Regulation of Water Channel Activity of Aquaporin 1 by Arginine Vasopressin and Atrial Natriuretic Peptide

Aquaporin 1 (AQP1), a six-transmembrane domain protein that functions as a water channel, is present in many fluid secreting and absorbing tissues such as kidney, brain, heart, and eye. It is believed that among the five known mammalian aquaporins, kidney aquaporin (AQP2) is the only water channel that is regulated by arginine vasopressin (AVP). The present data suggest that AQP1 may also be regulated by AVP. The application of AVP to Xenopus oocytes injected with AQP1 cRNA increased the membrane permeability to water. In addition, our data reveal that atrial natriuretic peptide (ANP), a peptide hormone that plays an important role in the regulation of body fluid homeostasis, blocks the AQP1-mediated increase in water permeability. Incubation with 8-bromo-cAMP or direct 8-bromo-cAMP injection into oocytes expressing AQP1 cRNA significantly increased membrane permeability to water, suggesting that stimulation of AQP1 activity by AVP may involve a cAMP-dependent mechanism. Regulation of water permeability by AVP and ANP has potential relevance to active water transport in a variety of tissues that express AQP1 including kidney, brain, and eye.