ABSTRACT
Previous studies suggested that four transmembrane domains 5, 6, 11, 12 make the greatest contribution to forming the pore of the CFTR chloride channel. We used excised, inside-out patches from oocytes expressing CFTR with alanine-scanning mutagenesis in amino acids in TM6 and TM12 to probe CFTR pore structure with four blockers: glibenclamide (Glyb), glipizide (Glip), tolbutamide (Tolb), and Meglitinide. Glyb and Glip blocked wildtype (WT)-CFTR in a voltage-, time-, and concentration-dependent manner. At V (M) = -120 mV with symmetrical 150 mM Cl(-) solution, fractional block of WT-CFTR by 50 µM Glyb and 200 µM Glip was 0.64 ± 0.03 (n = 7) and 0.48 ± 0.02 (n = 7), respectively. The major effects on block by Glyb and Glip were found with mutations at F337, S341, I344, M348, and V350 of TM6. Under similar conditions, fractional block of WT-CFTR by 300 µM Tolb was 0.40 ± 0.04. Unlike Glyb, Glip, and Meglitinide, block by Tolb lacked time-dependence (n = 7). We then tested the effects of alanine mutations in TM12 on block by Glyb and Glip; the major effects were found at N1138, T1142, V1147, N1148, S1149, S1150, I1151, and D1152. From these experiments, we infer that amino acids F337, S341, I344, M348, and V350 of TM6 face the pore when the channel is in the open state, while the amino acids of TM12 make less important contributions to pore function. These data also suggest that the region between F337 and S341 forms the narrow part of the CFTR pore.
Subject(s)
Cystic Fibrosis Transmembrane Conductance Regulator/drug effects , Sulfonylurea Compounds/pharmacology , Alanine/genetics , Amino Acid Sequence , Animals , Benzamides/pharmacology , Cystic Fibrosis Transmembrane Conductance Regulator/genetics , Cystic Fibrosis Transmembrane Conductance Regulator/metabolism , Glipizide/pharmacology , Glyburide/pharmacology , Ion Channel Gating/drug effects , Kinetics , Mutagenesis , Oocytes , Patch-Clamp Techniques , Tolbutamide/pharmacology , XenopusABSTRACT
Dislocation of the rotator platform in mobile-bearing total knee arthroplasty is a well-documented, albeit uncommon, phenomenon. A review of the literature has revealed multiple case reports describing spin out to 90° or complete extrusion of the polyethylene component. Closed reduction may be attempted in the acute presentation followed by revision if instability persists. We present a case of a 57-year-old woman who had a partial rotatory subluxation of her polyethylene component and underwent closed reduction resulting in a full 180° spinout. To our knowledge, this has not been described in the literature and should be considered as a possibility after closed reduction attempts. She was treated successfully with open exploration and poly exchange using a larger component.
