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G Proteins Immunodetection and Adrenergic Transduction Pathways in the Liver of Anguilla anguilla
Federico Caselli, Antonio Capuzzo, Annamaria Piano, Paola Valbonesi and Elena Fabbri
Physiological and Biochemical Zoology: Ecological and Evolutionary Approaches
Vol. 75, No. 6 (November/December 2002), pp. 609-616
Published by: The University of Chicago Press. Sponsored by the Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology
Stable URL: http://www.jstor.org/stable/10.1086/345483
Page Count: 8
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Abstract G proteins are members of a highly conserved superfamily of GTPases, which includes heterotrimeric (α, β, γ) proteins acting as critical control points for transmembrane signaling. In ectothermal vertebrates, knowledge about these proteins is scarce, and our work provides the first demonstration that Gs, Gq, and Gi proteins are all present in the liver of a fish. Gqα subunits of about 42 kDa have been identified in European eel (Anguilla anguilla) liver membranes, supporting previous reports about the existence of hormone transduction pathways coupled to inositol 1,4,5‐trisphosphate/Ca2+ enhancement in fish hepatocytes. Although two Gsα proteins of about 45 and 52 kDa have been reported in mammals, a single isoform of approximately 45 kDa has been recognized in eel liver. Gsα and Gqα proteins are involved in the epinephrine transduction pathway, leading to cAMP and Ca2+ intracellular increments, respectively. Interestingly, both messengers significantly stimulated glucose release from eel hepatocytes but with a different time course. In fact, the Ca2+‐dependent glucose output preceded the cAMP‐mediated release by about 7 min. Giα subunits of about 40 kDa were also immunodetected, suggesting the presence of hormone receptors leading to adenylyl cyclase inhibition in eel liver; however, α2‐ adrenoreceptor ligands were ineffective on both enzyme activity and glucose release.
© 2002 by The University of Chicago. All rights reserved.