Nonmetabolizable glucose analogues and ornithine decarboxylase expression in LLC-PK1 cells

Abstract

This report examines the effect of nonmetabolizable glucose analogues on ornithine decarboxylase (ODC) activity in LLC-PK1 cells. The addition of Na(+)-dependent cotransported glucose analogues, 1-O-methyl-alpha-D-glucopyranoside (alpha-MDG) and 1-O-methyl-beta-D-glucopyranoside, to Earle's balanced salt solution minus glucose (EBSS-G) increased ODC activity five- to sevenfold above basal levels. The passive carrier-mediated transported glucose analogue 3-O-methyl-D-glucopyranose had very little effect on enzyme activity. alpha-MDG increased ODC activity in quiescent but not growing cells. ODC activity increased as a function of both the incubation time in EBSS-G + alpha-MDG and the concentration of alpha-MDG in EBSS-G. Phlorizin significantly reduced the level of enzyme activity induced by alpha-MDG. ODC expression by alpha-MDG was reduced in cells incubated in hypertonic EBSS-G + alpha-MDG. Enzyme activity, in the absence of extracellular organic substrates, was markedly elevated in cells incubated in hypotonic media. It is suggested that an influx of Na+ and/or an increase in cell volume elevates one or more signal transducers that regulate ODC expression.