Antagonism of calcium by zinc in guinea‐pig isolated taenia caeci and trachealis muscle

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Abstract
1 In guinea-pig isolated taenia caeci and trachealis bathed in a K+-rich, Ca2+-free medium, CaCl2 (0.01–10 mm) produced a concentration-dependent contraction. Zn2+ (0.01–1 mm), Cd2+ (0.01–1 mm), verapamil (0.01–100 μm) and trifluoperazine (1–100 μm) were effective antagonists of CaCl2-induced responses. 2 Zn2+ and Cd2+ in concentrations from 0.01 to 1 mm were without effect on the tone of taenia and trachea in normal Tris solution. Conversely, Zn2+ and Cd2+, in concentrations of 1 mm, caused contraction of these tissues in a K+-rich, Ca2+-free medium. Zn2+ (1 mm)-induced contractions of taenia and trachea were completely inhibited by verapamil (10 μm). 3 In taenia and trachea skinned of their plasma membranes, tension development induced by Ca2+ (10 μm or 1 μm, respectively) was unaffected by verapamil (100 μm), whereas trifluoperazine (100 μm) depressed the maximal tension produced by Ca2+. Segments of skinned preparations contracted in response to low concentrations of Zn2+ (10 μm) or Cd2+ (10 μm). 4 It is concluded that Zn2+ may suppress Ca2+-induced spasm by a direct action on the binding sites of the Ca2+ channel.