SARCOPLASMIC RETICULUM AND OTHER MEMBRANES IN THE REGULATION OF SKELETAL MUSCLE CONTRACTION AND RELAXATION, A MULTILEVEL APPROACH

Abstract

The skeletal muscle fiber is a giant multinucleate cell, extending centimeters in length, and up to 100μ in diameter. The bulk of the mass of the fast twitch skeletal muscle fiber is occupied by myofibrils that run the length of fiber. There can be hundreds of myofibrils in a single muscle fiber. The myofibril consists of a linear array of sarcomeres (approximately 2.5 μ long and 1 μ in diameter), the structural units that carry out muscle contraction and relaxation. The number of sarcomeres in a fibril depends on the length of the fiber. Muscle contraction and relaxation are controlled by the intra-fiber free Ca ++ concentration, [Ca ++ ] i , in the myoplasm that bathes the muscle filaments of the sarcomeres. In turn, the [Ca ++ ] i is controlled by a network of membranes that regulate and coordinate the process in time and space. This chapter illustrates the structure of a mammalian striated-muscle fiber. It also illustrates a longitudinal section of a rabbit's skeletal muscle fiber. The chapter presents molecular biology approach for the study of sarcoplasmic reticulum (SR). It discusses the reconstitution approach to correlate membrane composition with structure and function and to characterize the nature of lipid–protein interactions in the SR membrane.