The purpose of the present volume is to give a comprehensive and up-to-date 2 survey of the nature and role of calcium ions (Ca +) in the regulation of cel­ 2 lular function. Since Ca + has gained in interest over the past years as a cel­ lular messenger in signal transduction, and since the discovery of its cellular receptor protein, calmodulin, has helped in understanding its mode of action in molecular terms, we felt that an interdisciplinary selection of topics from the calcium field could provide a good source of information for all those in­ terested in calcium-mediated physiology. The volume begins with an overview on the synarchic nature of the two 2 cellular messengers, cyclic AMP and Ca +. The next three chapters deal with 2 the various transport mechanisms for Ca +. The biochemistry and molecular biology of calmodulin, as well as the cellular localization of calmodulin and calmodulin-binding proteins, are reviewed. Calcium regulation of smooth muscle contraction introduces the pharmacology of calcium antagonists.