Figure 8.

Ammonium Increases Intracellular Levels of NO and cGMP.

Fluorescence due to intracellular NO levels after incubation with the indicated nitrogen sources was determined using DAF-FM DA and is expressed as arbitrary units.

(A) Cells were grown in 8 mM ammonium medium, washed, and transferred to N-free medium and media containing 100 μM nitrate plus the indicated concentration of ammonium for 1 h, and then fluorescence was determined.

(B) cGMP concentration was determined from cells grown in 8 mM ammonium (A) medium, washed, and transferred for 1 h to the indicated medium. Amounts of cGMP are expressed as fmol/10⁶ cells. The error bars represent the sd of three biological replicates.