Production of cGMP in RFL-6 reporter cells coincubated with transfected U937 cells. (A) RFL-6 cells were incubated with U937 cells transfected with the iNOS gene, the empty vector, or the eNOS gene, without or with L-NMA (500 μmol/L) as shown (see Materials and Methods). (B) RFL-6 cells were incubated with eNOS or empty vector transfected cells in the presence or absence of A2318 (1 μmol/L), a calcium ionophore, and without or with L-NMA (500 μmol/L). Data are means ± SE (n = 3 for both experiments).