ABSTRACT
Specific cell membrane receptor proteins interact with primary messengers (hormones, growth factors, external physical and chemical stumili) to trigger a sequence of biochemical events which work as a channel of information transfer. Following the interaction of primary messengers with their receptors, systems of ‘second messengers’ transduce extracellular signals into a biochemical and biophysical language understood by the cell machinery and transfer the signal from the membrane to target signalling proteins. This results in the cells performing the biological effect triggered by the signal (for example: DNA synthesis and cell division by growth factors) or, if the signal is aggressive, in inducing them to reply appropriately by a defence and adaptive mechanism. It is fascinating to consider that the cell contains thousands of signalling proteins and only about ten second messengers. The calcium ion (Ca2+) is a second messenger playing a key role in responses of the cell to environmental and hormonal signals as well as in some intrinsic developmental processes. Additional information may be present in transient calcium signals as a result of single channel opening (termed ‘blips’) or the opening of synchronized clusters of channels (termed ‘puffs’) spatially restricted within the cell. Oscillation frequency, amplitude, duration and number can also be involved in the regulation of given cellular responses (Adler, 2002).
