Calcium signalling and secretory epithelia

Ca2+ is now firmly established as the most important intracellular regulator of physiological and pathological events in a vast number of different cell types, including secretory epithelia. In these tissues, Ca2+ signalling is crucially important for the control of both fluid secretion and electrolyte secretion as well as the regulation of macromolecule secretion. In this overview article, I shall attempt to give some general background to the concepts underlying our current thinking about Ca2+ signalling in epithelia and its roles in regulating secretion. It is outside the scope of this review to provide a comprehensive account of Ca2+ signalling and the many different processes in the many different secretory epithelia that are controlled by Ca2+ signals. It is my aim to draw attention to some general features of Ca2+ signalling processes in secretory epithelia, which are rather different from those in, for example, endocrine glands. The principal examples will be taken from studies of exocrine cells and, in particular, pancreatic acinar cells, as they are the pioneer cells with regard to investigations of Ca2+ signalling due to primary intracellular Ca2+ release. They also represent the cell type which has been characterized in most detail with regard to Ca2+ transport events and mechanisms