Effects of natural point mutation of rat aquaporin 5 expressed in vitro on its capacity of water permeability and membrane trafficking.

In the colony of Sprague-Dawley (SD) strain, we found that there were rats expressing a mutant AQP5, which has a point mutation at nt 308 (G308A), leading to a replacement of (103)Gly with (103)Asp in the 3rd transmembrane domain. The mutant molecule scarcely expressed in the acinar cells, probably because of ineffective trafficking. The mutant molecule, however, showed normal water permeability when assessed by the oocyte system.

A naturally occurring point mutation in the rat aquaporin 5 gene, influencing its protein production by and secretion of water from salivary glands.

A greater than twofold diversity in the expression level of aquaporin 5 (AQP5) has been observed in the membrane fraction of the submandibular gland (SMG) in Sprague-Dawley rats (Murdiastuti K, Miki O, Yao C, Parvin MN, Kosugi-Tanaka C, Akamatsu T, Kanamori N, and Hosoi K. Pflügers Arch 445: 405-412, 2002). In the present study, breeding between brother and sister rats was repeated within high AQP5 producers and low ones to obtain inbred offspring.

AQP and the control of fluid transport in a salivary gland.

Experiments were performed with the perfused rat submandibular gland in vitro to investigate the nature of the coupling between transported salt and water by varying the osmolarity of the source bath and observing the changes in secretory volume flow. Glands were submitted to hypertonic step changes by changing the saline perfusate to one containing different levels of sucrose. The flow rate responded by falling to a lower value, establishing a new steady-state flow.

Lipopolysaccharide-induced elevation and secretion of interleukin-1beta in the submandibular gland of male mice.

The intraperitoneal injection of lipopolysaccharide (LPS) (400 microg/kg body weight) induced the expression of mRNAs of inflammatory cytokines such as interleukin (IL)-1beta, IL-6 and tumour necrosis factor (TNF)-alpha in the submandibular gland (SMG) of C3H/HeN mice but not that of C3H/HeJ mice, a mutant strain for Toll-like receptor-4 (TLR-4(-) mutant). The mRNA levels of these cytokines in the SMG of the wild-type mice increased as early as 3 hr after injection, peaked at 3-6 hr, and had decreased again by 24 hr. In this study, we particularly focused on IL-1beta, and induction by this endotoxin was investigated in detail.

Downregulation of AQP2 expression in the kidney of polydipsic STR/N mice.

Aquaporin-2 (AQP2) is responsible for the concentration of urine in the kidney collecting tubule under the regulation of vasopressin. The mRNA level of this water channel in polydipsic STR/N mice was extremely reduced compared with that in normal ICR mice. In male mice, reduction of the AQP2 mRNA level was not evident at 3 wk of age, at which time water intake was not increased.