Characteristics of voltage-dependent conductance in the membranes of a non-excitable tissue: the amphibian lens.

1. The electrical conductance of the frog lens membranes was observed to increase when the lens was depolarized by current, and to decrease when the lens was hyperpolarized. 2. The total lens conductance (GT) could be described by a voltage-dependent component (GH) together with a voltage-insensitive component (GO). 3. Conductance measured at the resting potential increased from 9.7 to 14.4 x 10(-5) S when the lens was depolarized by 9.1 mV in 10(-4) M-ouabain. The increase of conductance could be explained by an increase of GH which resulted from the depolarization alone. 4. Potassium-rich solutions influenced the conductance by increasing GH as the result of depolarization and by decreasing (blocking) GO. Small increases in the external potassium concentration (from 2.5 to 5 mM), which did not depolarize the lens, resulted in a decrease in resting conductance due to the blockade of GO. 5. Conductance-voltage relationships established in 2.5 (control), 5, 12.5 and 25 mM external potassium could each be fitted to a single mathematical model by assuming that GO had been reduced for 5.0 (control) to 4.5, 3 and 1 x 10(-5) S respectively by those increased potassium concentrations. 6. Barium (2 mM) depolarized the lens by 14.3 mV and decreased the resting conductance by 39%. When the lens was depolarized by a step current pulse in the presence of barium, the conductance increased with time after the onset of the current. Hyperpolarization elicited less time dependence of the conductance. 7. Barium reduced the extent to which lens conductance was dependent on voltage.