Effects of flavone on the contractile activity of the circular smooth muscle of the rabbit middle colon in vitro

The circular smooth muscles of the middle colon of the rabbit generate giant contractions of high amplitude and low frequency. Flavone, at various concentrations, reduces the giant contractions and the tonic contraction induced by 10 µM carbachol and 80 mM KCl. The contractions induced by dequalinium and tetraethylammonium are reduced by flavone (30 µM). At 100 µM, flavone decreases the contraction induced by 100 µM methylene blue and 1 mM orthovanadate. These results suggest that flavone inhibit the giant contractions by (1) inhibition of voltage-dependent Ca2+ channels, (2) activation of guanyl cyclase, (3) opening of K+ channels and (4) inhibition of tyrosines kinases.