Physiological implications of the interaction between the plasma membrane calcium pump and nNOS.

The tight regulation of intracellular calcium levels is essential for the normal function of a great many cellular processes, and disruption of this regulation, resulting in sustained increases in intracellular-free calcium, has been associated with numerous diseases. One of the several transporters involved in calcium homeostasis is a P-type ATPase known as the plasma membrane calcium/calmodulin-dependent ATPase (PMCA) which is involved in calcium extrusion from the cytosol to the extracellular compartment. It has long been established that in many cell types, in particular non-excitable cells, the primary role of PMCA is in the bulk transport of intracellular calcium; however, its role in excitable cells is less clear. In the heart, for example, calcium is essential for contractile function as well as being a key messenger in signal transduction pathways; however, the mechanisms by which the cardiomyocyte distinguishes between these roles of calcium remain unclear. It is perhaps the transporters not involved in the contractile cycle (such as PMCA) that are able to carry non-contractile signals. This review will highlight the role of PMCA as a modulator of signal transduction pathways and in particular the role of isoform 4 in the regulation of the nitric oxide signalling pathway.