title: The kinetics of the inhibition by dihydroouabain of the sodium pump current in single rabbit cardiac Purkinje cells.
abstract: The kinetics of the inhibition by dihydroouabain (DHO) of the Na pump current were studied in isolated rabbit cardiac Purkinje cells by means of whole-cell recording. A fast exchange of the extracellular solution at the membrane of the cell studied was performed via two multi-barrelled pipettes nearby. Judging from the steady-state inhibition of the Na pump current at various DHO concentrations half maximal inhibition occurred at 1 x 10(-5) mol/l DHO in a medium containing 2 mmol/l K+ and at 3.5 x 10(-5) mol/l DHO in a solution containing 10.8 mmol/l K+. Assuming a reversible one-to-one binding reaction, the time course of DHO binding and unbinding was analysed under a variety of conditions. It was shown that the antagonistic effect of K+ on the inhibition of the pump current was entirely due to a decrease of the association rate constant of DHO binding to the sodium pump at higher K+ concentrations. The association rate constant amounted to 1 x 10(4) (mol/l)-1.s-1 at 2 mmol/l K+ and to 2.8 x 10(3) (mol/l)-1.s-1 at 10.8 mmol/l K+. The dissociation rate constant of DHO unbinding remained unchanged (approximately 0.06 s-1). The equilibrium dissociation constant KD for the inhibition of the pump current by DHO decreased by a factor 3 to 5 if the Na+ concentration of the patch pipette solution was augmented from 5 to 50 mmol/l. Increasing DHO concentrations inhibited the pump current increasingly faster and to a larger extent. The KD values derived showed little variation with the concentration of DHO applied.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Interdisciplinary Research Centre, Catholic University of Leuven, Kortrijk, Belgium.
authors.forename: F V
authors.initials: FV
authors.lastname: Bielen
authors.forename: H G
authors.initials: HG
authors.lastname: Glitsch
authors.forename: F
authors.initials: F
authors.lastname: Verdonck
mesh_terms: D000818:Animals; D004594:Electrophysiology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects*
chemical_list: C000977:dihydroouabain; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium