cGMP induces potassium influx in Blastocladiella zoospores. Δ[K+]i, variation in potassium influx; F/F0, peak fluorescence intensity divided by basal fluorescence intensity. KCl (60 mM), cGMP (3 mM), or cAMP (3 mM) was added to the zoospore suspension, and fluorescence emission rates were recorded. Data are mean values ± SE for three independent experiments performed in triplicate. *, P < 0.05.