Voltage-dependent capacitance of human embryonic kidney cells

Abstract

We determine membrane capacitance, C as a function of dc voltage for the human embryonic kidney (HEK) cell. C was calculated from the admittance, Y, obtained during a voltage ramp when the HEK cell was held in whole-cell patch-clamp configuration. Y was determined at frequencies of 390.625 and 781.25 Hz from the measured current, i obtained with a dual-sinusoidal stimulus. We find that the fractional increase in the capacitance, C is small (<1%) and grows with the square of the voltage, Ψ. C can be described by: [where C(0): Capacitance at 0 volts, ψ s : Difference in surface potential between cytoplasmic and extracellular leaflets and α: Proportionality constant]. We find that α and ψ s are 0.120 (±0.01) V −2 and −0.073 (±0.017) V in solutions that contain ion channel blockers and 0.108 (±0.29) V −2 and −0.023 (±0.009) V when 10 mM sodium salicylate was added to the extracellular solution. This suggests that salicylate does not affect the rate at which C grows with Ψ, but reduces the charge asymmetry of the membrane. We also observe an additional linear differential capacitance of about (−46 fFV −1 ) in about 60% of the cells, this additional component acts simultaneously with the quadratic component and was not observed when salicylate was added to the solution. We suggest that the voltage dependent capacitance originates from electromechanical coupling either by electrostriction and/or Maxwell stress effects and estimate that a small electromechanical force (≈1 pN) acts at physiological potentials. These results are relevant to understand the electromechanical coupling in outer hair cells (OHCs) of the mammalian cochlea, where an asymmetric bell-shaped C versus Ψ relationship is observed upon application of a similar field. Prestin, a membrane protein expressed in OHCs is required to observe this function. When we compare the total charge contributions from HEK cell membrane (7×10 4 electrons, 10 pF cell) with that determined for prestin transfected cells (up to 5×10 6 electrons) we conclude that the charge contributions from the collective motion of membrane proteins and lipids in the field is dwarfed relative to that when prestin is present. We suggest that the capacitance-voltage relationships should be similar to that observed for HEK cells for OHCs that do not express prestin in their membranes.

Molecular Dynamics Simulations of Salicylate Effects on the Micro- and Mesoscopic Properties of a Dipalmitoylphosphatidylcholine Bilayer

“…For the simulated systems with NaCl, only 60mM salicylate caused a significant increase (p < 0.05) in the electrostatic potential at the water-lipid interface. This increase is in qualitative agreement with experiments demonstrating salicylate-induced changes in membrane potentials (17,72) and surface charges (15) for human embryonic kidney (HEK) cells as well as various types of neurons (73)(74)(75)(76).…”

“…OHCs play an important role in the sensitivity of mammalian hearing for high-frequency sounds through a mechanism of electromechanical feedback (12). While the exact molecular mechanism of salicylate's effect on OHC electromechanical response is still unknown, experimental work has suggested that salicylate may interact with several components of the OHC, including the phospholipid bilayer (13)(14)(15)(16)(17)(18)(19)(20) and membrane-bound proteins such as prestin (21)(22)(23). In this study, we have investigated one aspect of salicylate's effects on OHC electromechanical coupling: the perturbation of electrical and mechanical biomembrane properties by salicylate in the absence cytoskeletal components or membrane-bound motor proteins such as prestin.…”

Millisecond infrared laser pulses depolarize and elicit action potentials on in-vitro dorsal root ganglion neurons

“…Further experiments include the measurements of the currents in voltage-clamped configuration. Membrane capacitance of DRG neurons is 12 pF [36] while it is 26 pF for C elegans [17], 200 nF for oocyte [37] and 7 to 8 pF for HEK [38]. Since membrane capacitances from DRG neurons and HEK cells are similar, it is unlikely that this parameter alone is the key value for the decrease of dT/dt observed in our work.…”

Essential Helix Interactions in the Anion Transporter Domain of Prestin Revealed by Evolutionary Trace Analysis

“…Electrophysiological data were obtained from cells using the whole-cell voltage-clamp technique. Our recording techniques are fully described previously (Farrell et al, 2006); a brief description follows. Culture dishes containing transfected cells were placed on the stage of an inverted microscope (Zeiss, Gottingen, Germany).…”