TRPC1, CALCIUM, AND SALIVA SECRETION

Saliva performs a number of extremely important biological functions that are instrumental in maintaining oral health. It has been estimated that more than 5 million people in the US suffers from salivary gland dysfunction. Secretion of saliva is driven by concerted activities of a number of ion channels and transporters. Although, it is believed that calcium is the primary intracellular factor that regulates fluid secretion, the molecular mechanism involved in the regulation of cytosolic calcium is not clearly understood. This is primarily due to the lack of information regarding the mechanism of regulation of calcium channels present in salivary glands. Furthermore, no information is available as how increase in cytosolic calcium modulates saliva secretion. Moreover, in Sjgren's syndrome patients, although the acinar tissues appear to be normal, they do not function properly and have a decreased calcium response to agonist-stimulation. This observation raises the possibility that calcium channels might be altered in this pathological condition. Results obtained from our awarded grant indicate that TRPC1 is the primary calcium channel in salivary glands and is intimately involved saliva secretion. To understand the regulation of TRPC1 channel we have shown that in human submandibular gland cells, TRPC1 interaction with STIM1, Cav1, and Orai1 dictates TRPC1 mediated calcium entry. Furthermore, these protein-protein interactions were confined to specific domains in the plasma membrane, however nothing is known if similar mechanisms are also present in vivo in salivary gland tissues. Therefore, in this renewal we intend to thoroughly characterize the role of cytosolic calcium in salivary gland function and to determine the relationship between transient receptor potential canonical (TRPC1) -1 and saliva secretion. The hypothesis of this study is that because calcium influx via TRPC1 plays a pivotal role in the physiological function of salivary glands, characterization of calcium channels in salivary glands will be important to understand the mechanism of saliva secretion, which could represent as drug targets in salivary gland dysfunction. We will coordinate our efforts in order todetermine the functional significance of TRPC1 channel in regulating saliva secretion and how it leads to salivary gland destruction. We will also investigate the role of lipid rafts in the assembly/activation of the TRPC1 channel in mouse submandibular gland cells and will identify the mechanism involved in the regulation of TRPC1 via STIM1 and Orai1. The results of our studies are expected to provide new insights into the role of calcium channels and the molecular mechanism involved in saliva secretion. Greater understanding of these events responsible for saliva secretion will be important in elucidating new therapy for salivary gland dysfunctions.