Shaker IR T449 mutants separate C- from U-type inactivation.
Previous studies demonstrated that slow inactivation of the Shaker potassium channel can be made ~100-fold faster or slower by point mutations at a site in the outer pore (T449). However, the discovery that two forms of slow inactivation coexist in Shaker raises the question of which inactivation process is affected by mutation. Equivalent mutations in K(V)2.1, a channel exhibiting only U-type inactivation, have minimal effects on inactivation, suggesting that mutation of Shaker T449 acts on C-type inactivation alone, a widely held yet untested hypothesis. This study reexamines mutations at Shaker T449, confirming that T449A speeds inactivation and T449Y/V slow it. T449Y and T449V exhibit U-type inactivation that is enhanced by high extracellular potassium, in contrast to C-type inactivation in T449A which is inhibited by high potassium. Automated parameter estimation for a 12-state Markov model suggests that U-type inactivation occurs mainly from closed states upon weak depolarization, but primarily from the open state at positive voltages. The model also suggests that WT channels, which in this study exhibit mostly C-type inactivation, recover from inactivation through closed-inactivated states, producing voltage-dependent recovery. This suggests that both C-type and U-type inactivation involve both open-inactivated and closed-inactivated states.
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106, USA.
Quentin
Q
Jamieson
Stephen W
SW
Jones
D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008390:Markov Chains; D008564:Membrane Potentials; D008958:Models, Molecular; D020125:Mutation, Missense; D010641:Phenotype; D011188:Potassium / Q000502:physiology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051669:Shab Potassium Channels / Q000235:genetics* / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology
D026902:Potassium Channel Blockers; D051669:Shab Potassium Channels; D019789:Tetraethylammonium; D011188:Potassium