Abstract
The distribution of ( 14C)-3-0-methyl-D-glucose and of ( 45Ca) was followed in perifused left atria and intact hemidiaphragms of the rat. The carboxylic calcium ionophore A-23187 affected sugar and Ca 2+ influx in parallel, with low concentrations inhibiting and higher ones stimulating influx under basal conditions. The stimulation of sugar transport by insulin, high concentrations of adrenaline or ouabain, or by K +-free medium was antagonized by the calcium ionophore. Likewise, A-23187 counteracted the depression of sugar transport caused by low concentrations of ouabain or adrenaline. These results support a role of Ca 2+ in the regulation of sugar transport in muscle. However, increased influx of Ca 2+ cannot explain all the effects of A-23187. It is suggested that the ionophore may also act by releasing Ca 2+ from intracellular storage and binding sites.
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