Calcium signalling in smooth muscle is complex, intimately involved in the regulation of a diverse range of cellular processes including cell differentiation, proliferation, gene expression, contraction and apoptosis. Intracellular calcium signals are initiated via calcium entry from the extracellular space and calcium mobilisation from intracellular sarcoplasmic reticulum calcium stores by inositol 1,4,5-trisphosphate and opening of ryanodine receptors (RYRs). The spatio-temporal pattern of these signals is thought to facilitate the diversity of cellular responses to calcium. Heterogeneity amongst ion channels, calcium pump distribution and the spatial organisation of other elements such as contractile filaments, mitochondria and sarcoplasmic reticulum are thought to play an important part in determining local and global transmission of the calcium signal, as well as the frequency of the signals, within the cell (Pabelick et al. 2001). It is important therefore to understand the expression patterns/profiles of calcium regulatory proteins and relate them to cell function.
