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Neurosciences, Loeb Health Research Institute, Ottawa Hospital, Ottawa, Ontario, Canada K1Y 4E9
Mechanosensitive (MS) channels, ones whose open probability
varies with membrane tension in patch recordings, are diverse and
ubiquitous, yet many are remarkably insensitive to mechanical stimuli
in situ. Failure to elicit mechanocurrents from cells with abundant MS
channels suggests that, in situ, the channels are protected from
mechanical stimuli. To establish what conditions affect MS channel
gating, we monitored Lymnaea neuron
stretch-activated K (SAK) channels in cell-attached patches after
diverse treatments. Mechanosensitivity was gauged by rapidity of onset
and extent of channel activation during a step pressure applied to a
"naive" patch. The following treatments enhanced
mechanosensitivity: actin depolymerization (cytochalasin B),
N-ethylmaleimide, an inhibitor of
ATPases including myosin, elevated Ca (using A-23187), and osmotic
swelling (acutely and after 24 h). Osmotic shrinking decreased mechanosensitivity. A unifying interpretation is that traumatized cortical cytoskeleton cannot prevent transmission of mechanical stimuli
to plasma membrane channels. Mechanoprotection and capricious mechanosensitivity are impediments to cloning efforts with MS channels.
We demonstrate a potpourri of endogenous MS currents from
L-M(TK
) fibroblasts;
others had reported these cells to be MS current null and hence to be
suitable for expressing putative MS channels.
tension; actin; snail neuron; fibroblast
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