Different aspects of membrane differentiation at the inner side (GERL) of the Golgi apparatus in rabbit luteal cells.

After luteinization, during the growth phase, rabbit luteal cells showed a well-developed Golgi apparatus, which was clearly reduced at the end of pseudo-pregnancy. During this whole period, acid phosphatase was demonstrated in the saccules (g) of the Golgi stack and in the innermost Golgi element (G2), which may be part of GERL. Between both acid phosphatase-positive compartments, a negative or slightly positive element (G1) was present paralleling the saccules of the Golgi stack. This element was composed of cisternal (G1 c) and perforated portions (G1 p) and directly bordered the thiamine pyrophosphatase-positive saccules of the Golgi stack (g1 -g2). Arylsulphatase activity was present in two saccules in the middle of the stack (g3 -g4) and in the innermost Golgi element (G2). In the acid phosphatase and arylsulphatase reactions the limiting membrane of the lysosomes was more reactive than the matrix. After phosphotungstic acid staining at a low pH, the inner elements of the Golgi apparatus (G1 and G2) and the border of the lysosomes were heavily contrasted. The lysosomal matrix and the other Golgi stack saccules were either almost unstained or displayed a clearly lower contrast. It is concluded that the cytochemical difference between Golgi (g) and GERL (G) membranes is most probably the result of a specific process of membrane differentiation, which takes place at G1. There is also evidence that the lysosomal matrix hydrolases may be formed in the saccules of the Golgi stack. The strongly phosphotungstic acid-positive inner elements are, although more extended, comparable in large part with the GERL elements as described in neurons (Novikoff et al., 1971).