Multiple AMPK activators inhibit L-Carnitine uptake in C2C12 skeletal muscle myotubes



Shaw A, Jeromson S, Watterson KR, Pediani JD, Gallagher IJ, Whalley T, Dreczkowski G, Brooks N, Galloway SD & Hamilton DL (2017) Multiple AMPK activators inhibit L-Carnitine uptake in C2C12 skeletal muscle myotubes. American Journal of Physiology - Cell Physiology, 312 (6), pp. C689-C696.

Mutations in the gene that encodes the principal L-Carnitine transporter, OCTN2, can lead to a reduced intracellular L-Carnitine pool and the disease Primary Carnitine Deficiency. L-Carnitine supplementation is used therapeutically to increase intracellular L-Carnitine. As AMPK and insulin regulate fat metabolism and substrate uptake we hypothesised that AMPK activating compounds and insulin would increase L-Carnitine uptake in C2C12myotubes. The cells express all three OCTN transporters at the mRNA level and immunohistochemistry confirmed expression at the protein level. Contrary to our hypothesis, despite significant activation of PKB and 2DG uptake, insulin did not increase L-Carnitine uptake at 100nM. However, L-Carnitine uptake was modestly increased at a dose of 150nM insulin. A range of AMPK activators that increase intracellular calcium content [caffeine (10mM, 5mM, 1mM, 0.5mM), A23187 (10μM)], inhibit mitochondrial function [Sodium Azide (75μM), Rotenone (1μM), Berberine (100μM), DNP (500μM)] or directly activate AMPK [AICAR (250μM)] were assessed for their ability to regulate L-Carnitine uptake. All compounds tested significantly inhibited L-Carnitine uptake. Inhibition by caffeine was not dantrolene (10μM) sensitive. Saturation curve analysis suggested that caffeine did not competitively inhibit L-Carnitine transport. However, the AMPK inhibitor Compound C (10μM) partially rescued the effect of caffeine suggesting that AMPK may play a role in the inhibitory effects of caffeine. However, caffeine likely inhibits L-Carnitine uptake by alternative mechanisms independently of calcium release. PKA activation or direct interference with transporter function may play a role.

American Journal of Physiology - Cell Physiology: Volume 312, Issue 6

Publication date30/06/2017
Publication date online15/03/2017
Date accepted by journal14/03/2017
PublisherAmerican Physiological Society

People (4)


Dr Naomi Brooks
Dr Naomi Brooks

Senior Lecturer, Sport

Dr Iain Gallagher
Dr Iain Gallagher

Lecturer in Health & Exercise, Sport

Professor Stuart Galloway
Professor Stuart Galloway

Professor, Sport

Professor Tim Whalley
Professor Tim Whalley

Professorial Fellow, Biological and Environmental Sciences