The Inhibitory Effect of Some Chlorinated Hydrocarbon Pesticides on the ATP‐Dependent Ca2+ Binding of the Particulate Fraction of the Eggshell Gland Mucosa Cells

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Abstract
The pesticide p‐p'‐DDT and its persistent metabolite p‐p'‐DDE cause thinning of the eggshells in several species of birds. In earlier investigations on ducks this thinning was found to be associated with a reduction of the ATP‐dependent Ca2+ binding to a homogenate of the shell gland mucosal cells by DDE. The activity of a Ca2+‐Mg2+‐activated ATPase in the homogenate was also decreased on administration of DDE in vivo. We have therefore investigated the in vitro effects of some other chlorinated hydrocarbon pesticides of ecotoxicological interest on the ATP‐dependent Ca2+ binding and the Ca2+‐Mg2+‐activated ATPase activity in a homogenate of the eggshell gland mucosa of the hen and determined the molar concentrations that produced 50% inhibition (= IC50). Several of the investigated compounds, namely toxaphene, chlordane, p‐p'‐DDD, o‐p'‐DDE, p‐p'‐DDT, methoxychlor and PCB (Arochlor 1242), had a similar IC50 to inhibit the Ca2+ binding as p‐p'‐DDE. Lindane, p‐p'‐DDA and biphenyl had an IC50 3.3–4 times higher and that of 2.4 D was 13.5 times higher than that of p‐p'‐DDE. When the IC50 of some of the compounds (p‐p'‐DDE, PCB, toxaphene, Lindane) was determined that decreased the Ca2+‐Mg2+‐activated ATPase of the homogenate it was found to be only 18 to 29 per cent of that needed to inhibit the Ca2+ binding by the homogenate. It is therefore probable that some other effect than inhibition of this enzyme is also involved in the Ca2+‐binding process and affected by the compounds.