Organelle-free cytoplasmic volume fraction of rabbit retinal Müller (glial) cells.

Retinal Müller (glial) cells are thought to act as "cables" carrying spatial buffering K+ currents from the sites of neuronal release into the reservoir of the vitrous body. In order to calculate the amplitude of such currents it is necessary to know the intracellular volume fraction which is able to carry these currents. Thus, this organelle-free volume fraction was measured in transmission electron microscopic photograms of rabbit Müller cells. This volume fraction was found to vary between 0.7 and more than 0.9 in various retinal layers except at the "external limiting membrane" where it was reduced to 0.24 by the accumulation of mitochondria. In enzymatically isolated cells all values are slightly increased by cell swelling.