The AQP-3 water channel is a pivotal modulator of glycerol-induced chloride channel activation in nasopharyngeal carcinoma cells

Abstract

Aquaporin (AQP) and chloride channels are ubiquitous in virtually all living cells, playing pivotal roles in cell proliferation, migration and apoptosis. We previously reported that AQP-3 aquaglyceroporin and ClC-3 chloride channels could form complexes to regulate cell volume in nasopharyngeal carcinoma cells. In this study, the roles of AQP-3 in their hetero-complexes were further investigated. Glycerol entered the cells via AQP-3 and induced two different Cl− currents through cell swelling-dependent or -independent pathways. The swelling-dependent Cl− current was significantly inhibited by pretreatment with CuCl2 and AQP-3-siRNA. After siRNA-induced AQP-3 knock-down, the 140mM glycerol isoosmotic solution swelled cells by 22% (45% in AQP-3-intact cells) and induced a smaller Cl− current; this current was smaller than that activated by 8% cell volume swelling, which induced by the 140mM glycerol hyperosmotic solution in AQP-3-intact cells. This suggests that the interaction between AQP-3 and ClC-3 plays an important role in cell volume regulation and that AQP-3 may be a modulator that opens volume-regulated chloride channels. The swelling-independent Cl− current, which was activated by extracellular glycerol, was reduced by CuCl2 and AQP-3-siRNA pretreatment. Dialyzing glycerol into cells via the pipette directly induced the swelling-independent Cl− current; however this current was blocked by AQP-3 down-regulation, suggesting AQP-3 is essential for the opening of chloride channels. In conclusion, AQP-3 is the pathway for water, glycerol and other small solutes to enter cells, and it may be an essential modulator for the gating of chloride channels.