The relation between ion permeation and recovery from inactivation of ShakerB K+ channels.
We have studied the relation between permeation and recovery from N-type or ball-and-chain inactivation of ShakerB K channels. The channels were expressed in the insect cell line Sf9, by infection with a recombinant baculovirus, and studied under whole cell patch clamp. Recovery from inactivation occurs in two phases. The faster of the two lasts for approximately 200 ms and is followed by a slow phase that may require seconds for completion. The fast phase is enhanced by both permeant ions (K+, Rb+) and by the blocking ion Cs+, whereas the impermeant ions (Na+, Tris+, choline+) are ineffective. The relative potencies are K+ > Rb+ > Cs+ > NH4+ >> Na+ approximately choline+ approximately Tris+. Ion permeation through the channels is not essential for recovery. The results suggest that cations influence the fast phase of recovery by binding in a site with an electrical distance greater than 0.5. Recovery from fast inactivation is voltage-dependent. With Na+, choline+, or Tris+ outside, about 15% of the channels recover in the fast phase (-80 mV), and the other 85% apparently enter a second inactivated state from which recovery is very slow. Recovery in this phase is not influenced by external ions, but is speeded by hyperpolarization.
Gómez-Lagunas
F
F
University of Pennsylvania, Department of Physiology, Philadelphia 19104-6085.
Armstrong
C M
CM
D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology; D002460:Cell Line; D002586:Cesium / Q000494:pharmacology; D015870:Gene Expression; D017136:Ion Transport; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D010539:Permeability; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D051637:Shaker Superfamily of Potassium Channels; D018411:Spodoptera
D002412:Cations; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D051637:Shaker Superfamily of Potassium Channels; D002586:Cesium; D002118:Calcium