Repetitive Ca2+ spikes in a unicellular green alga

Cytosolic Ca2+ activity ([Ca2+](cy)) and membrane potential were measured simultaneously in the unicellular green alga Eremosphaera viridis. Steady state [Ca2+](cy) was about 160 nM. A 'light-off' stimulus induced a transient elevation of [Ca2+](cy) ([Ca2+](cy) spike) in parallel with a transient hyperpolarization of the plasma membrane. Caffeine and Sr2+, known to release Ca2+ from intracellular stores in animal cells, induced repetitive [Ca2+](cy) spikes in Eremosphaera which were always accompanied by parallel repetitive transient hyperpolarizations. These transient hyperpolarizations could be used as an indicator for [Ca2+](cy) spikes. Repetitive [Ca2+](cy) spikes in Eremosphaera were similar to repetitive [Ca2+](cy) spikes in excitable animal cells. The mechanisms underlying these [Ca2+](cy) oscillations seem to be comparable in animal and plant cells. (C) 1997 Federation of European Biochemical Societies.