Introduction

Abstract

When you hold this book in your hands, the activated muscles of your arms and hands receive contraction signals from motoneurons that release acetylcholine, a neurotransmitter, at the nerve-muscle junction. The message conveyed to the muscle is then relayed through a series of ion channels in the cell membrane which ultimately lead to the release of calcium ions from intracellular calcium stores which then activate the contractile proteins. Whereas the events at the nerve-muscle junction are now well understood, much less is known about the mechanism of calcium release and calcium activation of the contractile machinery. Here, we shall consider these problems and how they can be solved by interdisciplinary approaches involving physiology, biophysics and molecular biology. In addition, the strength of the comparative approach will also become apparent, in view of the diversity of the different kinds of striated and smooth muscles. Yet there is unity in this diversity. In all muscle studied so far, contraction appears to be basically an interaction of two proteins, actin and myosin, which is more or less precisely controlled by the intracellular calcium ion concentration. This principle of calcium control is so essential for muscle contraction and cell motility that it has been conserved during evolution for more than a billion years. How diverse, on the other hand, are the mechanisms controlling the intracellular calcium ion concentration, the intracellular calcium target proteins and the way in which calcium ions activate the contractile system! For instance, in fast skeletal muscle calcium is handled entirely within the cell by the sarcoplasmic reticulum, whereas in smooth and cardiac muscle the extracellular calcium supply seems to be quite important.