Junctional subsurface organs in frog sympathetic ganglion cells.

Subsurface cisternae in frog sympathetic ganglion cells were studied and shown to have similar features to those of the C.N.S. A number of special features were, however, revealed by high resolution microscopy. Highly flattened subsurface cisternae occurred in close proximity to the ganglion cell membrane and formed structures comparable to gap junctions. These subsurface cisternae appeared to be elongated plates (about 0.3 X 2.5 mum) specifically restricted to the area of the ganglion cell membrane adjacent to nerve endings, although often with the intervention of a thin satellite sheath. Thus they have been termed here 'junctional subsurface organs', although the nerve terminals opposing them did not show any synaptic specialization. The junctional subsurface organ was often accompanied by closely arrayed endoplasmic reticulum and/or mitochondria. Where the junctional subsurface organ intervened between plasma membrane and endoplasmic reticulum or mitochondria, faint particles appeared to traverse both sides and bridge the narrow spaces to the opposing plasma membrane and endoplasmic reticulum or mitochondria. The possible functional significance of the junctional subsurface organs is discussed.