NEUROTOXIC EFFECTS OF CYANIDE AND THE ROLE OF CALCIUM (DILTIAZEM, TREMORS)
Abstract
The effect of cyanide on neuronal calcium regulation was investigated in mice to determine the role of calcium in mediating neurotoxic events commonly observed following cyanide poisoning. KCN, 10 mg/kg, sc, significantly increased whole brain total calcium (WBTC) levels from 48.1 (+OR-) 1.8 to 66.5 (+OR-) 3.9 (mu)g/g dry weight after 15 min. The levels remained elevated for 3 hours and returned to control readings after 12 hours. KCN, 10 to 15 mg/kg, significantly elevated the WBTC after 30 min. Pretreatment with the calcium channel blocker diltiazem, 600 (mu)g/kg, iv, 15 min before KCN blocked the cyanide-induced rise in WBTC. Cyanide-induced tremors, which are a centrally mediated sign of intoxication, were quantified and correlated with the observed changes in WBTC. The severity, time profile and dose-response relationship of cyanide-induced tremors paralleled the results obtained from the same parameters in the WBTC studies. Also, pretreatment with diltiazem prevented the cyanide-induced tremors. The effect of cyanide on cytosolic calcium levels was measured fluorometrically with quin II in PC12 cells. Resting cytosolic calcium levels, 115.0 (+OR-) 4.9 nM, gradually and steadily increased following addition of KCN in concentrations of 10('-4), 10('-3) and 10('-2) M. The cytosolic calcium levels increased to 156.0 (+OR-) 16.9 and 253.3 (+OR-) 45.5 nM at 10('-4) KCN; 368.0 (+OR-) 70.1 and 711.3 (+OR-) 51.4 nM at 10('-3) M KCN; and 629.0 (+OR-) 26.2 and 821.0 (+OR-) 103.0 nM at 10('-2) M KCN after 15 and 30 min, respectively. Cells depolarized with K('+), 50 mM, produced a rapid and immediate increase in cytosolic calcium levels of 202.3 (+OR-) 16.2, 296.8 (+OR-) 14.7 and 371.3 (+OR-) 26.6 nM after 5, 15 and 30 min, respectively. KCN, 10('-3) M, produced a statistically significant increase in cytosolic calcium after 5 min in depolarized cells relative to cells treated with KCN alone but not K('+) alone. Pretreatment of the cells with diltiazem, 10('-5) M, or pentobarbital, 10('-6) M, agents with calcium channel blocking properties, blocked the cyanide and/or K('+)-induced cytosolic calcium rise. KCN and/or A23187, a calcium ionophore, produced small transient increases in cytosolic calcium when cells were bathed in calcium free media suggesting intracellular mobilization plays a minor role in supplying calcium during the cyanide-induced calcium accumulation. These studies suggest that intraneuronal calcium may play an important role in mediating cyanide neurotoxicity and calcium channel blocking agents may be useful in limiting the severity of the centrally mediated symptoms of acute cyanide intoxication.
Degree
Ph.D.
Subject Area
Pharmacology
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