Potassium Transport Across the Membranes ofChara

Abstract

Smith, J. R., Walker, N. A. and Smith, F. A. 1987. Potassium transport across the membranes of Chara. III. Effects of pH, inhibitors and illumination.—J. exp. Bot. 38: 778–787. The effects of several treatments, normally used to inhibit electrogenic proton transport, upon the potassium permeability (Pk) of the membranes of Chara were examined by means of simultaneous measurements of the 42K influx (ϕinK) and the membrane electrical conductance (Gm). ϕinK, PK and Gmwere found to be substantially unaffected when the external pH (pH°) was varied over the range 5·0 to 85. However, when pH° was increased to 11 it was found that, although Gm increased considerably, both Pk and ϕinK decreased typically by an order of magnitude. When cells were placed in total darkness, PK decreased substantially only after one day had elapsed. For the particular experimental conditions used, the inhibitors DES, NaN3, and La3+ were found to alter PK, whereas DCCD left PK substantially unaffected. These results suggest that care must be taken with some common procedures used to examine the electrical properties of the electrogenic proton pump.