Membrane electrical behaviour in nitellopsis obtusa

Abstract

The electrical properties of the two membranes, plasmalemma and tonoplast, bounding the cytoplasm of 'the brackish water characean, NitellopBiB obtUBa, were studied. In a solution approximating the natural pond water, the electrical potential difference between cytoplasm and outside was -141 mY, and between vacuole and cytoplasm +19 mY. The resistance of the plasmalemma was 80,000 cm2, and of the tonoplast, 10,000 n cm2. During an action potential, the peak values of the p.d.'s across plasmalemma and tonoplast were -25 and +57 mY respectively. The action potential was accompanied by a transient decrease in the resistance of the plasmalemma to' 5700 Ω cm2, and of the tonoplast to 2500 n cm2. The effects of changes in external potassium and calcium concentrations on the p.d.'s and resistances of the membranes were examined. During an action potential there was an increased chloride efflux from the vacuole to the outside of the cell. It is concluded that as in other characean species, a transient increase in the permeability of both plasmalemma and tonoplast to chloride ions is responsible for the action potential. © 1970 CSIRO.