Effect of heavy metals and lanthanum on sugar transport in isolated guinea pig left atria

Abstract

The effect of heavy metals on sugar transport in fully resting guinea pig left atria was studied by measuring the tissue–medium distribution of 3-methylglucose. Basal sugar transport was increased significantly by all heavy metals tested (Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺ (2 mM)) and by La³⁺ (0.05 mM) but 1 mM La³⁺ had no effect. The stimulation of sugar transport by insulin, hyperosmolarity, K⁺-free medium, or 10⁻⁵ M ouabain was strongly antagonized by Ni²⁺, Zn²⁺, and La³⁺ but was unaffected by Co²⁺ and Mn²⁺. The heavy metals did not affect intracellular Na²⁺ and K⁺, whether in the basal state or when the Na⁺ pump was depressed by ouabain or K⁺-free medium. The data suggest that Ca²⁺ antagonistic ions may affect sugar transport both by inhibiting Ca²⁺ influx and by competing with Ca²⁺ for specific binding sites presumably involved in the regulation of sugar transport.