Fig. 2: XPR1 exhibits voltage- and Pi-dependent ion channel activity and Pi transport.
From: The identification of XPR1 as a voltage- and phosphate-activated phosphate-permeable ion channel
a Inwardly-rectifying currents evoked from an excised GUV patch with hXPR1 by voltage ramps (−105 mV to +75 mV) from +15 mV. b Inward currents are evoked by hyperpolarizing voltage-pulses (−15 to −105 mV, in 10 mV intervals) from +95 mV in a GUV patch with hXPR1, but not in detergent control. c Outward tail current at +15 mV following 1 s hyperpolarizing pulses. d Normalized hXPR1 G-V relation from tail currents (mean ± SEM, n = 3 replicates from one GUV) fit by a Boltzmann function (z = −1.8 ± 0.2 e, V1/2 = −34 ± 2 mV, mean ± SD). e Unitary current activity during voltage ramps or +40 mV pulses from a HEK293S GnTI- cell expressing hXPR1. a–e were from inside-out patches with external 0 Pi NMDG-MSA and internal 20 Pi, 0.07 Ca2+, K-MSA solutions. f Unitary XPR1 current recorded from HEK293 cell with single open level and associated all-points histogram at −50 mV with external 1 Pi NMDG-citrate and internal 20 Pi, 0.07 Ca2+, K-MSA solutions. g XPR1 currents evoked from a GUV patch by voltage ramps with 75 mM Pi as the sole internal anion (black) or with 75 mM Pi + 10 Cl− (red) are superimposable. XPR1 currents evoked from a GUV patch by voltage ramps (h) or –50 mV pulses (i) are enhanced as internal Pi is increased from 10 mM (blue) to 75 mM (red), and almost undetectable in 0 Pi (black) using internal 10 Cl K-MSA with external 0 Pi NMDG-MSA solutions. Thick curves represent an average of 5 (g) or 10 (h, i) traces (thin curves). j G-V relations in 10 and 75 mM Pi (mean±SEM, n = 3 patches). G-Vs at both [Pi] were normalized to the maximal conductance in 75 mM Pi. k Schematics of the [32P] Pi transport assay with proteoliposomes. A membrane voltage potential difference was generated using a potassium gradient and valinomycin. l Time-dependent accumulation (mean±SEM, n = 6 independent assays) of [32P] Pi in hXPR1-containing proteoliposomes without valinomycin (blue), with valinomycin (red), and in empty liposomes with valinomycin (black) as control.
