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This Article Full Text Full Text (PDF) All Versions of this Article: 295/6/C1602    most recent 00090.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Carranza, A. Articles by Nowicki, S. Search for Related Content PubMed PubMed Citation Articles by Carranza, A. Articles by Nowicki, S.

RECEPTORS AND SIGNAL TRANSDUCTION

Signaling cascade of insulin-induced stimulation of L-dopa uptake in renal proximal tubule cells

¹Centro de Investigaciones Endocrinológicas-Consejo Nacional de Investigaciones Científicas y Técnicas (CEDIE-CONICET), Buenos Aires; and ²Facultad de Ciencias Biomédicas, Universidad Austral, Buenos Aires, Argentina

Submitted 15 February 2008 ; accepted in final form 2 October 2008

The inward L-dihydroxyphenylalanine (L-dopa) transport supplies renal proximal tubule cells (PTCs) with the precursor for dopamine synthesis. We have previously described insulin-induced stimulation of L-dopa uptake into PTCs. In the present paper we examined insulin-related signaling pathways involved in the increase of L-dopa transport into isolated rat PTCs. Insulin (50–500 µU/ml) increased L-dopa uptake by PTCs, reaching the maximal increment (60% over the control) at 200 µU/ml. At this concentration, insulin also increased insulin receptor tyrosine phosphorylation. Both effects were abrogated by the tyrosine kinase inhibitor genistein (5 µM). In line, inhibition of the protein tyrosine phosphatase by pervanadate (0.2–100 µM) caused a concentration-dependent increase in both the uptake of L-dopa (up to 400%) and protein tyrosine phosphorylation. A synergistic effect between pervanadate and insulin on L-dopa uptake was observed only when threshold (0.2 µM), but not maximal (5 µM), concentrations of pervanadate were assayed. Insulin-induced stimulation of L-dopa uptake was also abolished by inhibition of phosphatidylinositol 3-kinase (PI3K; 100 nM wortmannin, and 25 µM LY-294002) and protein kinase C (PKC; 1 µM RO-318220). Insulin-induced activation of PKC- was confirmed in vitro by its translocation from the cytosol to the membrane fraction, and in vivo by immunohistochemistry studies. Insulin caused a wortmannin-sensitive increase in Akt/protein kinase B (Akt/PKB) phosphorylation and a dose-dependent translocation of Akt/PKB to the membrane fraction. Our findings suggest that insulin activates PKC-, and Akt/PKB downstream of PI3K, and that these pathways contribute to the insulin-induced increase of L-dopa uptake into PTCs.

amino acid transport; second messengers; dopamine