Role of extracellular zinc and copper on metallothionein regulation in cultured rat hepatocytes.

Cellular and extracellular metallothionein contents of rat hepatocytes cultured in the presence of albumin (30 mumol/L) with zinc (1, 10, 50 and 100 mumol/L), copper (1, 10 and 50 mumol/L), zinc and copper (1, 10 and 50 mumol/L of each metal) or no metals in the culture medium have been measured by radioimmunoassay. Cellular metallothionein levels increased steadily with culture time regardless of the metal treatment and showed little dependence (only a twofold increase) on extracellular zinc or copper at all metal concentrations and times (up to 3 days) studied. In contrast, the presence of both metals simultaneously in the culture medium strongly increased cellular metallothionein contents, acting synergistically in some cases. Significant extracellular metallothionein was observed when copper or zinc and copper were present in the culture medium, most of which is likely a consequence of cell leakage because no evidence of physiological secretion was observed. Total metallothionein production (cellular and extracellular metallothionein levels) indicated that copper was a better metallothionein inducer than zinc in these experimental conditions. These results indicate that metallothionein regulation in the hepatocyte is different depending on the extracellular metal levels and composition and that attention must be given to metallothionein release from the hepatocyte.