁺ conductance. Uncaging GTP--S also evoked rises in cytosolic Ca²⁺ and Na⁺, both of which were suppressed after depleting the intracellular Ca²⁺ stores with cyclopiazonic acid (20 µmol l^–1). Uncaging inositol-trisphosphate evoked a transient rise in cytosolic Ca²⁺ and Na⁺ but no change in membrane potential. Injection of the fast Ca²⁺ chelator BAPTA or depletion of intracellular Ca²⁺ stores did not suppress the membrane hyperpolarization induced by uncaging GTP--S. Our results suggest that global activation of G proteins in the leech giant glial cell results in a rise of Ca²⁺-independent membrane K⁺ conductance, a rise of cytosolic Ca²⁺, due to release from intracellular stores, and a rise of cytosolic Na⁺, presumably due to increased Na⁺/Ca²⁺ exchange.

Key words: K⁺ conductance, cytosolic Ca²⁺, cytosolic Na⁺, Na⁺/Ca²⁺ exchange, BAPTA