Functional association between nicotinic acetylcholine receptor and sarcomeric proteins via actin and desmin filaments

By affinity chromatography utilizing alpha-cobrotoxin from digitonin-solubi lized fractions of rabbit skeletal muscle, we found that many proteins are associated with the nicotinic acetylcholine receptor (AChR). In addition to the proteins we previously reported to bind to AChR (including dystrophin- dystrophin-associated protein (DAP) complex, utrophin, rapsyn, and actin; M itsui et at. [1996] Biochem. Biophys. Res. Commun.224:802-807), alpha-actin in, desmin, myosin, tropomyosin, troponin T, and titin are also identified to be associated with AChR. Alkaline treatment or Triton X-100 solubilizati on released dystrophin-DAP complex, utrophin, and rapsyn from the AChR frac tion, while actin and desmin remained associated. These findings demonstrat e that AChR is supported primarily by a submembranous organization of actin and desmin filaments, and is linked to sarcomeric proteins via these filam ents. To Further investigate whether the association has any functional rol e, we studied the effect of acetylcoline on ATPase activity of the AChR fra ction. Acetylcholine (0.5-4 mu M) significantly activated Mg2+-ATPase activ ity of digitonin-solubilized AChR fraction (P < 0.05). Furthermore, we foun d that desmin as well as actin activated myosin Mg2+-ATPase activity. From these findings, it is suggested that desmin and actin form a submembranous organization in the postsynaptic region, and function as mediators of excit ation of AChR to the sarcomeric contraction system, J. Cell. Biochem. 77: 5 84-595,2000. (C) 2000 Wiley-Liss, Inc.