Intracellular potassium activity and cell membrane potential of the isolated human and rabbit lens

Abstract

Intracellular potassium activities (aKi) determined with single-barrelled K-selective ion exchanger (Corning 477317) microelectrodes and cell membrane potentials (VM) were measured across the electrically separated anterior and posterior surfaces (Ussing-type chamber) of the human and rabbit lens. aKi amounted to 88·3±1·9 mmol/l and to 120·4±1·6 mmol/l in the human and rabbit lens, respectively. aKi was equally distributed on both anterior and posterior lens sides. The potassium activities measured indicate that in both human and rabbit lens potassium is essentially free. The calculated potassium equilibrium potential (EK) amounted to −82·5±0·6 mV and to −91·3±0·3 mV in the human and rabbit lens, respectively. Thirty minutes after exposure to 10−3 mol/1 ouabain, aKi was significantly reduced in both species. The anterior and posterior VM exhibited mean values of −23·8±0·6 mV and −18·3±0·6 mV, respectively, in the human lens. In the rabbit lens the anterior VM was −55·3±1·8 mV and on the posterior side −35·9±1·7 mV. In both species the anterior-posterior difference of VM compared well with the simultaneously measured translenticular potential difference. Because EK always greatly exceeded VM, potassium must be actively accumulated across the lens surfaces. The low VM, despite high intracellular potassium, is probably due to a considerable contribution of Na-permeability to the cell membrane potential.