The influence of pH on membrane conductance and intercellular resistance in the rat lens

1. The conductance of the rat lens was measured using a two-internal-microelectrode technique. The voltage response to a step of current consisted of two components arising from bulk and membrane resistance respectively. 2. The potassium permeability was calculated by applying Goldman theory to 86Rb+ efflux data. 3. The internal pH (pHi) and internal free calcium (pCai) were measured directly using single- and double-barrelled ion-sensitive microelectrodes. 4. Lens pHi was 6.9 in control solution (external pH, pHo = 7.3) and was reduced on lowering pHo. The presence of propionate or 100% CO2 in the external solution accentuated this effect. 5. Internal acidification was accompanied by a depolarization of membrane potential, an increase in membrane and cell-to-cell resistance and a decrease in potassium permeability. The acidification had no effect on pCai. 6. The intracellular pH was increased by perifusing with trimethylamine or NH4Cl. Both treatments induced a membrane depolarization with little change in potassium permeability. Subsequent removal of NH4Cl led to a sustained decrease in pHi. 7. In every case where pHi decreased, the changes in membrane potential and conductance could be explained largely on the basis of a decrease in potassium permeability. The concomitant increase in cell-to-cell resistance was less pronounced and probably insufficient to uncouple the lens system.