Methylmercury induced neuromuscular dysfunction in the rat

Rats were exposed to 20 mg/kg methylmercury for 10-18 days. The isolated phrenic nerve-hemidiaphragms from these animals demonstrated a reduced capability to maintain contraction amplitude when stimulated at a frequency of 10/sec. The addition of neostigmine directly to the organ bath produced a contraction enhancement significantly lower than normal. In a different series of isolated preparations, it was demonstrated that methylmercury at a final bath concentration of 2 x 10(-5) M could inhibit contractions completely with only a small degree of recovery. The muscles still responded to direct stimulation and nerve action potentials appeared unchanged. These observations may account for the muscular weakness in methylmercury intoxicated rats.