G protein activation by uncaging of GTP-gamma-S in the leech giant glial cell.
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-gamma-S on the membrane potential, membrane conductance, intracellular Ca(2+) and Na(+) of the giant glial cell in isolated ganglia of the leech Hirudo medicinalis. Uncaging GTP-gamma-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-gamma-S also evoked rises in cytosolic Ca(2+) and Na+, both of which were suppressed after depleting the intracellular Ca(2+) stores with cyclopiazonic acid (20 micromol l(-1)). Uncaging inositol-trisphosphate evoked a transient rise in cytosolic Ca(2+) and Na+ but no change in membrane potential. Injection of the fast Ca(2+) chelator BAPTA or depletion of intracellular Ca(2+) stores did not suppress the membrane hyperpolarization induced by uncaging GTP-gamma-S. Our results suggest that global activation of G proteins in the leech giant glial cell results in a rise of Ca(2+)-independent membrane K+ conductance, a rise of cytosolic Ca(2+), due to release from intracellular stores, and a rise of cytosolic Na+, presumably due to increased Na+/Ca(2+) exchange.
Hirth
Ingo C
IC
Abteilung für Allgemeine Zoologie, FB Biologie, TU Kaiserslautern, Kaiserslautern, Germany.
Britz
Frank C
FC
Deitmer
Joachim W
JW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology / Q000528:radiation effects; D047709:Hirudo medicinalis / Q000166:cytology / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009457:Neuroglia / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism; D014466:Ultraviolet Rays
C057003:1-(2-nitro)phenylethyl-P(3)-guanosine 5'-O-(3-thio)triphosphate; D007295:Inositol Phosphates; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D012964:Sodium; D019204:GTP-Binding Proteins; D011188:Potassium; D002118:Calcium