Cd2+ and Hg2+ affect glucose release and cAMP-dependent transduction pathway in isolated eel hepatocytes.
Isolated hepatocytes of the European eel (Anguilla anguilla) have been used as experimental model to characterize the effects of Cd(2+) and Hg(2+) on either basal or epinephrine-stimulated glucose release. Cd(2+) strongly reduced glucose output from cells perifused in BioGel P4 columns and challenged with epinephrine, with a maximum inhibition of 95% reached at 10 microM (IC(50) 0.04 microM). The epinephrine-stimulated glucose output was also reduced by Hg(2+), although a significant inhibition of about 60% was achieved only at 10 microM (IC(50) 5 microM). The possible influence of Cd(2+) and Hg(2+) on adenylyl cyclase/cAMP transduction pathway has been investigated, since this system is known to play a pivotal role in the regulation of fish liver glycogen breakdown and consequent glucose release. Micromolar concentrations of both heavy metals significantly reduced the epinephrine-modulated cAMP levels in isolated eel hepatocytes, in good agreement with the reduction of glucose output. Cd(2+) and Hg(2+) also significantly reduced basal and epinephrine-stimulated adenylyl cyclase activity in liver membrane preparations. A competitive inhibition with respect to Mg(2+) was shown by Cd(2+) and Hg(2+), which significantly reduced the affinity of the allosteric activator for the adenylyl cyclase system. Apparent Km for Mg(2+) was 4.35 mM in basal conditions, and increased to 9.1 and 7.1 mM in the presence of 10 microM Cd(2+) and Hg(2+), respectively. These results indicate that Cd(2+) and Hg(2+) may impair a crucial intracellular transduction pathway involved in the adrenergic control of glucose metabolism, but also in several other routes of hormonal regulation of liver functions.
Fabbri
Elena
E
Interdepartment Centre for Research in Environmental Science, University of Bologna, via Tombesi dall'Ova 55, 48 100, Ravenna, Italy. e.fabbri@ambra.unibo.it
Caselli
Federico
F
Piano
Annamaria
A
Sartor
Giorgio
G
Capuzzo
Antonio
A
D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism; D000811:Anguilla; D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008628:Mercury / Q000633:toxicity*; D015398:Signal Transduction / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D014874:Water Pollutants, Chemical; D002104:Cadmium; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D008628:Mercury; D008274:Magnesium; D005947:Glucose; D004837:Epinephrine