Tosco Marisa, Faelli Alide, Gastaldi Giulia, Paulmichl Markus, Orsenigo Maria Novella
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università di Milano, Milano, Italy.
J Comp Physiol B. 2008 May;178(4):457-63. doi: 10.1007/s00360-007-0238-4. Epub 2008 Jan 8.
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.
非洲爪蟾卵母细胞中的碳通量是糖原生成性的，一种内源性单羧酸转运体负责细胞内乳酸的摄取。本研究的目的是确定蛋白激酶C和A的直接激活是否会调节乳酸转运体的活性，以及研究细胞骨架在这些调节现象中可能发挥的作用。通过在有无细胞骨架干扰毒素的情况下测量（14）C-乳酸摄取，在分离的V-VI期非洲爪蟾卵母细胞中研究了这种调节作用。我们发现基础乳酸转运体活性依赖于细胞骨架的完整性，因为细胞骨架紊乱会部分抑制该活性。蛋白激酶A和蛋白激酶C的激活均导致转运活性显著降低，且这种降低可被特异性蛋白激酶抑制剂阻断。所证实的效应并非相加性的。肌动蛋白丝或微管去稳定化试剂可消除转运抑制作用。我们得出结论，蛋白激酶A和C的作用均由细胞骨架介导，它们对非洲爪蟾卵母细胞的内源性乳酸转运体起负调节作用，这表明这些激酶可能在控制卵母细胞胞质丙酮酸/乳酸池方面发挥作用。
