Effect of sulmazole and pimobendan on contractility of skinned fibres from frog skeletal muscle.

The influence of two benzimidazole derivatives, 2-[(2-methoxy-4-methylsulfinyl)phenyl]-1H-imidazo [4,5-b] pyridine (sulmazole, AR-L 115 BS) and 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]-5-methyl- 3(2H)- pyridazinone (pimobendan, UD-CG 115 BS) on the Ca2+-dependent isometric tension of skinned frog skeletal muscle fibres (tibialis anterior of Rana esculenta) was investigated. Both drugs sensitized the myofibrils of skeletal muscle for Ca2+: at a drug concentration of 2 X 10(-4) mol/l, sulmazole and pimobendan increased the isometric tension obtained at a Ca2+ concentration of 10(-6) mol/l by 21.7% and 49%, respectively.