G Proteins Immunodetection and Adrenergic Transduction Pathways in the Liver ofAnguilla anguilla

Abstract

G proteins are members of a highly conserved superfamily of GTPases, which includes heterotrimeric (alpha, beta, gamma) 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 G(s), G(q), and G(i) proteins are all present in the liver of a fish. G(q)alpha 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/Ca(2+) enhancement in fish hepatocytes. Although two G(s)alpha 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. G(s)alpha and G(q)alpha proteins are involved in the epinephrine transduction pathway, leading to cAMP and Ca(2+) intracellular increments, respectively. Interestingly, both messengers significantly stimulated glucose release from eel hepatocytes but with a different time course. In fact, the Ca(2+)-dependent glucose output preceded the cAMP-mediated release by about 7 min. G(i)alpha subunits of about 40 kDa were also immunodetected, suggesting the presence of hormone receptors leading to adenylyl cyclase inhibition in eel liver; however, alpha(2)- adrenoreceptor ligands were ineffective on both enzyme activity and glucose release.

Selection of best-performing reference gene products for investigating transcriptional regulation across silvering in the European eel (Anguilla anguilla)

“…In this study, isolated hepatocytes were used to set up a methodological approach for our ongoing investigations on transcriptional changes underlying metabolic adaptations of European eels during silvering and the possible influence of environmental stressors on such processes. This is in line with our previous studies addressing the physiological regulation of liver metabolism 31 , and the effects of environmental pollutants on such processes 32 33 . Besides our specific research interests, the qPCR normalization strategy proposed here may have a widespread application in the numerous experimental approaches employing transcriptional assays in fish hepatocytes (reviewed by Moon 34 ).…”

Binding kinetics and sequencing of hepatic α1‐adrenergic receptors in two marine teleosts, Mackerel (Scomber scombrus) and Anchovy (Engraulis encrasicolus)

“…Eventually, evidence was obtained for an alternative Ca 21 -mediated mechanism in fish (Zhang et al,'92;Moon et al,'93), followed by confirmation of the presence of a 1 -ARs physiologically coupled to phospholipase C/IP 3 -Ca 21 signaling in isolated hepatocytes (Fabbri et al,'95b,'99b;'95). It is now accepted that a-and b-ARs are simultaneously present and operative in the liver of fish (Caselli et al, 2002) as in mammals (Sulakhe et al,'88).…”