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Protective effects of Ca2+ channel blockers against methyl mercury toxicity
M Sakamoto1, N Ikegami, A Nakano
1Department of Epidemiology, National Institute for Minamata Disease, Minamata City, Japan.
Abstract:
The protective effects of Ca2+ channel blockers against the toxicity of methyl mercury were examined by both in vivo and in vitro experiments. In the in vivo study we first examined the effects of the Ca2+ channel blockers (20 mg/kg/day), flunarizine, nifedipine, nicardipine, and verapamil against the toxic level of methyl mercury treatment (5 mg/kg/day of methyl mercuric chloride for 12 consecutive days). However, there was a difference in potency of the effects among the reagents. All the Ca2+ channel blockers prevented a decrease in body weight and/or the appearance of the symptoms of neurological disorders in the rats treated with methyl mercury. In the next experiment, we examined flunarizine at different levels of supplementation (1, 25 and 50 mg/kg/day). Flunarizine in a dose-dependent manner prevented a decrease in body weight, appearance of the symptoms of neurological disorder and mortality in the rats treated with methyl mercury. Flunarizine treatment (25 mg/kg/day) for the first 5 days did not affect mercury distribution among the tissues, suggesting that the mechanism of protection against methyl mercury-induced toxicity may be attributed to its own pharmacological effect. In the in vitro study we examined the effect of flunarizine (0, 0.5, 5 and 50 microM) using primary cultures of cerebellar granular cells in 96-well culture plates. Viable cell numbers were estimated 1 and 3 days after treatment with methyl mercury. The estimated 50% lethal concentration (LC50) of methyl mercury was higher in plates treated with 5 and 50 microM of flunarizine both on days 1 and 3, indicating that flunarizine protected the primary cultured cerebellar granular cells against the toxicity of methyl mercury. As such, Ca2+ channel blockers protected against the toxicity of methyl mercury both in vivo and in vitro, suggesting that Ca2+ plays an important role in the mechanisms of methyl mercury toxicity.
Insights
Calcium (Ca2+) channel blockers protect against methyl mercury toxicity. Studies showed these blockers, including flunarizine, prevented neurological symptoms and mortality in rats and protected cells in vitro, highlighting calcium's role in mercury toxicity.
Area of Science:
- Neuroscience
- Toxicology
- Pharmacology
Background:
- Methyl mercury is a potent neurotoxin.
- Calcium ions (Ca2+) are implicated in cellular toxicity mechanisms.
- Ca2+ channel blockers are used to manage various cardiovascular and neurological conditions.
Purpose of the Study:
- To investigate the protective effects of Ca2+ channel blockers against methyl mercury toxicity.
- To evaluate the efficacy of different Ca2+ channel blockers in vivo and in vitro.
- To explore the role of Ca2+ in the mechanism of methyl mercury toxicity.
Main Methods:
- In vivo studies using rats treated with methyl mercury and Ca2+ channel blockers (flunarizine, nifedipine, nicardipine, verapamil).
- Dose-response evaluation of flunarizine in vivo.
- In vitro studies using primary cerebellar granular cells exposed to methyl mercury and flunarizine.
- Assessment of body weight, neurological symptoms, mortality, and cell viability.
Main Results:
- All tested Ca2+ channel blockers demonstrated protective effects against methyl mercury toxicity in vivo.
- Flunarizine showed a dose-dependent protective effect, reducing neurological symptoms and mortality.
- In vitro, flunarizine increased the 50% lethal concentration of methyl mercury, protecting cerebellar cells.
Conclusions:
- Ca2+ channel blockers effectively protect against methyl mercury toxicity both in vivo and in vitro.
- Flunarizine exhibits significant protective properties against methyl mercury-induced neurotoxicity.
- These findings suggest a critical role for Ca2+ in the pathogenesis of methyl mercury toxicity.