Indicate true (T) and false (F) statements below regarding cellular signaling mediated by nitric oxide (NO). Your answer would be a four-letter string composed of letters T and F only, e.g. TTTF.
( ) Once produced, NO can diffuse to neighboring cells.
( ) NO has known roles in cGMP-independent as well as cGMP-dependent signaling.
( ) NO normally decreases cGMP concentration by activating cGMP phosphodiesterase.
( ) The drug Viagra® counteracts the effects of NO on penile blood vessels.