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.
University of Pennsylvania, Department of Physiology, Philadelphia 19104-6085.
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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