Stretch-activation and stretch-inactivation of Shaker-IR, a voltage-gated K+ channel.
Mechanosensitive (MS) ion channels are ubiquitous in eukaryotic cell types but baffling because of their contentious physiologies and diverse molecular identities. In some cellular contexts mechanically responsive ion channels are undoubtedly mechanosensory transducers, but it does not follow that all MS channels are mechanotransducers. Here we demonstrate, for an archetypical voltage-gated channel (Shaker-IR; inactivation-removed), robust MS channel behavior. In oocyte patches subjected to stretch, Shaker-IR exhibits both stretch-activation (SA) and stretch-inactivation (SI). SA is seen when prestretch P(open) (set by voltage) is low, and SI is seen when it is high. The stretch effects occur in cell-attached and excised patches at both macroscopic and single-channel levels. Were one ignorant of this particular MS channel's identity, one might propose it had been designed as a sophisticated reporter of bilayer tension. Knowing Shaker-IR's provenance and biology, however, such a suggestion would be absurd. We argue that the MS responses of Shaker-IR reflect not overlooked "mechano-gating" specializations of Shaker, but a common property of multiconformation membrane proteins: inherent susceptibility to bilayer tension. The molecular diversity of MS channels indicates that susceptibility to bilayer tension is hard to design out of dynamic membrane proteins. Presumably the cost of being insusceptible to bilayer tension often outweighs the benefits, especially where the in situ milieu of channels can provide mechanoprotection.
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Department of Medicine, University of Ottawa, Neurosciences, Ottawa Health Research Institute, The Ottawa Hospital, Ottawa, Ontario K1Y 4K9, Canada.
Juranka
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Morris
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D000818:Animals; D016477:Artifacts; D001274:Atmospheric Pressure; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004548:Elasticity; D004553:Electric Conductivity; D005682:Gadolinium / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011489:Protein Denaturation; D020673:Protein Renaturation; D051637:Shaker Superfamily of Potassium Channels; D014982:Xenopus laevis
D015221:Potassium Channels; D051637:Shaker Superfamily of Potassium Channels; D005682:Gadolinium