The organization of the Golgi complex and microtubules in skeletal muscle is fiber type-dependent

Skeletal muscle has a nonconventional Golgi complex (GC), the organization of which has been a subject of controversy in the past. We have now examine d the distribution of the GC by immunofluorescence and immunogold electron microscopy in whole fibers from different rat muscles, both innervated and experimentally denervated. The total number of GC elements, small polarized stacks of cisternae, is quite similar in all fibers, but their intracellul ar distribution is fiber type-dependent. Thus, in slow-twitch, type I fiber s, similar to 75 of all GC elements are located within 1 mu m from the plas ma membrane, and each nucleus is surrounded by a belt of GC elements. In co ntrast, in the fast-twitch type IIB fibers, most GC elements are in the fib er core, and most nuclei only have GC elements at their poles. Intermediate , type IIA fibers also have an intermediate distribution of GC elements. In terestingly, the distribution of microtubules, with which GC elements coloc alize, is fiber type-dependent as well. At the neuromuscular junction, the distribution of GC elements and microtubules is independent of fiber type, and junctional nuclei are surrounded by GC elements in all fibers. After de nervation of the hindlimb muscles, GC elements as well as microtubules conv erge toward a common pattern, that of the slow-twitch fibers, in all fibers . Our data suggest that innervation regulates the distribution of microtubu les, which in turn organize the Golgi complex according to muscle fiber typ e.