EFFECTS OF HG2-RETICULUM (PECTEN JACOBAEUS) - PROTECTIVE ROLE OF GLUTATHIONE( ON CA2+ DYNAMICS IN THE SCALLOP SARCOPLASMIC)

Scallop (Pecten jacobaeus) sarcoplasmic reticulum (SR) vesicles were f unctionally characterized and tested for Hg2+ effects. An SR-containin g 20,000 g supernatant from adductor muscle homogenate was incubated w ith fluo-3, allowing free Ca2+ variations to be spectrofluorimetricall y followed. Data showed an ATP-dependent thapsigargin-sensitive Ca2+ u ptake, revealing the activity of the SR Ca2+ ATPase. Treatment with ry anodine elicited Ca2+ release, showing the presence of ryanodine sensi tive Ca2+ channels, whereas InsP(3) caused negligible effects. Exposur e to different concentrations of Hg2+ (1-50 mu M) produced a dose depe ndent Ca2+ release from SR vesicles, which was shown to depend on both Ca2+ ATPase inhibition and Ca2+ channel opening. Hg2+ binding to sulf hydryls was pointed out by incubation with Thiolyte, whereas an involv ement of sulfhydryls in Ca2+ release was assessed by treatment with th e sulfhydryl reagent N-ethylmaleimide (NEM). Yet, conversely to Hg2+, NEM seemed unable to open Ca2+ channels, suggesting that the latter ef fect occurs via some specific heavy metal interaction, possibly involv ing sulfhydryls not available to larger molecules or even components o ther than sulfhydryls. Pre incubation of SR with reduced glutathione ( GSH) largely prevented Hg2+ effects, whereas a certain reduction of me tal injury also occurred by adding GSH after Hg2+ exposure, thus confi rming the role of GSH as a first line of defense against heavy metals. Copyright (C) 1997 Elsevier Science Inc.