Light-induced changes in membrane current in cone outer segments of tiger salamander and turtle

Abstract

The peak change in membrame conductance of vertebrate photoreceptors in response to the isomerization of a single photopigment was about 8 pS [siemens] in rods and 6 pS in cones. For rods, the estimate was largely confirmed by Yau, et al., by directly recording membrane current responses of rod outer segments to single photoisomerizations. No similar measurements were reported for cone outer segments. Direct recordings of membrane currents of single cone outer segments using an extracellular patch electrode were formed. The technique was similar to that described by Yau, et al. for toad rods. Dark currents of up to 40 pA were measured. The conductance change resulting from a single photoisomerization was calculated at less than 1 pS.