Electrical properties of the otic vesicle epithelium in the chick embryo

The electrophysiological properties of the epithelium of the otic vesicle were studied in the chick embryo using conventional microelectrode techniques. A preparation is described that allows continuous recording of transmural potential and resistance during changes in the composition of the bathing fluid. Vesicles in stages 18 to 22 showed a spontaneous transmural potential (ET) that ranged from 2 to 6 mV, inner positive. This electrical potential difference was abolished after 2 h incubation in K+-free strophantidin (10(-4) M) and it increased by about twofold immediately after addition of the cation ionophore Amphotericin B (250 microM) to the bath. The specific resistance of the wall (RT) was about 80 omega cm2 between stages 18 and 22 indicating a low-resistance, noncellular, permeation pathway for current flow. The short-circuit current, calculated from ET and RT was about 50 X 10(-6) A cm-2 throughout this period. This corresponds to a net flux of 187 X 10(-8) mol cm-2 h-1 of a single cation pumped towards the towards the vesicular cavity. Diffusion potentials (salt gradients and single-ion substitutions) showed a selectivity ratio PK:PNa:PCl = 1:0.9:0.7, which is that of a weakly charged aqueous pathway. Measurements of vesicular volume and surface area showed an increase by a factor of ten in the size of the vesicle with maximal rates of change in volume of 5 microliter cm-2 h-1. The electrical properties reported here for the epithelium of the otic vesicle resemble very much those of 'leaky' epithelia which are known to transport ions and water at a very high rate.