Experiments with AR-L 115 BS on skinned cardiac fibers.

Cardiac muscle fragments with disrupted sarcolemmas were obtained by homogenizing the ventricles of guinea pig hearts. Force and frequency of the spontaneous contractions of these fragments were measured under control conditions and after adding 2-[(2-methoxy-4-methylsulfinyl)phenyl]-1H-imidazo[4,5-b]pyridine (AR-L 115 BS), caffeine or dihydro-ouabain. The effects of AR-L 115 BS and caffeine were very similar. Probably AR-L 115 BS, like caffeine, releases calcium from the sarcoplasmic reticulum and inhibits the reuptake of calcium.