SCIENCE BASED RESEARCH

Science Based Research

ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

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Science Based Research

Abstract

In the past five years, skeletal muscle has emerged as a paradigm of “nitric oxide” (NO) function and redox-related signaling in biology. All major nitric oxide synthase (NOS) isoforms, including a muscle-specific splice variant of neuronal-type (n) NOS, are expressed in skeletal muscles of all mammals. Expression and localization of NOS isoforms are dependent on age and developmental stage, innervation and activity, history of exposure to cytokines and growth factors, and muscle fiber type and species. nNOS in particular may show a fast-twitch muscle predominance. Muscle NOS localization and activity are regulated by a number of protein-protein interactions and co- and/or posttranslational modifications. Subcellular compartmentalization of the NOSs enables distinct functions that are mediated by increases in cGMP and byS-nitrosylation of proteins such as the ryanodine receptor-calcium release channel. Skeletal muscle functions regulated by NO or related molecules include force production (excitation-contraction coupling), autoregulation of blood flow, myocyte differentiation, respiration, and glucose homeostasis. These studies provide new insights into fundamental aspects of muscle physiology, cell biology, ion channel physiology, calcium homeostasis, signal transduction, and the biochemistry of redox-related systems.

Introduction

Nitric oxide synthases (NOSs) are the products of three genes. They are named after the cells or systems from which they were originally purified in order of their discovery and are thus designated neuronal (n) NOS (NOS1), macrophage (immune)/calcium calmodulin-independent or “inducible” (i) NOS (NOS2), and endothelial (e) NOS (NOS3). The numerical designation has come into vogue with the more recent appreciation that each of the NOSs in fact has a wide tissue distribution. In contrast, the classification of NOSs as “constitutive” or inducible has turned out to be unreliable because each of the isoforms may be regulated dynamically; inducibility is a function of the stimulus rather than the gene product. Alternative splicing factors are important in the pattern of NOS expression. In particular, nNOS in mature skeletal muscle and heart contains a 34-amino acid insert that arises from alternative splicing of nNOS pre-RNA between exons 16 and 17. The muscle isoform is called nNOSµ. Three distinct cDNAs, exon 1 variants arising from alternative promoters of a single nNOS gene, are robustly expressed in skeletal muscle

Rationale of the Research

Skeletal muscle mass declines with age and this appear to be primarily a consequence of type II fiber atrophy and fiber loss. Force production of single muscle fibers is reduced with age. Excess free radical and reactive oxygen species production is postulated to contribute to age-related changes of muscle, contraction-induced damage, and as a factor in the pathogenesis of neuromuscular ...