Acid phosphatase localization in endocytosed horizontal cell gap junctions.

Area of Science:

• Neuroscience
• Cell Biology
• Retinal Physiology

Background:

• Gap junction (GJ) endocytosis is implicated in GJ renewal in teleost fish retina horizontal cells.
• Three stages of GJ endocytosis (blebs, vesicles, lysosomal fusion) were previously identified via electron microscopy.

Purpose of the Study:

• To determine the stage at which enzymatic degradation begins for endocytosed GJs in white bass retina.
• To investigate the role of acid phosphatase (AP) in the degradative pathway of GJs.

Main Methods:

• Conventional electron microscopy (EM) was used.
• EM-level acid phosphatase (AP) histochemistry was performed on white bass retina.

Main Results:

• Electron-dense AP reaction product was found in the Golgi apparatus, mature lysosomes, and some internal GJ vesicles.
• GJ blebs, peripheral GJ vesicles, and most internal GJ vesicles lacked AP reaction product.
• AP was initially absent in GJ vesicles but acquired later, suggesting a degradative pathway.

Conclusions:

• Endocytosed GJ vesicles in retinal neurons are likely GJ endosomes on a degradative pathway.
• Degradation of GJs appears to initiate after vesicle formation, with AP acquired later.
• The precise role of GJ vesicle fusion with lysosomes in GJ degradation requires further investigation.