Effects of membrane potential and tension on prestin, the outer hair cell lateral membrane motor protein

1. Under whole-cell voltage clamp, the effects of initial voltage condition s and membrane tension on gating charge and voltage-dependent capacitance w ere studied in human embryonic kidney cells (TSA201 cell line) transiently transfected with the gene encoding the gerbil protein prestin. Conformation al changes in this membrane-bound protein probably provide the molecular ba sis of the outer hair cell (OHC) voltage-driven mechanical activity, which spans the audio spectrum. 2. Boltzmann characteristics of the charge movement in transfected cells we re similar to those reported for OHC's (Q(max) = 0.99 +/- 0.16 pC, z = 0.88 +/- 0.02; n = 5, means + S.E.M.). Unlike that of the adult OHC, the voltag e at peak capacitance (V-pkem) was very negative (-74.7 +/- 3.8 mV). Linear capacitance in transfected cells was 43.7 +/- 13.8 pF and membrane resista nce was 458 +/- 123 M Omega. 3. Voltage steps front the holding potential preceding the measurement of c apacitance-voltage functions caused a time- and voltage-dependent shift in V-pkem. For a prepulse to -150 mV, from a holding potential of 0 mV, V-pkem shifted 6.4 mV, and was fitted by a single exponential time constant of 45 ms. A higher revolution analysis of this time course was made by measuring the change in capacitance during a fixed voltage step and indicated a doub le exponential shift (tau (ll) = 51.6 ms, tau (l) = 8.5 s) similar to that of the native gerbil OHC. 4. Membrane tension, delivered by increasing pipette pressure, caused a pos itive shift in V-pkem. A maximal shift of 7.5 mV was obtained with 2 kPa of pressure. The effect was reversible. 5. Our results show that the sensitivity of prestin to initial voltage and membrane tension, though present, is less than that observed in adult OHCs. It remains possible that some other interacting molecular species within t he lateral plasma membrane of the native OHC amplifies the effect of tensio n and prior voltage on prestin's activity.