Stimulus-secretion coupling of arginine-induced insulin release: metabolism of l-arginine and l-ornithine in tumoral islet cells

Abstract

The metabolism of l-arginine and l-ornithine was examined in tumoral islet cells of the RINm5F line and compared to the situation previously characterized in normal rat islets. The maximal velocity of arginase in cell homogenates, as well as either the production of 14C-urea or the steady-state content of 14C-labelled ornithine in intact cells exposed to l-[U- 14C]arginine were about one order of magnitude lower in tumoral than normal islet cells. The activity of ornithine-glutamate transaminase was similar in both cell types, and this coincided with a comparable rate of 14C-labelled l-glutamate generation by intact cells exposed to l-[1- 14C]ornithine. Despite a comparable cell content in 14C-labelled ornithine of normal and tumoral cells exposed to exogenous ornithine, the rate of di- and polyamine generation was about one order of magnitude higher in tumoral than normal islet cells, this coinciding with a much higher activity of ornithine decarboxylase in RINm5F cell than islet homogenates.