Calmodulin and Cell Function

Introduction: The importance of calcium in the regulation of cell function has become increasingly recognized in the past 20 years. It is now known that changes in intracellular calcium concentration, like changes in adenosine 3′:5′-monophosphate (cyclic AMP), are of crucial importance in stimulus-response coupling. Thus, the second messenger theory originally proposed by Sutherland et al. [1], in which a hormone or nerve impulse is first messenger and cyclic AMP the second intracellular messenger, has been expanded to include calcium ions as well as cyclic nucleotides. Moreover, there is now evidence in many cellular systems that calcium ions and cyclic nucleotides act as dual interrelated messengers [2], and, therefore, some cellular processes are regulated by calcium as well as by cyclic nucleotides, as shown in Table 1. Evidence has accumulated that it is changes in free intracellular calcium concentration that are, in some way, responsible for activation of the enzymes involved in the processes shown in this Table.