Adenylyl cyclase activity and its modulation in the gills of Mytilus galloprovincialis exposed to Cr6+ and Cu2+.
The adenylyl cyclase (AC)/cAMP system regulates a large number of physiological functions in bivalve mussels, although its basal properties and the potential effects of environmental pollutants are scarcely studied. We characterized some properties of AC and measured both the enzyme activity and the cAMP levels in the gills of the filter-feeding sea mussel Mytilus galloprovincialis. Basal AC activity was 5.6+/-0.8 pmol cAMP 10 min(-1) mg protein(-1) and showed a Km value of 0.82+/-0.06 mM for ATP in the presence of 5mM Mg2+. It was stimulated up to 2.5- and 3.5-fold by 5-HT and GTPgammaS, respectively. Similarly to what was found in other bivalves, forskolin is a poor activator that reached significant stimulation only at 100 microM. Both basal and 5-HT-stimulated AC activity were significantly increased in the gills of mussels exposed for 7 days in aquaria to Cr6+ (10 ng/l) and Cu2+ (5 microg/l). The cAMP content of the gill under these conditions was also significantly higher than in control animals. In vitro exposure of gill membrane preparations to Cr6+ and Cu2+ induced a bimodal effect. Cu2+ significantly stimulated AC activity at nanomolar concentrations, but a strong inhibition was displayed in the micromolar range. A similar bell-shaped curve was obtained in the presence of Cr6+, with maximal AC stimulation at 10(-8)M and inhibition at 10(-5)M. Overall, these data suggest that the mussel AC/cAMP system can be affected with different patterns by heavy metals. AC activity is strongly affected by acute exposure to heavy metals in vitro, probably through a direct interaction of the pollutants with the enzyme molecule, while AC activity and cAMP content increase in organisms exposed for 7 days in vivo, probably as a defense response to acclimate the physiological functions to the environmental challenge.
Fabbri
Elena
E
University of Bologna, Interdepartment Centre for Research in Environmental Sciences (CIRSA), Via S. Alberto 163, 48100 Ravenna, Italy.
Capuzzo
Antonio
A
D000262:Adenylyl Cyclases / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002857:Chromium / Q000633:toxicity*; D003300:Copper / Q000633:toxicity*; D000242:Cyclic AMP / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004781:Environmental Exposure; D005880:Gills / Q000187:drug effects / Q000201:enzymology; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D049878:Mytilus / Q000187:drug effects* / Q000201:enzymology; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D014874:Water Pollutants, Chemical; D002857:Chromium; D003300:Copper; D000242:Cyclic AMP; D000262:Adenylyl Cyclases