CaMKK is an upstream signal of AMP-activated protein kinase in regulation of substrate metabolism in contracting skeletal muscle

Abbott MJ, Edelman AM, Turcotte LP. CaMKK is an upstream signal of AMP-activated protein kinase in regulation of substrate metabolism in contracting skeletal muscle. Am J Physiol Regul Integr Comp Physiol 297: R1724-R1732, 2009. First published October 7, 2009; doi:10.1152/ajpregu.00179.2009.-Multiple signals have been shown to be involved in regulation of fatty acid (FA) and glucose metabolism in contracting skeletal muscle. This study aimed to determine whether a Ca2+-stimulated kinase, CaMKK, is involved in regulation of contraction-induced substrate metabolism and whether it does so in an AMP-activated protein kinase (AMPK)-dependent manner. Rat hindlimbs were perfused at rest (n = 16), with 3 mM caffeine (n = 15), with 2 mM 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR; n = 16), or during moderate-intensity muscle contraction (MC; n = 14) and with or without 5 mu M STO-609, a CaMKK inhibitor. FA uptake and oxidation increased (P < 0.05) 64% and 71% by caffeine, 42% and 93% by AICAR, and 65% and 143% by MC. STO-609 abolished (P < 0.05) caffeine- and MC-induced FA uptake and oxidation but had no effect with AICAR treatment. Glucose uptake increased (P < 0.05) 104% by caffeine, 85% by AICAR, and 130% by MC, and STO-609 prevented the increase in glucose uptake in caffeine and muscle contraction groups. CaMKK beta activity increased (P < 0.05) 113% by caffeine treatment and 145% by MC but was not affected by AICAR treatment. STO-609 prevented the caffeine- and MC-induced increase in CaMKK beta activity. Caffeine, AICAR, and MC increased (P < 0.05) AMPK alpha 2 activity by 295%, 11-fold, and 7-fold but did not affect AMPK alpha 1 activity. STO-609 decreased (P < 0.05) AMPK alpha 2 activity induced by caffeine treatment and MC by 60% and 61% but did not affect AICAR-induced activity. Plasma membrane transport protein content of CD36 and glucose transporter 4 (GLUT4) increased (P < 0.05) with caffeine, AICAR, and MC, and STO-609 prevented caffeine- and MC-induced increases in protein content. These results show the importance of Ca2+-dependent signaling via CaMKK activation in the regulation of substrate uptake and FA oxidation in contracting rat skeletal muscle and agree with the notion that CaMKK is an upstream kinase of AMPK in the regulation of substrate metabolism in skeletal muscle.