An electrophysiological study of the membrane in aplanospore-like cell of Boergesenia forbesii

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Membrane potential and resistance, each of which was the sum of those of the plasmalemma and tonoplast, measured in the coenocytic thallus of Boergesenia forbesii were 6.7 mv inside positive and 2.8 kΩ・cm^2 respectively. Protoplasm squeezed from the thallus into artificial sea water (ASW) formed numerous spherical bodies, which are termed aplanospore-like cells (simply "spores"). The following electrical properties of the "spores" 20- 40 hr after squeezing were obtained: potential difference (p.d.) across plasmalemma (E_<co>) was -66 mv (-means inside negative), plasmalemma resistance 665 Ω・cm^2, p.d. across the tonoplast (E_<vc>) +73 mv, and tonoplast resistance 2.6 kΩ・cm^2. Tenfold increase in external [K^+] caused +45 mv change in E_<co> and +1 7 mv in E_<vc>. The plasmalemma was entirely depolarized in Ca^<++>-free ASW or ASW containing Triton X-100. When the "spore" was immersed in potassium-rich (277 mM) ASW. E_<co> was almost zero and the tonoplast showed two states (I and II, E_<vc> about +70 mv and +20 mv, respectively) . Eve went back and forth between the two states spontaneously or when a small current was applied. In most cases oscillatory changes in E_<vc> occurred after the lapse of a long time in the K^+-rich sea water. Membrane resistances in states I and II were 5 and 9 kΩ・cm^2 respectively.