Cell signaling, beyond cytosolic calcium in eukaryotes

Calcium functions as a secondary messenger within the cytosols of eukaryotes. This serves as a reference point to evaluate three related questions:1.Calcium, as well as cyclic AMP, also functions as a paracrine messenger; how specific and extensive is this use?2.Calcium binding proteins and calcium extrusion mechanisms have been identified in prokaryotes; does it function as a messenger?3.The concentrations of other divalent cations, especially zinc and magnesium, are well regulated and perturbations have specific physiological impacts; are these divalents involved in information transfer?Exploration of these three interrelated questions indicates the importance of more sensitive techniques and of a refined concept of information transfer and transduction.