Abstract
[Purpose] Aquaporin5 (AQP5) is a water-selective channel protein and located at apical membranes of the acinar cells of the lacrimal glands. The tear secretion is regulated exactly by on/off mechanism, suggesting that AQP5 is regulated by gating. However, the gating mechanisms are still unknown. Our purpose is to clarify the gating mechanisms of AQP5 in the lacrimal gland acinar cells. [Methods] Poly(A) RNAs from the lacrimal glands were prepared from 5-6 week-old BALB/c mouse. The poly(A) RNAs and AQP5 cRNA were microinjected into Xenopus laevis oocytes to examine if AQP5 inhibitory factor exists in the lacrimal glands. The inhibitory factors were purified from the mouse lacrimal glands by affinity chromatography. [Results] The osmotic water permeability of AQP5 was inhibited by the co-injection of poly(A)RNAs from the lacrimal glands into oocytes. In addition, dibutyryl-cAMP and C-terminal peptide of AQP5 restored the suppressed water permeability of AQP5 oocytes. Using affinity chromatography, odorant-binding protein-1a (OBP-1a) is isolated from mouse lacrimal glands as one of the inhibitory factors for AQP5. OBP-Ia is abundantly expressed in lacrimal glands. Antisense DNA to OBP-1a also restored the suppressed water permeability of AQP5 oocytes. [Conclusion] AQP5 is gated by binding of OBP-1a to the C-terminus of the molecule, which may be regulated by phosphorylation. Tear secretion might be regulated by the gating of AQP5. [Jpn J Physiol 55 Suppl:S35 (2005)]
