The AC impedance of Necturus gallbladder epithelium.

The impedance of Necturus gallbladder epithelium was determined using sine wave currents of 1 Hz to 30 kHz. In control Ringer's solution the impedance locus exhibited a simple semicircle with minute shift of the high frequency end along the real axis and a minute depression of the center below the real axis (average 0.9 +/- 0.7 degrees). Neglecting the slight suppression, the impedance of 1 cm2 of epithelium can be represented by an electrical analogue consisting of a parallel RC element of 115 +/- 26 omega and 5.16 +/- 0.9 muF in series with a small resistor of 5.3 +/- 1.3 omega. In agreement with experimental results obtained under ionic or osmotic substitutions, the applicability of this simple RC analogue to gallbladder epithelium under control conditions can be explained by the influence of the paracellular shunt and by assuming the time constants of the apical and basal cell membranes to be comparable. Based on these data and on voltage divider measurements obtained with microelectrodes the capacitances of the apical and basal cell membrane can be estimated to be approximately 7 and approximately 18 muF/cm2. The latter value agrees well with estimates of the surface folding obtained from electromicrographs, if the specific cell membrane capacitance is assumed to be approximately 1 muF/cm2 as in other cell membranes.