Figure 2.

Use of Xenopus oocyte cell-attached patch recordings to study MS gating in VGCs. (A) Endogenous “stretch-activated cation channel” activity and heterologously expressed Kv channels (Shaker, fast inactivation removed) exhibiting what a naive observer could reasonably construe to be “stretch-activated K channel” activity. In reality it is stretch-modulated VGC current (Gu et al., 2001). (B) A Xenopus oocyte, and a cartoon of pipette aspiration as used for applying membrane stretch (inset, a cell-attached macropatch; typically, smaller patches are used but this allows for visualization of non-traumatized plasma membrane; inset is modified from Shcherbatko et al., 1999). As explained in refs (Morris et al., 2006) and (Wang et al., 2009), membrane trauma, when it happens, is submicroscopic. (C) During pipette aspiration, stretch increases membrane tension, and does so whether aspiration pressure is negative (“suck”) or positive (“blow”), as seen for two very different VGCs, a Kv3 homotetramer and a Nav1.5 pseudotetramer. Multivalent lanthanide ions included in the pipette inhibit endogenous stretch channel activity (and, as expected, right-shift VGC currents by tens of mV). Here, and throughout, black, red, gray traces signify before, during, after stretch. (Di,ii) Illustrates “stretch difference currents” obtained from before/during/after records (two step depolarizations and one ramp depolarization are used here) and demonstrates that the magnitude of the stretch difference currents increase with increasing stretch intensity, while (iii) shows that stretch increases unitary K currents frequency at 0 mV (which corresponds to the reversal potential of endogenous stretch-activated cation channels). These figures are modified from (Gu et al., 2001; Laitko et al., 2006; Morris and Juranka, 2007a).