Membrane admittance of cloned muscle cells in culture: use of a micropipet technique

Abstract

The impedance characteristics of muscle cells have been investigated by many investigators because of its unique features. The studies of the electrical properties of cloned cultured muscle cells, however, are scant and only a handful of papers have been published. In this report, the admittance of cultured Myoblast L6 cells was investigated. The capacitance and conductance of mononucleate myoblast cell membrane were found to be 2.2–2.5 μF/cm² and 50–60 μS/cm² and independent of frequency. The capacitance of 2.2 μF/cm² is larger than the widely accepted capacitance value for most of the biological cell membranes, i.e., 1 μF/cm². In contrast, those found for fused multinucleate myotubes are 5–6 μF/cm² and 0.4 mS/cm² and exhibited a marked frequency dependence. We postulate that the large and frequency dependent capacitance of myotubes does not arise from the surface membrane alone but is due to a tubule-like structure which may be similar to those found in frog muscles. Analysis of the results using an equivalent circuit demonstrates that the capacitance of myotubes is independent of frequency when the correction is made for the series resistances which are distributed in the lumen of tubule-like structure. An alternative explanation for the frequency dependent capacitance is based on the use of the transmission line theory or cable equation. The cable theory predicts that measured capacitance and conductance are inherently a function of frequency regardless of the nature of membrane capacitance and conductance if the dimension of cells is larger than or comparable to the propagation constant.