Effects of propafenone on 45Ca movements and contractile responses in vascular smooth muscle

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Abstract
In rat isolated aorta the class Ic antiarrhythmic drug, propafenone, dose‐dependently inhibited the contractile responses induced by high K (80 mm) and noradrenaline (NA, 10−5 m), the IC50s being 2.5 ± 0.7 × 10−6 m and 8.7 ± 0.8 × 10−6 m, respectively. These inhibitory actions were also observed with propafenone added after the induced contractions. Contractile responses induced by addition of Ca to 0 Ca high‐K solution were also inhibited by propafenone (IC50 = 2.5 ± 0.8 × 10−6 m). Moreover, propafenone inhibited the contractile responses elicited by NA in strips incubated in 0 Ca (IC50 = 1.9 ± 0.9 × 10−6 m). Propafenone also inhibited (IC50 = 1.2 ± 0.4 × 10−5 m) the development of spontaneous mechanical activity in portal vein segments. Propafenone, 5 × 10−6 m and 10−5 m, inhibited 45Ca uptake stimulated by high K or NA without altering 45Ca uptake in resting strips. These results indicated that in rat isolated aortae and portal veins propafenone inhibited Ca entry through voltage‐operated channels and NA‐induced Ca uptake as well as Ca release from intracellular stores. As a consequence it would reduce the concentration of intracellular free Ca available at the contractile apparatus for vascular smooth muscle contraction.