ENaC- and CFTR-dependent ion and fluid transport in human middle ear epithelial cells.
Ion channels, such as the epithelial sodium channel (ENaC), are essential for maintaining a fluid-free middle ear cavity by controlling periciliary fluid. Deviations from the normal volume or compositions of periciliary fluid are probably responsible for otitis media with effusion. To elucidate the physiologic roles of the ENaC and cystic fibrosis transmembrane conductance regulator (CFTR) in the middle ear mucosa, we compared the electrophysiological activity and protein expressions of ENaC and CFTR in normal human middle ear epithelial (NHMEE) cells with those in normal human nasal epithelial (NHNE) cells. We also evaluated the role of ENaC and CFTR in fluid transport by NHMEE cells. Short-circuit current (Isc) was measured in cell monolayers by modified Ussing chambers. Immunoblotting was performed for ENaC and CFTR. In addition, transepithelial fluid transport was measured after loading 100 microl of fluid onto the luminal cell surface. The amiloride-sensitive Isc in NHMEE cells was much larger than in NHNE cells, whereas the forskolin-induced Isc, presumably mediated by CFTR, was significantly smaller in NHMEE cells. ENaC subunits alpha, beta, and gamma were all detected in NHMEE cells, and their expressions were stronger than those in NHNE cells. In comparison, CFTR was also detected in the middle ear mucosa, but at a lower expression level than in NHNE cells. NHMEE cells showed more amiloride-sensitive fluid absorption than NHNE cells. In contrast, fluid absorption was less sensitive to forskolin/IBMX in NHMEE cells than in NHNE cells. The ATP induced Cl- efflux and the amplitude of ATP-induced current in NHMEE cells was much larger than in NHNE cells. In the present study, we have demonstrated an enhanced amiloride-sensitive Isc and fluid absorption in NHMEE cells, where the role of CFTR is limited. Our data also suggest that the ATP-induced Cl- channel could be an alternative Cl- channel to CFTR in NHMEE cells.
Choi
Jae Young
JY
Department of Otorhinolaryngology, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-gu Seoul, 120-752, Republic of Korea.
Son
Eun Jin
EJ
Kim
Jung Lim
JL
Lee
Joo-Hyeung
JH
Park
Hun Yi
HY
Kim
Sung Huhn
SH
Song
Mee Hyun
MH
Yoon
Joo-Heon
JH
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004432:Ear, Middle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D053503:Epithelial Sodium Channels; D006801:Humans; D017136:Ion Transport / Q000187:drug effects; D009297:Nasal Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015222:Sodium Channels / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000187:drug effects
C505032:CFTR protein, human; C492109:CLCA1 protein, human; D018118:Chloride Channels; D053503:Epithelial Sodium Channels; D015222:Sodium Channels; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D000584:Amiloride; D000255:Adenosine Triphosphate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D015056:1-Methyl-3-isobutylxanthine