Effects of cadmium ions, D-600 and chlorpromazine on the skinned smooth muscle of guinea-pig taenia coli

Abstract

1. 1. The effects of Cd 2+ on the skinned taenia coli were compared with that of Ca 2+ channel blocker, D-600 and calmodulin inhibitor, chlorpromazine. The Cd 2+ (0.001–0.5 mM) inhibited the contraction of skinned fibres in a dose-dependent manner. 2. 2. In contrast, the contraction of skinned fibres was not inhibited by pretreatment with 1 × 10 −6 M D-600. However, chlorpromazine (10 −4 M) inhibited the contraction of skinned taenia coli. 3. 3. The inhibition of contraction by Cd 2+ in skinned taenia coli was completely reversed by washing with solution containing EDTA, following a treatment with 0.5 mM Cd 2+ for 15 min. 4. 4. The skinned fibres had rapidly taken up a far greater amount of Cd 2+ than intact muscle of taenia coli. EDTA increased Cd 2+ efflux in skinned fibres and only 5% of the original tissue content retained. 5. 5. Thus, EDTA, which was ineffective on intact taenia coli, can be considered to act on Cd 2+ of intracellular compartment after disruption of the cell membrane with saponin. 6. 6. In conclusion, there is the possibility that Cd 2+ inhibits the contractile system, such as contractile proteins and calmodulin, which results in tension inhibitory effect.