Isolated supporting cells from the organ of Corti: Some whole cell electrical characteristics and estimates of gap junctional conductance

Whole cell voltage clamp studies were performed upon isolated and small groups of supporting cells from the guinea pig organ of Corti in order to evaluate junctional and non-junctional membrane characteristics. Single Hensen cells have an average input resistance and capacitance of 1.03 G omega and 24.9 pF, respectively. I-V functions indicate an outward K+ rectification, which is blocked by external TEA, intracellular Cs, or photo-irradiation of intracellularly injected fluorescent dye. Voltage clamping of pairs or small groups of cells indicates that supporting cells 'share' K+ channels within the syncitium. The input impedance of coupled cells was studied during uncoupling with CO2 or octanol media. As expected, coupled cells showed an increase in input capacitance and a decrease in input resistance over single cell values. Input capacitance is a more sensitive indicator of cell coupling than dc input resistance. During uncoupling, input capacitance values drop to single cell levels prior to an increase of dc input resistance to single cell levels. Modeling the results indicates that Hensen cells are well-coupled under normal conditions and may have junctional resistances with values less than 0.1% of the non-junctional resistance. The sensitivity of the supporting cell syncitium's input impedance to small changes in junctional resistance markedly influences the syncitium's RC filter characteristics, and thus may control the frequency response of sound evoked electrical activity measurable in supporting cells in vivo.