TRANSEPITHELIAL VOLTAGE AND RESISTANCE OF VESTIBULAR DARK CELL EPITHELIUM FROM THE GERBIL AMPULLA

Transepithelial voltage (V-t) and resistance (R(t)) were measured across the dark cell epithelium of the gerbil ampulla using a micro Ussing chamber of improved design in order to test the view that the histologically similar epithelia in the utricle and in the ampullae exhibit similar electrophysiologic functions. V-t was found to be 8.0 +/- 0.3 mV and R(t) was 11.6 +/- 0.4 ohm-cm(2) (N = 179) when both sides of the tissue were perfused with symmetric perilymph-like solution. The equivalent short circuit current (I-sc = V-t/R(t)) was 712 +/- 18 mu A/cm(2) (N = 179). I-sc was reduced from 638 +/- 60 to 48 +/- 16 mu A/cm(2) (N = 14) by basolateral perfusion of 10(-3) M ouabain and from 538 +/- 27 to 27 +/- 4 mu A/cm(2) (N = 15) by basolateral perfusion of 5.10(-5) M bumetanide. Basolateral K+ steps (Na+ substitution) from 3.6 to 25 mM increased V-t from 6.5 +/- 0.5 to 12.2 +/- 0.6 mV and reduced R(t) from 9.7 +/- 0.7 to 7.4 +/- 0.5 ohm-cm(2) (N = 43). Apical K+ steps from 3.6 to 25, to 100 mM or to 145 mM led to a decrease in both V-t and R(t). The steady state V-t during apical perfusion of 145 mM K+ was near zero. Upon return to 3.6 mM K+, V-t transiently overshot its original level. Apical Cl- steps from 150 to 50 mM (gluconate substitution) monophasically decreased V-t from 5.9 +/- 0.7 to 4.1 +/- 0.8 mV (N 15) and increased R(t) from 9.6 +/- 1.3 to 12.0 +/- 1.5 ohm-cm(2) (N = 14). Apical perfusion of 5.10(-4) M DIDS increased V-t from 7.1 +/- 0.9 to a peak value of 11.9 +/- 1.7 mV (N = 6) and decreased R(t) from 10.2 +/- 2.1 to 9.0 +/- 1.7 ohm-cm(2) at the time of the peak V-t. The present results are qualitatively similar to data obtained in the utricle, suggesting a functional similarity between the dark cell epithelium in these two regions of the vestibular labyrinth. Further, the data support the hypothesis that the vestibular dark cells contribute a lumen-positive voltage only when the K+ concentration of endolymph falls below the level normally found in vivo.