| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2004: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2003: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
Patients with diabetes mellitus who do not take xerogenic drugs often complain of dry-mouth symptoms, xerostomia. It remains unknown, however, whether aquaporin-5 (AQP5) is subjected to regulated trafficking in salivary gland cells of diabetic rats. In this study, we investigated the difference of subcellular localization of AQP5 in parotid glands of control and streptozocin-induced diabetic (diabetic) rats stimulated by the muscarinic agonist, cevimeline. Cevimeline induced an increase in the amount of AQP5 in the apical plasma membrane (APM) in parotid cells of control rats, but not diabetic rats. Immunohistochemical study indicated that AQP5 fluorescence, under unstimulated conditions, was colocalized with flotillin-2 and GM1 fluorescence in a diffuse pattern in the parotid cytoplasm of both control and diabetic rats. Ten minutes after intravenous injection of cevimeline, AQP5 fluorescence was dramatically increased together with flotillin-2 and GM1 fluorescence in the APM of the pa
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rotid cells of control rats, but not diabetic rats. Sixty minutes after the injection, there was diffuse pattern of fluorescence in the cytoplasm of control rats. The total amount of AQP5 did not decrease significantly in parotid cells of diabetic rats, but there was a significant increase in the amount of AQP5 mRNA in these cells. Administration of insulin to diabetic rats produced the cevimeline-induced trafficking of AQP5 with lipid rafts to the APM in parotid cells and the recovery of the amount of AQP5 mRNA in the cells, as observed in control rats. These findings indicate that AQP5 synthesis in rat parotid cells is not affected by diabetes mellitus at the translation step, but rather at the transcription step. Treatment of the parotid tissues with cevimeline for 10 min induced a decrease in the solubility of AQP5 by 1 % Triton X-100 in control rats, but not in diabetic rats, indicating that after trafficking with lipid rafts to the APM, AQP5 dissociates from lipid rafts to non-rafts in the APM in parotid cells. The results suggest that the impaired AQP5 translocation with lipid rafts to the APM in salivary gland cells in response to muscarinic agonists results in diabetic xerostomia. Less
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