Copper transport by lobster (Homarus americanus) hepatopancreatic mitochondria

Mechanisms of copper transport into purified mitochondrial suspensions prepared from the hepatopancreas of the Atlantic lobster Homarus americanus were investigated. Mitochondria were purified by combining methods of differential and Percoll-gradient centrifugation, and copper transport was studied using the copper-sensitive fluorescent dye Phen Green. Copper transport by this mitochondrial preparation was kinetically the sum of saturable and non-saturable transfer components. Addition of 500 μmol l^–1 Ca²⁺ or 500 nmol l^–1 Ruthenium Red abolished the non-saturable copper transport component, significantly (P<0.01) reduced the apparent binding affinity of the saturable transport component, but was without effect (P>0.05) on the apparent maximal transport velocity of the saturable transfer process. The antiport inhibitor diltiazem (500 μmol l^–1) acted as a mixed inhibitor of the saturable transport mechanism, but had no effect on the non-saturable component of transfer. These results suggest that the non-saturable copper influx process was probably by way of the well-known Ruthenium-Red-sensitive Ca²⁺ uniporter and that the saturable transport component was probably due to a combination of both the Na⁺-dependent, diltiazem-sensitive 1Ca²⁺/2Na⁺ antiporter and the Na⁺-independent, diltiazem-insensitive 1Ca²⁺/2H⁺ antiporter. A model is discussed relating these mitochondrial copper uptake processes to the transfer of metal ions across the epithelial brush-border membrane.