The Effect of Zinc and Certain Other Bivalent Metal Ions on the Isometric Tension Development of Glycerol‐extracted Muscle Fibre Bundles.

The effect of several bivalent metal ions on the ATP-induced contraction of glycerol-extracted rabbit psoas fibre bundles has been studied under highly isometric conditions. The relaxing effect of these metals on previously contracted fibre bundles in the presence of 1 mM magnesium and in the presence or absence of ATP has also been investigated. Zinc, (≥ 0.01 mM), cadmium (≥ 0.1 mM), calcium (≥ 10 mM) and mercury (≥ 0.01 mM) partly or wholly inhibit, the contraction. In lower concentrations, however, zinc (0.001 mM) and calcium (0.32 mM) produce an increase, in the final tension but have no significant effect, (calcium) or an inhibiting action (zinc) on the initial phase of the contraction. In the presence of 0.4 mM ATP, 0.025–0.88 mM zink induces relaxation of a previously contracted fibre bundle. The contraction-relaxation cycle can be repeated many times. In the absence of ATP. no relaxing effect could he demonstrated for zinc (≥ 0.88 M). A less reversible relaxation, as compared with that of zine, is obtained with cadmium(5 mM and 1 mM) ill the presence of 0.4 mM ATP. Mercury (0.1 mM) produces a slow relaxation together with 0.4 mM ATP the relaxation is irreversible after 15 minutes' incubation with mercury, however. Calcium, cobalt and manganese (10 mM) bring about a slight decrease in tension of a contracted fibre bundle in the presence of 0.4 mM ATP. A certain decrease in tension can he demonstrated for calcium (10 mM). strontium (10 mM) and mercury (0.1 mM) in the absence of ATP. In the discussion it is stressed that, the complexing of metal ions by ATP greatly complicates the interpretation of findings obtained in studies of the interactions of metals, ATP and contraetile proteins.