The distribution of orthogonal assemblies and other intercalated particles in frog sartorius and rabbit sacrospinalis muscle.
Freeze-fracture replicas have been prepared from two fast-acting vertebrate muscles (frog sartorius and rabbit sacrospinalis) and are described with particular reference to the distribution of intercalated particles in the plasma membrane. T-tubule and SR cisternae. Orthogonal assemblies of small particles are present on the A face plasma membrane in each instance, and their distribution (in sartorius) is found to be random with respect to the underlying myofibrillar sarcomere repeat. Such assemblies are not present on A or B faces of T-tubule or SR cisternae. Asymmetric particle distribution is described for fracture faces of the T-tubules and SR: the profuse particle packing of the SR A face is uniform from terminal cisternae to medial fenestrated collar. Intercalated particles are present on A and B faces of T-tubule fractures; more commonly on the latter. These results are compared with studies on insect muscles, and a comparative approach to further studies on the correlation between membrane structure and function is discussed.
D000818:Animals; D001001:Anura; D002462:Cell Membrane / Q000648:ultrastructure; D005614:Freeze Fracturing; D008870:Microtubules / Q000648:ultrastructure; D009132:Muscles / Q000648:ultrastructure*; D010316:Particle Size; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure