抄録
The diffusive water permeability of mouse parotid acinar cells was measured by 1H nuclear magnetic resonance relaxation method using an extracellular relaxation reagent, gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA). The rate constant for water efflux from the acinar cell suspension was estimated to be ca. 5 s−1 at 28oC which would be consistent with diffusive water permeability (Pd) of ca. 1.4 x 10−3 cm/s. This value is the same range of those obtained in perfused rat submandibular gland, Necturus gallbladder and human red blood cells (1.6 to 4.7 x 10−3 cm/s). Activation energy of water transport through the cell membrane (Ea) was estimated from temperature dependence (5-30oC) of the rate constant for water efflux. From the slope of Arrenius plot, Ea value is estimated to be 4.6 ± 0.6 kcal/mol. This activation energy is much smaller than that obtained in the lipid bilayer vesicles (12- 14 kcal/mol), and is the same range of red blood cells with AQP1 (Ea = 5 kcal/mol). Thus, this indicates that water transport of acinar cells should be done by a channel-mediated pathway, and suggests contribution of AQP5. A potential inhibitor of AQP5 water channel, 50 uM HgCl2, was applied to the acinar cells. The rate constant for water efflux from the cells did not change significantly, but only a tendency to decrease. Since 50 uM of HgCl2 is a half of 100 uM used for perfused rat submandibular gland, it is possible that Hg2+ did not reach the effective concentration to inhibit AQP5. [J Physiol Sci. 2007;57 Suppl:S87]
