Formula omitted] uptake in isolated bovine adrenal chromaffin cells

Abstract

The characteristics and regulatory nature of sugar transport in freshly isolated bovine adrenal chromaffin cells were investigated. Transport was measured by following the cell/medium distribution of the non-metabolizable glucose analogue, 3-O- methyl- d-glucose . The uptake of 3-O- methyl- d-glucose was mediated by a saturable transport system with a K m of 8.2 mM and a V max of 0.69 nmol/mg protein per min. Basal 3-O- methyl- d-glucose transport was competitively inhibited by d-glucose and a countertransport effect was demonstrated. Cytochalasin B and phloretin, which are specific inhibitors of carrier-mediated glucose transport, significantly decreased basal 3-O- methyl- d-glucose uptake. Basal transport was stimulated by 50 mU/ml insulin, an effect associated with an increase in V max. The stimulatory effect of insulin was depressed in medium lacking external Ca 2+, or containing the Ca 2+-antagonistic ion, La 3+, or the Ca 2+ channel blocker, methoxyverapamil (D-600). The data suggest that the uptake of 3-O- methyl- d-glucose in freshly isolated bovine adrenal chromaffin cells is mediated by a specific facilitated diffusion mechanism, and is subject to regulation by insulin, thus resembling sugar transport in muscle. In addition, the insulin effect appears to depend on the presence of extracellular Ca 2+.