Aquaporin 1 Is Involved in Acid Secretion by Ionocytes of Zebrafish Embryos through Facilitating CO2 Transport.
Mammalian aquaporin 1 (AQP1) is well known to function as a membrane channel for H2O and CO2 transport. Zebrafish AQP1a.1 (the homologue of mammalian AQP1) was recently identified in ionocytes of embryos; however its role in ionocytes is still unclear. In this study, we hypothesized that zebrafish AQP1a.1 is involved in the acid secretion by ionocytes through facilitating H2O and CO2 diffusion. A real-time PCR showed that mRNA levels of AQP1a.1 in embryos were induced by exposure to 1% CO2 hypercapnia for 3 days. In situ hybridization and immunohistochemistry showed that the AQP1a.1 transcript was highly expressed by acid-secreting ionocytes, i.e., H+-ATPase-rich (HR) cells. A scanning ion-selective electrode technique (SIET) was applied to analyze CO2-induced H+ secretion by individual ionocytes in embryos. H+ secretion by HR cells remarkably increased after a transient loading of CO2 (1% for 10 min). AQP1a.1 knockdown with morpholino oligonucleotides decreased the H+ secretion of HR cells by about half and limited the CO2 stimulated increase. In addition, exposure to an AQP inhibitor (PCMB) for 10 min also suppressed CO2-induced H+ secretion. Results from this study support our hypothesis and provide in vivo evidence of the physiological role of AQP1 in CO2 transport.
Department of Anatomy and Cell Biology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
Jiun-Lin
JL
Horng
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Pei-Lin
PL
Chao
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Po-Yen
PY
Chen
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Tin-Han
TH
Shih
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
Li-Yih
LY
Lin
D000143:Acids / Q000378:metabolism; D000818:Animals; D051398:Aquaporin 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D006180:Proton-Translocating ATPases / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D012867:Skin / Q000166:cytology / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D000143:Acids; D012333:RNA, Messenger; D029961:Zebrafish Proteins; D002245:Carbon Dioxide; D051398:Aquaporin 1; D006180:Proton-Translocating ATPases