Activation of p38 mitogen-activated protein kinase alpha and beta by insulin and contraction in rat skeletal muscle - Potential role in the stimulation of glucose transport

The stress-activated p38 mitogen-activated protein kinase (MAPK) was recent ly shown to be activated by insulin in muscle and adipose cells in culture. Here, we explore whether such stimulation is observed in rat skeletal musc le and whether muscle contraction can also affect the enzyme. Insulin injec tion (2 U over 3.5 min) resulted in increases in p38 MAPK phosphorylation m easured in soleus (3.2-fold) and quadriceps (2.2-fold) muscles. Increased p hosphorylation (3.5-fold) of an endogenous substrate of p38 MAPK, cAMP resp onse element binder (CREB), was also observed. After in vivo insulin treatm ent, p38 MAPK alpha and p38 MAPK beta isoforms were found to be activated ( 2.1- and 2.4-fold, respectively), using an in vitro kinase assay, in immuno precipitates from quadriceps muscle extracts. In vitro insulin treatment (1 nmol/l over 4 min) and electrically-induced contraction of isolated extens or digitorum longus (EDL) muscle also doubled the kinase activity of p38 MA PK alpha and p38 MAPK beta. The activity of both isoforms was inhibited in vitro by 10 mu mol/l SB203580 in all muscles. To explore the possible parti cipation of p38 MAPK in the stimulation of glucose uptake, EDL and soleus m uscles were exposed to increasing doses of SB203580 before and during stimu lation by insulin or contraction. SB203580 caused a significant reduction i n the insulin- or contraction-stimulated 2-deoxyglucose uptake. Maximal inh ibition (50-60%) occurred with 10 mu mol/l SB203580, These results show tha t p38 MAPK alpha and -beta isoforms are activated by insulin and contractio n in skeletal muscle. The data further suggest that activation of p38 MAPK may participate in the stimulation of glucose uptake by both stimuli in rat skeletal muscle.