NOS levels during differentiation of erythroid cells. (A) eNOS mRNA levels during differentiation of erythroid cells. (B) iNOS mRNA levels during differentiation of erythroid cells; (C,D) eNOS protein levels during differentiation of erythroid cells: as measured by ELISA (C) and Western blotting compared with actin protein levels as a control (D). Vertical lines have been inserted to indicate a repositioned gel lane (n = 3). Values are means (± SEM). **P < .01 compared with cells at day 0.