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Li fluxes reveal presence of Na‐Cl Cotransport (NCC) in Human Lens Epithelial Cells (LECs)
Author(s) -
Adragorma Cristina,
Chimote Ameet A.,
Lauf Peter K.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.936.5
Subject(s) - chemistry , bumetanide , cotransporter , ouabain , amiloride , furosemide , analytical chemistry (journal) , sodium , nuclear chemistry , chromatography , organic chemistry
Na‐K‐2Cl cotransport (NKCC) moves RbCl/KCl+NaCl/LiCl and, in FHL124 LECs, is not inhibited by hypotonicity. Here, we studied Li fluxes through NKCC in hyposmotic high K media and Rb fluxes in hyposmotic high Na to understand this effect. Li and Rb uptake were measured by atomic absorption spectrophotometry to determine LiKCC or NRbCC through bumetanide‐sensitive (BS) and Cl‐dependent fluxes in Na/K or Na‐free/K‐free (N‐methyl‐D‐glucamine) and Cl or Cl‐free (sulfamate or nitrate) media ± ouabain (O) or [O+B], ± thiazides, at varying Rb, Li or Cl molar fractions (MF). Main findings are: Li influx in isosmotic (300 mOsM) K was 1/3 of Rb influx in Na, and was mainly mediated by a Cl‐dependent Li flux (LiKCC). In 200 mOsM high K, LiKCC was abolished, whereas in high Na, NRbCC remained active. LiKCC and BS‐Li influx (BS‐LiKCC) showed bell‐shape curves for 0.1–1 Li MF, maxing at ∼0.6 MF. BS‐LiKCC was ¼ of LiKCC. The difference, i.e. the B‐insensitive/Cl‐dependent‐Li influx, saturated with Li and Cl MFs. K ms for Li were 11 with and 7–8 mM without external K, respectively; and ∼40 mM for Cl. Neither furosemide (<100 μM) nor thiazide derivatives inhibited LiCC. RTPCR, Western blots and immunochemistry revealed NCC RNA and protein, with NCC‐specific antibodies, besides the expected NKCC1. Thus, a K‐independent/Cl‐dependent Li flux (LiCC) revealed the presence of NCC in FHL124 LECs.