title: Capsazepine, a synthetic vanilloid that converts the Na,K-ATPase to Na-ATPase.
abstract: Capsazepine (CPZ), a synthetic capsaicin analogue, inhibits ATP hydrolysis by Na,K-ATPase in the presence but not in the absence of K(+). Studies with purified membranes revealed that CPZ reduced Na(+)-dependent phosphorylation by interference with Na(+) binding from the intracellular side of the membrane. Kinetic analyses showed that CPZ stabilized an enzyme species that constitutively occluded K(+). Low-affinity ATP interaction with the enzyme was strongly reduced after CPZ treatment; in contrast, indirectly measured interaction with ADP was much increased, which suggests that composite regulatory communication with nucleotides takes place during turnover. Studies with lipid vesicles revealed that CPZ reduced ATP-dependent digitoxigenin-sensitive (22)Na(+) influx into K(+)-loaded vesicles only at saturating ATP concentrations. The drug apparently abolishes the regulatory effect of ATP on the pump. Drawing on previous homology modeling studies of Na,K-ATPase to atomic models of sarcoplasmic reticulum Ca-ATPase and on kinetic data, we propose that CPZ uncouples an Na(+) cycle from an Na(+)/K(+) cycle in the pump. The Na(+) cycle possibly involves transport through the recently characterized Na(+)-specific site. A shift to such an uncoupled mode is believed to produce pumps mediating uncoupled Na(+) efflux by modifying the transport stoichiometry of single pump units.
authors.affiliation: Institute of Physiology and Biophysics, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Yasser A
authors.initials: YA
authors.lastname: Mahmmoud
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry*; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D002211:Capsaicin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000737:chemistry*; D002414:Cations, Monovalent / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D012964:Sodium / Q000737:chemistry; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000737:chemistry
chemical_list: D027682:Cation Transport Proteins; D002414:Cations, Monovalent; D008024:Ligands; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D000254:Sodium-Potassium-Exchanging ATPase; C071423:capsazepine; D002211:Capsaicin