Calcium: outside/inside homeostasis and signalling

More and more data accumulate concerning calcium dependent effects in all compartments of cells. The higher the organism in evolution the more calcium becomes involved. Inspection of the data while looking for an explanation of the involvement of calcium in metabolism, nuclear functions, control over pumps, external activities, mineralisation and so on leads one to suppose that calcium has an integrating function. The implication is that calcium flow is a large network connecting the environment, the cytoplasm, vesicles, organelles, the nucleus and in higher species, organs. There is the possibility then that calcium ion functions are being analysed, often in vitro, in a bit by bit reductionist manner while in vivo calcium is the equivalent of an electron in complicated electrical circuits. We then should look for its connections to energy, to effects where conformational switching by calcium pulses is equivalent to magnetic triggering by electron flow and where storage in vesicles is equivalent to condenser-like devices and so on. The appearance of pulsing, of time delays in parts of circuits, and other properties of electronic circuits seen in calcium triggering are then explicable as part of calcium circuit design. No other ion can operate in the same way due to the peculiarities of the calcium ion, its size, charge, ionisation potential and its availability which allow it both to flow rapidly yet to bind considerably. (C) 1998 Elsevier Science B.V. All rights reserved.