The effect of Ca2+ antagonists on spontaneous motility from sheep duodenum

Abstract

Abstract Longitudinal smooth muscle of the sheep duodenum showed a rhythmic spontaneous activity with an average frequency of 5·6 ± 0·55 phasic movements min−1 and a mean value of the amplitude of phasic contractions of 0·956 ± 0·1 g. When the strips were incubated in Ca2+-free medium, the spontaneous motility amplitude (SMA) was reduced to 37 ± 8·2% of control values. In Ca2+-free medium plus EDTA (1 or 2 Mm), the SMA was strongly reduced to 21·9 ± 8·3 and 1·8 ± 1·8%, respectively. Verapamil, nifedipine and diltiazem diminished the SMA. The EC50 value for verapamil was 10−9 M., whereas that for diltiazem was 2 × 10−9 M and for nifedipine was 3 × 10−14 M. Trifluoperazine and TMB-8 reduced the SMA with EC50 values of 7 × 10−6and 3 × 10−5  m, respectively. The spontaneous activity in the sheep duodenum seemed to be mediated by influx extracellular Ca2+, which enters through potential-dependent channels and intracellular Ca2+ release.