title: K⁺ channel gating: C-type inactivation is enhanced by calcium or lanthanum outside.
abstract: Many voltage-gated K(+) channels exhibit C-type inactivation. This typically slow process has been hypothesized to result from dilation of the outer-most ring of the carbonyls in the selectivity filter, destroying this ring's ability to bind K(+) with high affinity. We report here strong enhancement of C-type inactivation upon extracellular addition of 10-40 mM Ca(2+) or 5-50 µM La(3+). These multivalent cations mildly increase the rate of C-type inactivation during depolarization and markedly promote inactivation and/or suppress recovery when membrane voltage (V(m)) is at resting levels (-80 to -100 mV). At -80 mV with 40 mM Ca(2+) and 0 mM K(+) externally, ShBΔN channels with the mutation T449A inactivate almost completely within 2 min or less with no pulsing. This behavior is observed only in those mutants that show C-type inactivation on depolarization and is distinct from the effects of Ca(2+) and La(3+) on activation (opening and closing of the V(m)-controlled gate), i.e., slower activation of K(+) channels and a positive shift of the mid-voltage of activation. The Ca(2+)/La(3+) effects on C-type inactivation are antagonized by extracellular K(+) in the low millimolar range. This, together with the known ability of Ca(2+) and La(3+) to block inward current through K(+) channels at negative voltage, strongly suggests that Ca(2+)/La(3+) acts at the outer mouth of the selectivity filter. We propose that at -80 mV, Ca(2+) or La(3+) ions compete effectively with K(+) at the channel's outer mouth and prevent K(+) from stabilizing the filter's outer carbonyl ring.
authors.affiliation: Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104 carmstro@mail.med.upenn.edu.
authors.forename: Clay M
authors.initials: CM
authors.lastname: Armstrong
authors.affiliation: Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hoshi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D045744:Cell Line, Tumor; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D007811:Lanthanum / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D051637:Shaker Superfamily of Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D026902:Potassium Channel Blockers; D051637:Shaker Superfamily of Potassium Channels; D007811:Lanthanum; D002118:Calcium