EVIDENCE THAT MULLER CELLS CAN PHAGOCYTIZE EGG-LECITHIN-COATED SILICONE PARTICLES

This study is designed to better understand the function of the Muller cells of the retina through the use of silicon particles that had been injected into the vitreous body of the eye and via an analysis of the number of gap junctions associated with these cells. Following intraocular injection of a silicone oil mixture into the rabbit retina, numerous small silicone particles less than 1 mum in diameter were found attached to the basement membrane of the inner limiting membrane, subjacent to the Muller cells. On the sites to which the silicone particles attached, the basement membrane was reduced in thickness or completely disappeared. The 'end-feet' of the cell membrane facing the silicone particles became concave appearing as if they were in the process of incorporating the particles into the cell. Similarly, the Muller cells occasionally extended cytoplasmic processes through the basement membrane and towards the silicone particles, as if to engulf them. Gap junctions were observed but only in association with the Mullet cells. They were often found between the 'end-feet' of adjacent Muller cells or the 'end-feet' of one cell and very thin cytoplasmic process of a neighboring cell. On rare occasions, they were located between 'end-feet' of the same Muller cell, The percentage of 'end-feet' displaying gap junctions was 38 +/- 8% (mean +/- SE). These data suggest that the Muller cells are important in the maintenance of normal retinal function by their ability to phagocytize foreign substances and by their ability to transmit information to various parts of the retina through cell-to-cell connections established by gap junctions.