Pathways of dephosphorylation of 1D-myo-inositol 1,4,5-trisphosphate in GH3 pituitary tumour cells

Resumen

Previous work in [ 3H]inositol-labelled GH3 pituitary tumor cells stimulated with thyrotropin-releasing hormone (TRH) reported the existence of at least ten distinct [ 3H]inositol-containing substances which were identified as different inositol moni-, bis- and tris-phosphate isomers [1]. Here a complete kinetic study of the dephosphorylation pathways of the second messenger Ins(1,4,5)P 3 is reported in GH3 cell homogenates, identifying a new intermediate, Ins(4,5)P 2, in the metabolism of the second messenger. In vitro results obtained with exogenous substrates are compared with in vivo results obtained measuring levels of the endogenous [ 3H]-inositol-labelled isomers that participate in the dephosphorylation pathways of Ins(1,4,5)P 3 in resting and TRH-stimulated GH3 cells. The effect of Li + on the activity of the different phosphatases involved in these pathways is studied as well.