Molecular Basis of K+ Current During Secretion

点击翻译按钮获取中文摘要

Salivary gland hypofunction enhances the risk of oral and systemic disease, and results in a deterioration in the ability to chew, swallow, and speak. The secretion of saliva helps to maintain oral health by lubricating and hydrating mucosal surfaces, as well as protecting the oral cavity from mechanical and chemical stresses and microbial invasion. The process of secretion couples the action of multiple ion channels, co-transporters, and exchangers to drive the transepithelial movement of water. In particular, a calcium-activated potassium channel located on the basolateral membrane of acinar cells is coupled to a calcium-activated chloride channel on the apical membrane, and these channels work together to allow stimulated secretion by muscarinic agonists. The molecular identity of each of these channels remains unknown. Until recently, the large-conductance BK (slo) channel was thought to carry the majority of the calcium-activated potassium current during stimulated secretion. However, pharmacological evidence exists that secretion in the submandibular gland occurs primarily through the action of an intermediate-conductance calcium-activated potassium channel. A candidate cDNA, termed SK4/IK1, was recently cloned based upon homology with the SK family of small-conductance calcium-activated potassium channels. Over the range of tissues examined, the highest level of expression of the human IK isoform, hIK1, occurs in salivary glands. To better define the involvement of IK1 in stimulated secretion, we propose to use molecular and immunological tools to localize the IK1 transcript and protein in the parotid gland of a mouse model system. We will further exploit the utility of this system by studying the physiological consequences of the loss of mIK1 activity. Using a transgenic strain containing a targeted gene disruption of mIK1 which we are generating presently, we will examine mIK1-mediated changes in saliva flow rate and ion composition. Because recombinant mIK1 has been suggested to convey a novel ability to undergo regulatory volume decrease (RVD) in Xenopus oocytes, we will further assay whether mIK1 is involved in RVD in a mammalian expression system and in the parotid gland. Finally, we will look at compensatory changes that occur in the expression of functionally-related ion transport proteins in the transgenic strain.