Coupled Glucose Transport and Metabolism in Cultured Neuronal Cells: Determination of the Rate-Limiting Step

Author:

Whitesell Richard R.1,Ward Michael2,McCall Anthony L.2,Granner Daryl K.1,May James M.13

Affiliation:

1. Departments of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, Portland, Oregon, U.S.A.

2. Departments of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, Portland, Oregon, U.S.A.

3. Departments of Cell Biology and Anatomy, Oregon Health Sciences University, and Diabetes Program, Department of Veterans Affairs, Portland, Oregon, U.S.A.

Abstract

In brain and nerves the phosphorylation of glucose, rather than its transport, is generally considered the major rate-limiting step in metabolism. Since little is known regarding the kinetic coupling between these processes in neuronal tissues, we investigated the transport and phosphorylation of [2-3H]glucose in two neuronal cell models: a stable neuroblastoma cell line (NCB20), and a primary culture of isolated rat dorsal root ganglia cells. When transport and phosphorylation were measured in series, phosphorylation was the limiting step, because intracellular glucose concentrations were the same as those outside of cells, and because the apparent Kmfor glucose utilization was lower than expected for the transport step. However, the apparent Kmwas still severalfold higher than the Kmof hexokinase I. When [2-3H]glucose efflux and phosphorylation were measured from the same intracellular glucose pool in a parallel assay, rates of glucose efflux were three- to-fivefold greater than rates of phosphorylation. With the parallel assay, we observed that activation of glucose utilization by the sodium channel blocker veratridine caused a selective increase in glucose phosphorylation and was without effect on glucose transport. In contrast to results with glucose, both cell types accumulated 2-deoxy-d-[14C]glucose to concentrations severalfold greater than extracellular concentrations. We conclude from these studies that glucose utilization in neuronal cells is phosphorylation-limited, and that the coupling between transport and phosphorylation depends on the type of hexose used.

Publisher

SAGE Publications

Subject

Cardiology and Cardiovascular Medicine,Neurology (clinical),Neurology

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