Factors Affecting the Distribution of Acetylcholine Receptors in Innervated and Denervated Skeletal Muscle Fibres

Abstract

Publisher Summary This chapter discusses the factors affecting the distribution of acetylcholine (ACh) receptors in innervated and denervated skeletal muscle fibres. At birth, the fibres of mammalian muscles are sensitive to ACh over their entire surface membrane. As the muscles mature ACh receptors become confined to the end-plate region. The motor nerve plays an essential role in the establishment and maintenance of the normal distribution of ACh receptors. Following section of the motor nerve adult muscle fibres again become sensitive to ACh over their entire membrane and desensitization of the extra-junctional muscle membrane fails to take place in denervated young muscles. It has been suggested that the nerve governs the distribution of ACh receptors by suppressing receptor manufacture. It was proposed that following denervation release of this suppression leads to the appearance of extra-junctional ACh receptors. However, there is constant turnover of ACh receptors at the neuromuscular junction and the normal muscle must manufacture receptors to incorporate them at the neuromuscular junction. In the presence of degenerating nerve, or following denervation or muscle injury an inflammatory reaction occurs and extra-junctional ACh receptors appear. It was proposed that the appearance of extra-junctional ACh receptors following denervation or muscle injury was due to the exposure or activation of ACh receptors present at extra-junctional membrane by enzymes released by inflammatory cells.