Important insights in to the function of members of the TRP (transient receptor potential) channel superfamily have been gained from the identification of disease-related mutations. In particular the identification of mutations in the PKD2 gene in autosomal dominant polycystic kidney disease has revealed a link between TRP channel function, mechanosensation and the role of the primary cilium in renal cyst formation. The PKD2 gene encodes TRPP2 (transient receptor potential polycystin 2) that has significant homology to voltage-activated calcium and sodium TRP channels. It interacts with polycystin-1 to form a large membrane-associated complex that is localized to the renal primary cilium. Functional characterization of this polycystin complex reveals that it can respond to mechanical stimuli such as flow, resulting in influx of extracellular calcium and release of calcium from intracellular stores. TRPP2 is expressed in the endoplasmic reticulum/sarcoplasmic reticulum where it also regulates intracellular calcium signalling. Therefore TRPP2 modulates many cellular processes via intracellular calcium-dependent signalling pathways.