Impedance of the amphibian lens.

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Abstract
The electrical resistance of the perfused frog lens was measured using separate internal current passing and voltage measuring electrodes. The resistance values obtained using voltage clamp and direct and alternating current techniques were in good agreement. The voltage transients induced in response to current steps were multiexponential in form. Increasing the external K concentration reduced both the amplitude of the voltage response and the rise time. The impedance characteristics were investigated in more detail using alternating current analysis techniques. In an equivalent-circuit modeling study it was assumed that there were 2 major pathways for current flow in the lens: the 1st through the surface membranes, and the 2nd through the inner fiber membranes via the narrow extracellular spaces. The experimental impedance loci could not be adequately fitted by a simple 2 time constant model and a 3rd time constant was introduced which may represent diffusion polarization effects in the extracellular spaces. The 3 time constant model gave good and consistent fits to impedance data from a number of preparations. The form of the impedance loci was also dependent on the external K concentration, but the only fitted parameter which changed consistently with external K was the surface membrane resistance (RS).