IngentaConnect Long-lasting contractile action and the inhibitory action of cupr...

Abstract:

Summary

1 Cupric ions (Cu²⁺), at concentrations above 0.03 mm, induced a progressive increase in the tonic contraction of guinea-pig ileal longitudinal muscle. Maximal contraction of 0.1 mmCu²⁺ attained a level above that of the 60-mmK⁺-induced tonic response, within 20 min of application. The tension induced by Cu²⁺ persisted for more than several hours. Tetrodotoxin (3 × 10⁻⁶ m) had no effect on the contraction induced by 0.1 mmCu²⁺.

2 After incubation in a Ca²⁺-free medium, the ileal response to 0.1 mmCu²⁺ was lost. Nifedipine, a L-type Ca²⁺ channel blocker, dose-dependently inhibited contractions induced by Cu²⁺.

3 As the duration of the first application of 0.1 mmCu²⁺ increased above 30 min, after washing with normal medium, the contractile response to a second application of 0.1 mmCu²⁺ decreased gradually. After 150 min of the first application of 0.1 mmCu²⁺, a second application of Cu²⁺ could not evoke any contraction.

4 After the application of 0.1 mmCu²⁺ for 150 min, when muscles were washed with a medium containing 1 mmEDTA, the response to 0.1 mmCu²⁺ returned to a greater extent in the normal Ca²⁺ medium.

5 In conclusion, Cu²⁺ (0.1 mm) induced a maximal ileal tension above that of the K-induced tonic response within 20 min. The ileal contraction to Cu²⁺ persisted for more than several hours and depended on extracellular Ca²⁺ concentrations. It is possible that a part of Cu²⁺, bound to a EDTA-inaccessible site, also has a tension inhibitory effect.

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Long-lasting contractile action and the inhibitory action of cupric ions on ileal longitudinal muscle