Different effects of Hg2+ and Cu2+ on mussel (Mytilus galloprovincialis) plasma membrane Ca2+-ATPase: Hg2+ induction of protein expression.
Deregulation of Ca2+ homeostasis can produce serious effects on cell functioning due to an alteration of Ca2+ signaling. The aim of this study was to evaluate variations in plasma membrane Ca2+-ATPase (PMCA) induced in mussels by in vivo exposure to Cu2+ or Hg2+. PMCA activity was assayed using a cytochemical method allowing localization and in situ quantification of Ca2+-ATPase on cryostat tissue sections. The effects of fixed concentrations of Cu2+ (0.6 microM) or Hg2+ (1.3 microM) were evaluated after different times of exposure (1, 4, 6 days), while those of increasing amounts of Cu2+ (0.3, 0.6, 1.3 microM) or of Hg2+ (0.6, 1.3, 2.4 microM) were evaluated after 4 days. Cu2+ produces dose-dependent inhibition of PMCA in the digestive gland, with a minimum at the fourth day of treatment and a recovery at the sixth day. Conversely, Hg2+ induces a significant rise of PMCA activity, with a maximum at the fourth day. Similar results have been found after biochemical assay of PMCA, using plasma membranes obtained from density-gradient separation of gill homogenates. PMCA expression has been assessed by immunoprecipitation and Western immunoblotting on digestive gland homogenates, showing an induction after exposure to Hg2+ but not to Cu2+. In conclusion, Cu2+ does not vary PMCA expression but reduces PMCA activity, indicating PMCA inhibition; conversely, Hg2+ increases PMCA expression more than PMCA activity, suggesting that it also produces PMCA inhibition, but the induction of PMCA expression leads to a net increase in enzyme activity.
Burlando
B
B
Dipartimento di Scienze dell'Ambiente e della Vita, Università del Piemonte Orientale "A. Avogadro", Via Bellini 25 G, 15100 Alessandria, Italy. burlando@unipmn.it
Bonomo
M
M
Caprì
F
F
Mancinelli
G
G
Pons
G
G
Viarengo
A
A
D000818:Animals; D049872:Bivalvia / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D003300:Copper / Q000633:toxicity*; D004064:Digestive System / Q000187:drug effects / Q000201:enzymology; D005880:Gills / Q000187:drug effects / Q000201:enzymology; D008628:Mercury / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D014874:Water Pollutants, Chemical; D003300:Copper; D000252:Calcium-Transporting ATPases; D008628:Mercury; D002118:Calcium