The quality of life for millions of Americans is adversely affected by salivary gland hypofunction caused by a variety of etiologies including systemic diseases, radiation therapy, xerogenic medications, and Sj6gren's syndrome. The development of interventions to restore function for these individuals requires a thorough understanding of the molecular physiology of salivary glands. Salivary secretion involves a two-step process: acinar cells initially secrete an isotonic, plasma-like fluid; duct cells subsequently modify this primary secretion to conserve NaC1. Both the fluid secretion and NaC1 reabsorption processes are dependent upon the coordinated action of multiple Na+ transport mechanisms including Na+/H+ exchangers, Na+ channels, and Na+/K+/2C1- co-transporters. Genetically modified mice have proven to be valuable models of human salivary gland dysfunction, and are useful for confirming the molecular identities and the functional properties of important Na+ transporters. Nevertheless, significant gaps remain in our understanding of the function of the major Na+ transporting proteins. To address remaining questions, we propose a molecular and functional comparison of Na+ transporter physiology in human and mouse salivary glands. We will test the overall hypothesis that Na+ transport proteins are critical to saliva formation. Specifically:
Aim 1) will take advantage of genetically modified mice generated by targeted disruption of the Na+ channel ENaC (Scrmla) and the Na+/H+ exchanger Nhe4 [Slc9a4) genes to directly test whether these Na+ transport proteins are essential for salivary gland secretion;
Aim 2) will assess whether agonists that mobilize intracellular Ca 2+, or increase the intracellular cAMP content, acutely regulate the activity of the different Na+ transport mechanisms in human and mouse salivary cells;
and Aim 8) will determine whether gene disruption affects saliva production through systemic or gland-specific mechanisms. Ultimately, the information gained from these Aims will aid in the development of therapies to remedy various forms of salivary gland dysfunction.
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