Voltage-dependent sodium channel function is regulated through membrane mechanics

Cut-open recordings from Xenopus oocytes expressing either nerve (PN1) or s keletal muscle (SkM1) Na+ channel alpha subunits revealed slow inactivation onset and recovery kinetics of inward current. In contrast, recordings usi ng the macropatch configuration resulted in an immediate negative shift in the voltage-dependence of inactivation and activation, as well as time-depe ndent shifts in kinetics when compared to cut-open recordings. Specifically , a slow transition from predominantly slow onset and recovery to exclusive ly fast onset and fast recovery from inactivation occurred. The shift to fa st inactivation was accelerated by patch excision and by agents that disrup ted microtubule formation. Application of positive pressure to cell-attache d macropatch electrodes prevented the shift in kinetics, while negative pre ssure led to an abrupt shift to fast inactivation. Simultaneous electrophys iological recording and video imaging of the cell-attached patch membrane r evealed that the pressure-induced shift to fast inactivation coincided with rupture of sites of membrane attachment to cytoskeleton. These findings ra ise the possibility that the negative shift in voltage-dependence and the f ast kinetics observed normally for endogenous Na+ channels involve mechanic al destabilization. Our observation that the beta 1 subunit causes similar changes in function of the Na+ channel alpha subunit suggests that beta 1 m ay act through interaction with cytoskeleton.