This study was designed to examine activity of AMP-activated protein kinase kinase (AMPKK) and AMP-activated protein kinase (AMPK) in muscles from control (C) and endurance trained (T) rats. Rats were trained 5 days/wk, 2 hr/d for 8 wks at a final intensity of 32 m/min up a 15% grade with 30 second sprints at 52 m/min every 10 min. Gastrocnemius muscles were stimulated in situ in T and C rats for 5 min at frequencies of 0.4/sec and 1/sec. Gastrocnemius LKB1 protein, a putative component of the AMPKK complex (LKB1, STRAD, and MO25), increased approximately 2-fold in response to training. Phosphorylation of AMPK determined by western blot was increased at both stimulation rates in both control and trained rats. AMPK activity of both the α1 and α2 isoforms (immunoprecipitates) also increased at both stimulation rates in both C and T rats. AMPKK activity was strikingly lower in both resuspended polyethylene glycol (PEG) precipitates and 1200 x g supernatant of the crude homogenate of muscle extracts from the trained compared to control rats. AMPKK activity did not increase in either T or C in response to electrical stimulation even though phospho-AMPK did increase. Interestingly, AMPKK activity in the 1200 x g supernatant of the crude homogenate actually decreased upon stimulation in the control rats. These results suggest that AMPKK is activated during electrical stimulation by mechanisms other than covalent modification. Possibilities include AMP-induced optimization of the phosphorylation site on the target protein, contraction-induced changes in undefined allosteric modulators, and contraction-induced association with other proteins. (Study approved by the IACUC and supported by NIH RO1 AR41438.)



College and Department

Life Sciences; Physiology and Developmental Biology



Date Submitted


Document Type





AMPK, LKB1, AMP-activated protein kinase, AMPKK