Chicken dystrophy. The geometry of the transverse tubules.

The pectoral muscle of chickens afflicted with muscular dystrophy, when examined with the electron microscope, contains a) numerous, often quite large vesicles with and without caveolar evaginations, b) tubules with caveolar evaginations, and c) tubular networks. We have demonstrated that all these structures are derivatives of the transverse tubles as revealed by tracer studies and freeze-fracture complementary replicas. The membranes of transverse tubular origin show a small number of intramembranous particles on both P and E faces with no complementary geometry. The membranes of the free sacrcoplasmic reticulum (SR) and the junctional SR of normal and dystrophic muscle appear identical in complementary freeze-fracture replicas. Vesicles that carry only a small number of particles on both E and P faces exposed by freeze-fracturing in isolated SR preparations can be taken as presumptive evidence and serve as a morphologic marker for transverse tubular origin of such vesicles when mitochondrial and lysosomal contamination has been excluded.