Na+, K+-activated-ATPase inhibition in rainbow trout: A site for organochlorine pesticide toxicity?

1. The Na⁺, K⁺-activated, Mg²⁺-dependent-ATPase enzyme system in a heavy microsomal fraction of rainbow trout (Salmo gairdneri) brain was inhibited in vitro by chlorinated hydrocarbon pesticides.

2. T₅₀ (concentration at 50 per cent inhibition) values for dicofol, endosulfan and DDT were 5 × 10⁻⁶, 3 × 10⁻⁵ and 1 × 10⁻⁴ M respectively. Similar inhibition by these pesticides occurred in kidney and gill ATPase preparations.

3. An unexpected finding was a failure of the classic inhibitor, ouabain, to block the Na⁺, K⁺-activated component of ATPase activity in the gill.

4. It is suggested that inhibition of ATPase activity may be a causal factor in the toxic effects of organochlorine pesticides in fishes.