The broad long-range goal of this research is to understand on a molecular level the mechanisms by which neurotransmitters promote receptor-mediated increases in saliva formation (fluid and electrolyte secretion) in parotid acinar cells. Salivary dysfunction and salivary diseases (including Sjogren's Syndrome) present significant oral health concerns as well as quality of life issues. Clinically, individuals experiencing salivary gland hypofunction (reduced salivary flow rates) have difficulty in swallowing, increased risks of dental caries and oral fungal infections, and alterations in taste. Thoughtful consideration of these problems and how to treat them necessitates a full understanding of fluid and protein secretion by salivary glands. Parotid cells and salivary glands have served as model systems to explore the coupling between signaling events and the initiation of secretion. The overall sequence of events of receptor binding, phospholipase C activation, [Ca2+]i elevation, and the opening of Ca2+-sensitive ion channels has been well characterized. Although this sequence serves as a template for the initiation of secretion in salivary and other exocrine cells, recent research has provided a much more detailed scheme of the events involved in secretion at multiple levels within this overall scheme. This proposal originates from several of our observation relating to cell metabolism, ion transport, and the activation of cell signaling proteins. Several experimental results indicate that AMP-dependent protein kinase (AMPK) activation affects multiple parotid signaling and functional processes, and that ERK1/2 and the Na,K-ATPase exhibit a bi-directional communication. To gain a more complete understanding of parotid acinar cell function, we propose the following interrelated Specific Aims:
Aim 1 is to determine the molecular details of the bi-directional signaling between the Na,K-ATPase and ERK1/2.
Aim 2 is to determine if the alpha-1 subunit of the Na,K-ATPase is phosphorylated by kinases in carbachol-treated parotid acinar cells.
Aim 3 is to examine the contribution of ERK1/2 and changes in intracellular Na to the Na,K-ATPase activity in CIO cells, an immortalized parotid acinar cell line. We will use electrophysiological techniques to resolve questions that we are unable to address using native parotid cells.
Aim 4 is to examine regulatory changes in parotid acinar cell signaling and function when intracellular ATP is reduced.
Aim 5 is to determine the involvement of AMPK in parotid cell signaling and function. AMPK is activated in an ouabain-dependent manner by receptor ligands that increase the Na,K-ATPase activity. We suggest that these areas of investigation will provide a more complete understanding of parotid cell function, and thereby contribute to future therapies to aid salivary dysfunction. ? ? ?
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