title: The dynamic relationships between the three events that release individual Na⁺ ions from the Na⁺/K⁺-ATPase.
abstract: Na(+)/K(+) pumps move net charge through the cell membrane by mediating unequal exchange of intracellular Na(+) and extracellular K(+). Most charge moves during transitions that release Na(+) to the cell exterior. When pumps are constrained to bind and release only Na(+), a membrane voltage-step redistributes pumps among conformations with zero, one, two or three bound Na(+), thereby transiently generating current. By applying rapid voltage steps to squid giant axons, we previously identified three components in such transient currents, with distinct relaxation speeds: fast (which nearly parallels the voltage-jump time course), medium speed (τ(m)=0.2-0.5 ms) and slow (τ(s)=1-10 ms). Here we show that these three components are tightly correlated, both in their magnitudes and in the time courses of their changes. The correlations reveal the dynamics of the conformational rearrangements that release three Na(+) to the exterior (or sequester them into their binding sites) one at a time, in an obligatorily sequential manner.
authors.affiliation: Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA. gadsby@rockefeller.edu
authors.forename: David C
authors.initials: DC
authors.lastname: Gadsby
authors.forename: Francisco
authors.initials: F
authors.lastname: Bezanilla
authors.forename: Robert F
authors.initials: RF
authors.lastname: Rakowski
authors.forename: Paul
authors.initials: P
authors.lastname: De Weer
authors.forename: Miguel
authors.initials: M
authors.lastname: Holmgren
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D049832:Decapodiformes; D004594:Electrophysiology / Q000379:methods; D017136:Ion Transport; D007477:Ions; D008564:Membrane Potentials; D008954:Models, Biological; D012964:Sodium / Q000737:chemistry*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
chemical_list: D007477:Ions; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase