Steady state voltages in the frog lens

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Abstract
Electro-chemical steady state in the lens depends on the transport properties of its various constituent cells. These transport properties, at a minimum, include the active transport of Na/K and the passive leak of Na, K and CI through membrane channels. The work of Kinsey and Reddy (1), first localized active Na/K transport to the anterior surface cell membranes. In this paper, we estimate that the pump current density is 2 to 4 v amp/cm2 of surface membrane, by measuring the change in intracellular voltage when the lens is exposed to 100 uM ouabain. Our impedance data suggest the passive leak of K is mostly across the membranes of surface cells, but whether these are anterior or posterior cells is not yet known. Membranes of the fiber cells throughout the volume of the lens appear to have channels that are selective for Na and CI but few K channels. A simple model of electro-chemical steady state is derived to relate localized transport properties to the resting voltages in the lens. The above described localization of properties predicts radially circulating currents at steady state and spatial gradients in the intracellular and extracellular voltages. These predictions are compared to our measurements of steady state voltages and we find good agreement.