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.

Effects of strontium on calcium-dependent hexose transport in muscle

“…1979; Elbrink and Bihler 1975). Also, drugs and ions described as antagonistic to Ca" inhibited both ca2+ influx and hexose transport in parallel (Bihler and Sawh 1980;Bihler et al 1980). …”

“…For example, it was found (Bihler et al 1980) that several heavy metal ions, in addition to opposing sugar transport stimuIatBtlon by various factors, also increased 3-MG uptake in the absence of Ca2", suggesting that they may interact with ea2+ -specific binding sites, acting as partial agonists. Alternatively, they could act by displacing ~a " from membrane stabilizing sites.…”

“…Stimulation of hexose transport in muscle by a wide variety of agents is associated with increased influx of ca2' across the sacolemma and (or) with the release of c a 2 + horn intracellular storage sites (Clausen 1980;Sorensen et al 1980;Bigornia and Bihler 1985). As well, the presence of external ~a " + is required for the full expression of stimulation by insulin in skeletal and cardiac muscle (Bihler 1972;Bikles and Sawh 19801, and hexose transport stimulation is inhibited by heavy metal ions and lanthanides and by a calcium channel antagonist dmg (Bihler et al 1980;Bihler and Sawh 1977;Bihler and Sawh 1980).…”