Contraction stimulates muscle glucose uptake independent of atypical PKC

Abstract

Exercise increases skeletal muscle glucose uptake, but the underlying mechanisms are only partially understood. The atypical protein kinase C (PKC) isoforms λ and ζ (PKC-λ/ζ) have been shown to be necessary for insulin-, AICAR-, and metformin-stimulated glucose uptake in skeletal muscle, but not for treadmill exercise-stimulated muscle glucose uptake. To investigate if PKC-λ/ζ activity is required for contraction-stimulated muscle glucose uptake, we used mice with tibialis anterior muscle-specific overexpression of an empty vector (WT), wild-type PKC-ζ (PKC-ζWT), or an enzymatically inactive T410A-PKC-ζ mutant (PKC-ζT410A). We also studied skeletal muscle-specific PKC-λ knockout (MλKO) mice. Basal glucose uptake was similar between WT, PKC-ζWT, and PKC-ζT410A tibialis anterior muscles. In contrast, in situ contraction-stimulated glucose uptake was increased in PKC-ζT410A tibialis anterior muscles compared to WT or PKC-ζWT tibialis anterior muscles. Furthermore, in vitro contraction-stimulated glucose uptake was greater in soleus muscles of MλKO mice than WT controls. Thus, loss of PKC-λ/ζ activity increases contraction-stimulated muscle glucose uptake. These data clearly demonstrate that PKC-λζ activity is not necessary for contraction-stimulated glucose uptake.