Dual control of cytosolic metals by lysosomal transporters in lobster hepatopancreas

Abstract

SUMMARY This study describes the membrane transport mechanisms used by lobster (Homarus americanus) hepatopancreatic epithelial lysosomes to accumulate and sequester heavy metals from the cytosol, and thereby aid in the regulation of these ions entering the animal from dietary constituents. The present investigation extends previous work describing lysosomal metal uptake by cation exchange with protons and suggests that a second, parallel, lysosomal transport process involving metal—thiol conjugates may work in conjunction with the cation antiporter to control cytoplasmic metal concentrations. Transport of 65Zn2+ by lysosomal membrane vesicles (LMV) incubated in 1 mmol l−1 glutathione (GSH) was not significantly different from metal transport in the absence of the tripeptide. However, preloading LMV with 1 mmol l−1 α-ketoglutarate (AKG), and then incubating in a medium containing 1 mmol l−1 GSH, more than doubled metal uptake, compared with vesicles equilibrated with chloride or possessing an outwardly directed chloride gradient. Kinetic analysis of lysosomal 65Zn2+ influx as a function of zinc concentration, in vesicles containing 1 mmol l−1 AKG and incubated in 1 mmol l−1 GSH, revealed the presence of a sigmoidal, low affinity, high capacity carrier process transporting the metal into the organelle. These data indicated the possible presence of an organic anion exchanger in lobster lysosomal membranes. Western blot analysis of LMV with a rabbit anti-rat OAT1 antibody showed the presence of an orthologous OAT1-like protein (approximate molecular mass of 80 kDa) signal from these membranes. These results, and those published previously, suggest the occurrence of two metal transporters on hepatopancreatic membranes, a high affinity, low capacity cation antiporter and a low affinity, high capacity organic anion exchanger. Together these two systems have the potential to regulate cytoplasmic metals over a wide concentration range.

Cytochemical characterization of gill and hepatopancreatic cells of the crab Ucides cordatus (Crustacea, Brachyura) validated by cell metal transport

“…The hepatopancreas of crustaceans, on the other hand, play a role in absorption and nutrient storage, digestive enzyme synthesis, detoxification of xenobiotics and calcium balance (Lyon & simkiss, 1984;Chavez-Crooker et al, 2001;ziLLi et al, 2003;PaGanini & BianChini, 2009;sterLinG et al, 2010). There are four cell types responsible for these functions: 1.…”

Análises Geoquímicas e respostas Ecotoxicológicas na Avaliação da Qualidade Ambiental de uma Área Estuarina Protegida

“…Hypoxic environment tend to diminish GSH levels, indicating that LPO in this case was not caused by low oxygen levels (Hauser-Davis et al, 2014). Although, this enzyme has also the capacity to chelate metals (Sterling et al, 2010;Wang et al, 2008), inhibiting the detoxification activation system. Togni (2007) reinforce the anti-xenobiotic function of GST, since only abiotic factors variation, without the presence of contaminants, tend to not affect the activity of GST.…”