ABSTRACT
Cholesterol promotes basal and verapamil-induced ATPase activity of P-glycoprotein (P-gp). We investigated whether these effects are related to each other and to the impact of the sterol on bilayer fluidity and verapamil membrane affinity. P-gp was reconstituted in egg-phosphatidylcholine (PhC) liposomes with or without cholesterol, 1,2-dipalmitoyl-phosphatidylcholine (DPPC), alpha-tocopherol (alpha-Toc) or 2,2,5,7,8-pentamethyl-6-chromanol (PMC). Basal and verapamil-induced ATPase activities were studied with an enzymatic assay. Membrane fluidity was characterized with diphenyl-hexatriene anisotropy measurements and membrane affinity by equilibrium dialysis. DPPC (70% mol/mol) decreased the fluidity of PhC bilayers to the same level as 20% cholesterol. PMC (20%) and alpha-Toc (20%) decreased the fluidity to lesser extents. alpha-Toc and PMC, but not DPPC increased the verapamil membrane affinity. While 20% cholesterol strikingly enhanced the basal ATPase activity, none of the other constituents had a similar effect. In contrast, verapamil stimulation of P-gp ATPase activity was not only enabled by cholesterol but also by alpha-Toc and DPPC. PMC had no effect. In conclusion, cholesterol exerts distinct effects on basal and verapamil-induced ATPase activity. The influence on basal ATPase activity is sterol-specific while its effect on verapamil-induced ATPase activity is unspecific and not related to its influence on membrane fluidity and on verapamil membrane affinity.
Subject(s)
ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , Adenosine Triphosphatases/biosynthesis , Adenosine Triphosphatases/metabolism , Cholesterol/physiology , 1,2-Dipalmitoylphosphatidylcholine , ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry , ATP Binding Cassette Transporter, Subfamily B, Member 1/isolation & purification , Adrenergic alpha-Agonists/pharmacology , Animals , Anisotropy , Antineoplastic Agents, Phytogenic/pharmacology , Calcium Channel Blockers/pharmacology , Cell Line, Tumor , Enzyme Induction/drug effects , Excipients , Lipid Bilayers , Liposomes/chemistry , Membranes, Artificial , Mice , Propanolamines/pharmacology , Verapamil/pharmacology , Vinblastine/pharmacology , alpha-Tocopherol/chemistryABSTRACT
Involvement of the sternocostal joints was investigated in a series of 46 males and 18 females following median sternotomy annually in a 5-year period and compared to 62 age- and sex matched control subjects after one year solely. Both groups had a mean age of 49.2 years. The degenerative chondroarthropathy of sternocostal joints was 1.69-times more frequent in heart operated upon patients as compared to control persons. Based on radiographic findings the degenerative chondroarthropathies were classed in 0 to 3 severity groups. Were seen articular space narrowing in 95.4%, osteophytes of the margin of the articular surface in 88%, subchondral bony eburnation in 79% and cystic radiolucencies in 48.9% of sternocostal joints on poststernotomy standard plain film tomograms. Not occurred intraarticular gas phenomenon and bony ankylosis. The development of arthropathies is traced back to mechanical stress-related predisposing factors and stressed the importance of oculoneutral dehiscences that simulated normal roentgenanatomic projections and caused a masked insufficiency in sternocostal junctions.