Diosmin‐induced increase in sensitivity to Ca²⁺ of the smooth muscle contractile apparatus in the rat isolated femoral vein

The effect of diosmin, a flavone derivative, on the Ca2+ sensitivity of the venous contractile apparatus was investigated in chemically (beta-escin) skinned strips from the rat isolated femoral vein. Diosmin (0.5-10 microM) shifted to the left the concentration-response curve to Ca2+ (0.05-5 microM). The maximal effect was observed in the presence of 1 microM diosmin which increased the contractile response evoked by 0.15 microM Ca2+ from 26.3% to 78.9% of the maximal Ca(2+)-induced response. This work demonstrates that the venotonic action of diosmin involves an increase in the Ca2+ sensitivity of the contractile apparatus. Such a mechanism of action could represent a new and important means of therapeutic control of vasomotor activity.