Fluoride-induced hyperkalemia: the role of Ca2+-dependent K+ channels.
Acute fluoride poisoning is associated with sudden cardiac death by an unknown mechanism. Because F- binds to Ca2+ to cause marked hypocalcemia, lowered serum Ca2+ concentrations have been thought to be a major underlying factor in the ventricular irritability of F(-)-toxic patients. However, correction of the hypocalcemia does not prevent sudden death. Paradoxically, while decreasing extracellular Ca2+ levels, in vitro studies have shown F- increases intracellular Ca2+, which is thought to trigger Ca2+-dependent K+ channels and produce a K+ efflux. The K+ efflux may be important clinically, as patients with F- overdose can exhibit hyperkalemia shortly before cardiovascular collapse. In erythrocyte suspensions, we found that propranolol, which increases the sensitivity of the Ca2+-dependent K+ channels, exacerbates the efflux, and quinidine, which blocks the channel, prevents the efflux. In six dogs, 35 mg/kg of sodium fluoride given intravenously produced intractable ventricular fibrillation within 140 minutes. Four dogs given 200 mg of quinidine sulfate with the sodium fluoride developed no ventricular arrhythmias. The data indicate that F--induced hyperkalemia is important in sudden cardiac death following acute fluoride toxicity and that this hyperkalemia is mediated by Ca2+-dependent K+ channels.