Abstract
Permeation of several redox species through a cell membrane of a single algal protoplast (radius 100 μm) was investigated by amperometry with a Pt microdisk electrode (disk radius, 6.5 μm) located near the membrane. The redox current observed at the microelectrode decreased as the microelectrode approached the cell membrane since the membrane acted as a barrier for diffusion of redox species from bulk to the microelectrode. Permeability coefficient ( P m) of the protoplast membrane was determined by the quantitative analysis of the variation of the redox current with microelectrode-membrane distance using digital simulation. The P m values for Fe(CN) 6 4−, Fe(CN) 6 3−, Co(phen) 3 2+, ferrocenyl methanol(FMA) and p-hydroquinone(QH 2) were ⪕ 1.0 × 10 −4, ⪕ 1.0 × 10 -4, 1.0 × 10 −3, 5.0 × 10 −3 and 2.0 × 10 −2 cm/s , respectively. Using these P m values, the concentration changes inside a model cell and chloroplast we theoretically calculated.
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