Ca 2+ Homeostasis alterations induced by 2,4-dichlorophenoxyacetic butyl ester and 2,4-dichlorophenoxyacetic acid on avian skeletal muscle

Abstract

Fertilized hen eggs were treated externally with 2,4-dichlorophenoxyacetic butyl ester (2.4-D b.e.) (3.1 mg/egg) before the start of the incubation. Actomyosin and sarcoplasmic reticulum adenosine triphosphatase (ATPase) activities from leg and complexus muscles of chicks hatched from treated eggs were measured. No significant variations were detected in the ATPase activities of actomyosin, but the sarcoplasmic reticulum Mg 2+-activated ATPase and Ca 2+, Mg 2+-activated ATPase were inhibited 50 and 38% respectively. 45Ca 2+ uptake into soleus muscle was increased by the 2,4-D b.e. treatment. The compartmental analysis of 45Ca 2+ uptake kinetics showed increases in Ca 2+ fluxes in sarcolemma and mitochondria and in the mitochondrial calcium pool. Isolated soleus muscles were treated with 2,4-dichlorophenoxyacetic acid (2.4-D) or 2,4-D b.e. [ 14C]2,4-D reached it highest level in these muscles after 1 hr of treatment. The in vitro treatment with 2,4-D or 2,4-D b.e. increased 45Ca 2+ uptake into the muscles. 2,4-D b.e. produced greater alterations than 2,4-D. The compartmental analysis of the 45Ca 2+ uptake kinetics also showed increases of the mitochondrial Ca 2+ pool and Ca 2+ fluxes through sarcolemma and mitochondria. These results led to a hypothesis based on Ca 2+ permeability alterations for explaining the myopathic actions of these phenoxyherbicides.