An Improved Method For Real-Time Monitoring of Membrane Capacitance in Xenopus laevis Oocytes

Bernhard M. Schmitt, Hermann Koepsell
2002 Biophysical Journal  
Measurements of membrane capacitance (C m ) in Xenopus laevis oocytes offer unique experimental possibilities but are difficult to perform with current methods. To improve C m measurements in the two-electrode voltage clamp (TEVC) mode, we developed a paired-ramp protocol and tested its performance in a model circuit (with tunable C m , membrane resistance R m , and series resistance R s ) and in Xenopus oocytes. In the cell model and with R s ϭ 0 ⍀, inaccuracy of C m estimates was Ͻ1% under
more » ... ely varying conditions (R m ranging from 100 to 2000 k⍀, and C m from 50 to 1000 nF). With R s Ͼ 0 ⍀, C m was underestimated by a relative error ⑀ closely approximated as Ϸ 2 ϫ R s /(R s ϩ R m ), in keeping with the theoretical prediction. Thus, may be neglected under standard conditions or, under extreme conditions, corrected for if R s is known. Relative imprecision of C m estimates was small, independent of R s , and inversely related to C m (Ͻ1.5% at 50 nF, Ͻ0.4% at 200 nF). Averaging allowed reliable detection of C m deviations from 200 nF of 0.1 nF, i.e., 0.05%. In Xenopus oocytes, we could resolve C m changes that were small (e.g., ⌬C m Ϸ 2 nF upon 100 M 8-Br-cAMP), fast (e.g., ⌬C m /⌬t Ϸ 20nF/30s upon 1 M phorbol myristate acetate (PMA)) or extended and complex (e.g., fast increase, followed by prolonged C m decrease upon 1 M PMA). Rapidly alternating between paired ramps and a second, step protocol allowed quasi-simultaneous monitoring of additional electrical parameters such as R m , slope conductance g m , and reversal potential E rev . Taken together, our method is suited to monitor C m in Xenopus oocytes conveniently, with high temporal resolution, accuracy and precision, and in parallel with other electrical parameters. Thus, it may be useful for the study of endo-and exocytosis and of membrane protein regulation and for electrophysiological high-throughput screening.
doi:10.1016/s0006-3495(02)75490-8 pmid:11867451 pmcid:PMC1301937 fatcat:4bhpmcffmvgphmh577vfpi3wyi