Calcium signalling in non-excitable cells: notes on oscillations and store refilling

Technical advances in studying cellular calcium concentrations, and discoveries about many aspects of signal transduction have transformed this field of biology since this Journal was launched a decade ago. At that time monitoring of the key variable, cytoplasmic free Ca2+ concentration [Ca2+]i, was possible with aequorin or arsenazo ill mainly in large invertebrate cells, though pioneering work with aequorin micro-injection into cardiac and smooth muscle had just started. At that time there was also intense activity by a few groups aiming to make Ca-selective micro-electrodes selective and sharp enough to measure [Ca2+]i in small cells. Also the use of electropermeabilized cells had begun to allow the defining of the concentrations of Ca2+ required to activate secretion in mammalian cells. Nearly all this work and all the relevant electrophysiology relating to calcium signalling had been done in excitable cells, basically muscle and nerve, and was aimed at understanding contraction, transmitter release and neurosecretion, and the control of membrane permeability. Recent advances have now allowed [Ca2+]i to be measured in non-excitable cells.