Abstract.Accumulation of the lipophilic cation tri‐phenylmethylphosphonium (TPMP+) has been used to estimate the plasmalemma potential (Φm) of Porphyra purpurea (Rhodophyta, Bangiales) and Ulva lactuca (Chlorophyta, Ulvales). Values of Φm obtained using the Nernst equation were −61 mV and −54 mV respectively; these values compare well with those obtained using glass microelectrodes. A trend of hyperpolarization of Φm in P. purpurea was observed with decreasing external salinity. This hyperpolarization was shown to be primarily due to changes in external K+concentration. Varying external Na+concentration was found to have little effect on Φm. The present data suggest that the membrane potential of P. purpurea is not wholly due to a K+diffusion potential, but may have an electrogenic component.
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Reed et al. (1981) studied this question.
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