Neuroendocrine signalling: natural variations on a Ca2+ theme.

This special issue on Ca(2+) signalling in neuroendocrine cells is an opportunity to assess, through a range of first-class review articles, the complex world of endocrine signalling, a complexity that is probably best captured by calling it "diversity in unity". The unity comes from the fact that all the endocrine cells are excitable cells, able to generate action potentials and are using Ca(2+) as an essential informational molecule, coupling cell stimulation with the activation of secretion, through the exocytotic process. The 'diversity' element, illustrated by almost all the reviews, stems from the modalities employed to achieve the increase in cytosolic Ca(2+) signal, the balance between the participation of Ca(2+) entry through the plasma membrane voltage-operated Ca(2+) channels and the release of Ca(2+) from intracellular Ca(2+) stores, and the cross-talk between the Ca(2+) and cyclic AMP signalling pathways.