VACUOLAR ION CURRENTS IN THE PRIMITIVE GREEN-ALGA EREMOSPHAERA-VIRIDIS - THE ELECTRICAL-PROPERTIES ARE SUGGESTIVE OF BOTH THE CHARACEAE ANDHIGHER-PLANTS
Kw. Linz et K. Kohler, VACUOLAR ION CURRENTS IN THE PRIMITIVE GREEN-ALGA EREMOSPHAERA-VIRIDIS - THE ELECTRICAL-PROPERTIES ARE SUGGESTIVE OF BOTH THE CHARACEAE ANDHIGHER-PLANTS, Protoplasma, 179(1-2), 1994, pp. 34-45
The electrical properties of the vacuolar membrane of the primitive gr
een alga Eremosphaera virdis were investigated using the patch-clamp t
echnique. In whole vacuole measurements two types of transport systems
with long activation time-constants were identified. The first, showi
ng marked outward rectification, was activated by an increase in the c
ytosolic calcium concentration. Furthermore, it displayed sensitivity
to micromolar concentrations of the anion channel blocker Zn2+ and to
acidification of the cytosol. In contrast, the second time-activated c
urrent component was almost insensitive to changes in cytosolic pH and
was blocked by the potassium channel inhibitor TEA. In addition to th
ese slowly activating current components, the vacuolar membrane contai
ned at least two further transport systems, responsible for an instant
aneous current. These two current components were distinguished by the
ir different sensitivity to protons, cytosolic calcium, and TEA. Compa
ring these electrical properties to those observed in vacuoles of high
er plants or in cytoplasmic droplets from characean algae, respectivel
y, it seems that Eremosphaera is intermediate, corresponding to the sy
stematic position of this simple green alga.