Transepithelial capacitance decrease reveals closure of lateral interspace in A6 epithelia

A sine wave method was used to measure transepithelial capacitance (C-T) at 4.1 kHz (C-T(HF)). Model calculations show that C-T(HF) reflects the equivalent capacitance of the series arrangement of apical and basolateral membrane capacitance. Cell swelling induced by reducing the basolateral osmolality from 260 to 140 mosmol/kg H2O (NaCl or sucrose removal) transiently decreased C-T(HF). The decrease in C-T(HF) (Delta C-T(HF)) reached its maximum 30 s after the onset of cell swelling and a complete recovery of C-T(HF) was attained within 3-4 min. Delta C-T(HF) could be diminished by manoeuvres that reduced the rate of amplitude of cell swelling, i.e. lowering the temperature or treatment with low concentrations of glutaraldehyde (0.025%). Delta C-T(HF) increased with the magnitude of the osmotic perturbation but saturated at large volume expansions. Delta C-T(HF) increased with culture time. Electron micrographs showed a clear correlation between time course of C-T(HF) changes and the closure of the lateral interspace (LIS). A striking correlation between the occurrence of C-T(HF) recovery and the ability of the cells to develop a regulatory volume decrease (RVD) was found: Gd3+ (0.5 mM) inhibited both phenomena. The frequency dependence of CT was obtained from impedance spectra recorded over the range of 4 Hz to 22 kHz. These data agree with model calculations in which the contribution of the access resistance to the lateral membrane was included. All observations are consistent with the idea that Delta C-T(HF) originates from the closure of the LIS during cell swelling. The latter phenomenon increases the access resistance to the lateral membrane, which results in a marked reduction of the basolateral membrane area detected at high frequencies with capacitance measurements.