Cadmium is acutely toxic for murine hepatocytes: effects on intracellular free Ca2+ homeostasis

Abstract

We studied cadmium toxicity in murine hepatocytes in vitro. Cadmium effects on intracellular free Ca(2+) concentration ([Ca(2+)](i)) were assayed, using a laser scanning confocal microscope with a fluorescent probe, Fluo-3/AM. The results showed that administration of cadmium chloride (CdCl(2), 5, 10, 25 microM) resulted in a dose-dependent decrease of hepatocyte viability and an elevated aspartate aminotransferase (AST) activity in the culture medium (p<0.05 for 25 microM CdCl(2) vs. control). Significant increases of lactate dehydrogenase (LDH) activities in 10 and 25 microM CdC1(2)-exposed groups were observed (p<0.05 and p<0.01, respectively). A greatly decreased albumin content and a more malondialdehyde (MDA) formation also occurred after CdC1(2) treatment. The Ca(2+) concentrations in the culture medium of CdCl(2)-exposed hepatocytes were significantly decreased, while [Ca(2+)](i) appeared to be significantly elevated (p<0.05 or p<0.01 vs. control). We found that in Ca(2+)-containing hydroxyethyl piperazine ethanesulfonic acid-buffered salt solution (HBSS) only, CdCl(2) elicited [Ca(2+)](i) increases, which comprised an initially slow ascent and a strong elevated phase. However, in Ca(2+)-containing HBSS with addition of 2-aminoethoxydiphenyl borane (2-APB), CdCl(2) caused a mild [Ca(2+)](i) elevation in the absence of an initial rise phase. Removal of extracellular Ca(2+) showed that CdCl(2) induced an initially slow [Ca(2+)](i) rise alone without being followed by a markedly elevated phase, but in a Ca(2+)-free HBSS with addition of 2-APB, CdCl(2) failed to elicit the [Ca(2+)](i) elevation. These results suggest that abnormal Ca(2+) homeostasis due to cadmium may be an important mechanism of the development of the toxic effect in murine hepatocytes. [Ca(2+)](i) elevation in acutely cadmium-exposed hepatocytes is closely related to the extracellular Ca(2+) entry and an excessive release of Ca(2+) from intracellular stores.