REPETITIVE CA2-ALGA( SPIKES IN A UNICELLULAR GREEN)

Cytosolic Ca2+ activity ([Ca2+](cy)) and membrane potential were measu red simultaneously in the unicellular green alga Eremosphaera viridis. Steady state [Ca2+](cy) was about 160 nM. A 'light-off' stimulus indu ced a transient elevation of [Ca2+](cy) ([Ca2+](cy) spike) in parallel with a transient hyperpolarization of the plasma membrane. Caffeine a nd Sr2+, known to release Ca2+ from intracellular stores in animal cel ls, induced repetitive [Ca2+](cy) spikes in Eremosphaera which were al ways 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 si milar to repetitive [Ca2+](cy) spikes in excitable animal cells. The m echanisms underlying these [Ca2+](cy) oscillations seem to be comparab le in animal and plant cells. (C) 1997 Federation of European Biochemi cal Societies.