Dual functional characteristic of human aquaporin 10 for solute transport.

BACKGROUND/AIMS: Although aquaglyceroporins have been generally believed to operate in a channel mode, which is of nonsaturable nature, for glycerol as well as for water, we recently found that human aquaporin 9 (hAQP9) operates in a carrier-mediated mode, which is of saturable nature, for glycerol. Based on the finding, we assumed that such a characteristic might be shared by the other aquaglyceroporins and examined the functional characteristics of hAQP10, which is an intestine-specific aquaglyceroporin.

METHODS

Transport assays were conducted using Xenopus laevis oocytes expressing hAQP10 derived from the microinjected cRNA.

RESULTS

The transport of glycerol by hAQP10 was found to be highly saturable with a Michaelis constant of 10.4 μM and specifically inhibited by several glycerol analogs such as monoacetin. Furthermore, when glycerol was preloaded in hAQP10-expressing oocytes, its efflux was trans-stimulated by extracellular glycerol. These results indicate the involvement of a carrier-mediated mechanism in glycerol transport by hAQP10. Interestingly, a channel mechanism was also found to be involved in part in hAQP10-mediated glycerol transport.

CONCLUSION

The present study unveiled the uniquely dual functional characteristic of hAQP10 as a carrier/channel for solute transport, providing a novel insight into its operation mechanism, which would help further elucidate its physiological role.