Effect of Some Metal Compounds on the Ca2+ Binding and Ca2+‐Mg2+‐ATPase Activity of Eggshell Gland Mucosa Homogenate from the Domestic Fowl

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Abstract
Some metal ions, e.g. Hg2+, Cd2+ and Al3+, can have the effects as ecotoxicological agents, of causing eggshell thinning and breakage in birds. In a homogenate of the Ca2+-secreting part of the eggshell gland mucosa, a study was made of the influence of Hg2+, Cd2+, Cu2+, Pb2+, methyl-Hg+, Zn2+, V3+, Al3+ and Ni2+ in different concentrations on the rate of ATP-dependent 10-4 M Ca2+ binding. All compounds had an inhibitory action. The most potent metal (Hg2+) produced 50% inhibition (IC50) at 1.1 .times. 10-6 M, whereas this value for the least potent compound (Ni2+) was 9 .times. 10-4 M. The specific Ca2+-Mg2+-ATPase activity was also inhibited by the tested metal ions. In all cases except methyl-Hg+ the IC50 for this activity was lower than that for Ca2+-binding. The most potent ion on this respect was Cd2+, with an IC50 of 8 .times. 10-8 M, and the least potent was methyl-Hg+, with an IC50 of 1.4 .times. 10-3 M. Pb2+ and Cd2+ in a concentration range of 10-5-10-4 stimulated the Mg2+-ATPase activity, however, to almost the same extent as 10-4 M Ca2+. A possible explanation for this effect is that these ions may have an affinity for sites of Ca2+ binding of the polypeptide calmodulin and thereby influence the Ca2+ metabolism of the shell gland mucosa.