Pannexin 1 and pannexin 3 channels regulate skeletal muscle myoblast proliferation and differentiation.
Bottom Line: Using HSMM, we found that Panx1 expression promotes this process, whereas it was impaired in the presence of probenecid or carbenoxolone.As for Panx3, its lower molecular weight species were prominent in adult skeletal muscle but very low in the fetal tissue and in undifferentiated skeletal muscle cells and myoblasts.On the other hand, a ∼70-kDa immunoreactive species of Panx3, likely glycosylated, sialylated, and phosphorylated, was highly expressed in proliferative myoblasts but strikingly down-regulated during their differentiation.
Affiliation: From the Department of Surgery, Division of Paediatric Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada, Apoptosis Research Center, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada.Show MeSH
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Mentions: Panx1 transcripts were found strongly expressed in human skeletal muscle (24). At the protein level, Western blot analysis from Riquelme et al. (26) showed different molecular weight species of Panx1 in rat muscle, and immunolocalization studies suggested that Panx1 is located at the sarcolemma and at the T-tubules of adult mice and rat fibers (25, 26). In the current study we initially wanted to confirm the presence of Panx1 in this tissue and also determine whether Panx2 and Panx3 are present in the skeletal muscle of human, rat, and mouse by Western blot analysis. As shown in Fig. 1A, Panx1 antibodies recognized several species (mainly at ∼38–50 kDa) in human, mouse, and rat skeletal muscle tissue, most likely reflecting various degrees of glycosylation. A similar banding pattern for endogenous Panx1 has been detected in many murine organs (∼41–48 kDa) (3) and as multiple species of ∼43–50 kDa in the rat skeletal muscle (26). As shown in Fig. 1A, Panx3 antibodies also recognized several bands in human, mouse, and rat skeletal muscle. All three species express multiple glycosylated forms at ∼43 kDa. Human and mouse skeletal muscle also show the presence of a band at ∼70 kDa. The presence of a Panx3 immunoreactive species at a similar molecular weight (Mr) has also been reported in several murine organs (3), murine skin (6), and organotypic epidermis (7) and in the rat male reproductive tract (8). However, that band was very low or below detectable levels in rat tissue. An additional band at ∼51 kDa was strongly detected by anti-Panx3 in the human skeletal muscle lysate. A similar band has been previously detected in the murine kidney (3). These data differ from that of Riquelme et al. (26) reporting that Panx3 is absent in skeletal muscle and may be explained by the use of different Panx3 antibodies. On the other hand, Panx2 was not detected in human, mouse, or rat skeletal muscle lysates (Fig. 1A). Skeletal muscles present within human skin sections were then labeled for Panx1 and Panx3. Interestingly, Panx1 was detected as punctate structures, but Panx3 stained diffusely throughout the skeletal muscle fibers and showed striations at higher magnification (Fig. 1B). Panx1 and Panx3 labeling were specific as incubation with secondary antibodies alone (data not shown) as well as peptide competition experiments (Fig. 1B) abrogated any positive staining. The difference in Panx1 and Panx3 immunolabeling seen here may suggest different functions within the skeletal muscle tissue.
Affiliation: From the Department of Surgery, Division of Paediatric Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada, Apoptosis Research Center, Children's Hospital of Eastern Ontario, Ottawa, Ontario K1H 8L1, Canada.