title: Shab K (+) channel slow inactivation: a test for U-type inactivation and a hypothesis regarding K (+) -facilitated inactivation mechanisms.
abstract: Herein, we report the first characterization of Shab slow inactivation. Open Shab channels inactivate within seconds, with two voltage-independent time constants. Additionally, Shab presents significant closed-state inactivation. We found that with short depolarizing pulses, shorter than the slowest inactivation time constant, the resulting inactivation curve has a marked U-shape, but as pulse duration increases, approaching steady-state conditions, the U-shape vanishes, and the resulting inactivation curves converge to the classical Boltzmann h∞ curve. Regarding the mechanism of inactivation, we found that external K (+) and TEA facilitate both open- and closed-state inactivation, while the cavity blocker quinidine hinders inactivation. These results together with our previous observations regarding the K (+) -dependent stability of the K (+) conductance, suggest the novel hypothesis that inactivation of Shab channels, and possibly that of other Kv channels whose inactivation is facilitated by K (+) , does not involve a significant narrowing of the extracellular entry of the pore. Instead, we hypothesize that there is only a rearrangement of a more internal segment of the pore that affects the central cavity and halts K (+) conduction.
authors: Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México UNAM, México, D F México.
authors: Elisa
authors: E
authors: Carrillo
authors: Imilla I
authors: II
authors: Arias-Olguín
authors: León D
authors: LD
authors: Islas
authors: Froylan
authors: F
authors: Gómez-Lagunas
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D004331:Drosophila melanogaster / Q000737:chemistry / Q000502:physiology; D015640:Ion Channel Gating; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011802:Quinidine / Q000494:pharmacology; D061987:Sf9 Cells; D051669:Shab Potassium Channels / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D018411:Spodoptera; D019789:Tetraethylammonium / Q000494:pharmacology
chemical_list: D029721:Drosophila Proteins; D026902:Potassium Channel Blockers; D051669:Shab Potassium Channels; C064033:Shab protein, Drosophila; D019789:Tetraethylammonium; D011802:Quinidine; D011188:Potassium
keywords: C-type inactivation; Drosophila; Shab; U-type inactivation; potassium channels; slow inactivation