Endogenous lactate transport in Xenopus laevis oocyte: dependence on cytoskeleton and regulation by protein kinases.
Carbon flux in Xenopus laevis oocyte is glycogenic and an endogenous monocarboxylate transporter is responsible for intracellular lactate uptake. The aim of the present study was to determine if direct activation of protein kinases C and A modulates the activity of lactate transporter, as well as to investigate the possible role of cytoskeleton in these regulatory phenomena. The modulation was studied in isolated Xenopus oocytes of stage V-VI by measuring (14)C-lactate uptake, both in the absence and in the presence of cytoskeletal-perturbing toxins. We found that the basal lactate transporter activity depends on the integrity of the cytoskeleton since it is partially inhibited by cytoskeleton disorganisation. Both PKA and PKC activation caused a significant decrease in transport activity and this decrease could be blocked by specific protein kinase inhibitors. The evidenced effects were not additive. Transport inhibition was annulled by agents that destabilize actin filaments or microtubules. We conclude that both protein kinases A and C, whose effects are mediated by cytoskeleton, negatively regulate the endogenous lactate transporter of Xenopus oocyte, suggesting that these kinases may have a role in the control of cytosolic pyruvate/lactate pool in the oocyte.
Tosco
Marisa
M
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università di Milano, Milano, Italy. marisa.tosco@unimi.it
Faelli
Alide
A
Gastaldi
Giulia
G
Paulmichl
Markus
M
Orsenigo
Maria Novella
MN
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology; D029867:Xenopus Proteins / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
D020536:Enzyme Activators; D027501:Monocarboxylic Acid Transporters; D047428:Protein Kinase Inhibitors; D050257:Tubulin Modulators; D029867:Xenopus Proteins; D019344:Lactic Acid; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C