Enhancement of Metallothionein Gene Expression in Male Wistar (WF/NCR) Rats by Treatment with Calmodulin Inhibitors: Potential Role of Calcium Regulatory Pathways in Metallothionein Induction

Abstract

Recent reports indicate that calmodulin inhibitors (CIs) can modify cadmium toxicity in rodents. For instance, pretreatment with CIs prevents cadmium-induced testicular damage in mice and substantially reduces such damage in rats, the latter effect coinciding with significant alterations in cadmium distribution. Although the basis of these effects is unclear, it is frequently observed that metal-binding proteins such as metallothionein (MT) are involved in acquired tolerance to cadmium and this could be true of tolerance induced by CIs. Thus, we examined the effects of various CIs on MT gene expression. Treatment of WF/NCr rats with known CIs, including trifluoperazine (TPZ), N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W7), calmidazolium (CMZ), chlorpromazine (CPZ), and the calcium ionophore, A23187, increased hepatic MT gene expression, as assessed by mRNA levels, in all cases. Furthermore, hepatic MT protein levels were 40 to 180 μg MT/g wet wt (g ww) in rats treated with CIs or A23187 compared to control levels of 10 μg MT/g ww. Treatment with CPZ and CMZ did not increase renal MT protein after exposure, although increases in renal MT mRNA were observed. However, the CIs TPZ and W7 and the calcium ionophore increased both renal MT protein and MT mRNA levels. In contrast, no increases in testicular MT mRNA or the testicular cadmium binding protein (TCBP) levels were seen with any of the treatments. Treatment with CIs or A23187 produced increases in zinc levels in the liver, but not in the kidneys or testes. These results indicate that CIs, such as TPZ, W7, CMZ, and CPZ, as well as the calcium ionophore A23187, have a marked stimulatory effect on hepatic and renal MT gene expression and that calcium regulatory pathways may play an important role in this induction of MT.