Acetylcholine receptors are decreased in:September 2009

Ans. D: Myasthenia gravisMyasthenia gravis is a serious and sometimes fatal disease in which skeletal muscles are weak and tire easily. It is caused by the formation of circulating antibodies to the muscle type of nicotinic acetylcholine receptors. These antibodies destroy some of the receptors and bind others to neighboring receptors, triggering their removal by endocytosis. The reason for the development of autoimmunity to acetylcholine receptors in this disease is still unknown. Another condition that resembles myasthenia gravis is Lambe-Eaton syndrome. In this condition, muscle weakness is caused by antibodies against one of the Ca2+ channels in the nerve endings at the neuromuscular junction. This decreases the normal Ca2+ influx that causes acetylcholine release. However, muscle strength increases with prolonged contractions as more Ca2+ is released.