Overview

K-selective voltage-gated channels (Kv) are multi-conformation bilayer-embedded proteins whose mechanosensitive (MS) Popen(V) implies that at least one conformational transition requires the restructuring of the channel-bilayer interface. Unlike Morris and colleagues, who attributed MS-Kv responses to a cooperative V-dependent closed-closed expan-sion$compaction transition near the open state, Mackinnon and colleagues invoke expan-sion during a V-independent closed$open transition. With increasing membrane tension, they suggest, the closed$open equilibrium constant, L, can increase>100-fold, thereby taking steady-state Popen from 0!1; “exquisite sensitivity to small...mechanical perturba-tions”, they state, makes a Kv “as much a mechanosensitive...as...a voltage-dependent channel”. Devised to explain successive gK(V) curves in excised patches where tension spontaneously increased until lysis, their L-based model falters in part because of an over-looked IK feature; with recovery from slow inactivation factored in, their g(V) datasets are fully explained by the earlier model (a MS V-dependent closed-closed transition, invariant L4). An L-based MS-Kv predicts neither known Kv time courses nor the distinctive MS re-sponses of Kv-ILT. It predicts Kv densities (hence gating charge per V-sensor) several-fold different from established values. If opening depended on elevated tension (L-based model), standard gK(V) operation would be compromised by animal cells’membrane flaccid-ity. A MS V-dependent transition is, by contrast, unproblematic on all counts. Since these is-sues bear directly on recent findings that mechanically-modulated Kv channels subtly tune pain-related excitability in peripheral mechanoreceptor neurons we undertook excitability modeling (evoked action potentials). Kvs with MS V-dependent closed-closed transitions produce nuanced mechanically-modulated excitability whereas an L-based MS-Kv yields extreme, possibly excessive (physiologically-speaking) inhibition