Abstract
[Objective] The glycolipid- and cholesterol-rich membrane microdomains are lateral components of the plasma membranes and considered to function as platforms for both signal transduction and membrane trafficking. However, role of membrane microdomains in salivary glands has not been elucidated. In this study, we isolated membrane microdomains of rat parotid secretory granules using sucrose density ultracentrifugation, and compared the components of membrane microdomains in the process of the granule maturation. [Methods] Secretory granules in the rat parotid gland were purified using percoll. The components of membrane microdomains are biochemically separated as detergent-resistant membranes (DRMs) based on their insolubility in the detergent. [Results] When DRMs separated using detergent 1% Triton X-100, Syntaxin 6, VAMP-2 and munc-18 were recovered in GM1a-rich DRMs fraction. On the other hand, when DRMs separated using detergent 1% Brij-58, Syntaxin 6 detected in the different fraction from GM1a-rich one. In the parotid gland of rat treated with isoproterenol for 8 hours, formation of new secretory granules was observed with electron microscopy. In the granule Brij-58 insoluble DRMs, Syntaxin 6 was distributed in GM1a-rich fraction. [Conclusion] These results suggest that Syntaxin 6 exists on GM1a-rich microdomains in immature granule. For the granule maturation, exclusion of Syntaxin 6 from GM1a-rich microdomain appears to be important. [Jpn J Physiol 55 Suppl:S71 (2005)]
