Knockout of the predominant conventional PKC isoform, PKCα, in mouse skeletal muscle does not affect contraction-stimulated glucose uptake

Jensen TE, Maarbjerg SJ, Rose AJ, Leitges M, Richter EA. Knockout of the predominant conventional PKC isoform, PKC alpha, in mouse skeletal muscle does not affect contraction-stimulated glucose uptake. Am J Physiol Endocrinol Metab 297: E340-E348, 2009. First published May 19, 2009; doi: 10.1152/ajpendo.90610.2008.-Conventional (c) protein kinase C (PKC) activity has been shown to increase with skeletal muscle contraction, and numerous studies using primarily pharmacological inhibitors have implicated cPKCs in contraction-stimulated glucose uptake. Here, to confirm that cPKC activity is required for contraction-stimulated glucose uptake in mouse muscles, contraction-stimulated glucose uptake ex vivo was first evaluated in the presence of three commonly used cPKC inhibitors (calphostin C, Go r-6976, and Go r-6983) in incubated mouse soleus and extensor digitorum longus (EDL) muscles. All potently inhibited contraction-stimulated glucose uptake by 50-100%, whereas both Go compounds, but not calphostin C, inhibited insulin-stimulated glucose uptake modestly. AMP-activated protein kinase (AMPK) and eukaryotic elongation factor 2 phosphorylation was unaffected by the blockers. PKC alpha was estimated to account for similar to 97% of total cPKC protein expression in skeletal muscle. However, in muscles from PKC alpha knockout (KO) mice, neither contraction-nor phorbol ester-stimulated glucose uptake ex vivo differed compared with the wild type. Furthermore, the effects of calphostin C and Go r-6983 on contraction-induced glucose uptake were similar in muscles lacking PKC alpha and in the wild type. It can be concluded that PKC alpha, representing similar to 97% of cPKC in skeletal muscle, is not required for contraction-stimulated glucose uptake. Thus the effect of the PKC blockers on glucose uptake is either nonspecific working on other parts of contraction-induced signaling or the remaining cPKC isoforms are sufficient for stimulating glucose uptake during contractions.