Extracellular space markers
such as horseradish peroxidase and ruthenium
red have been used to clearly establish the
basolateral continuity of the tubular system and
its separation from the ER (Philpott, ’80). Pisam
and co-workers (’87) have made effective use of the
potassium ferrocyanide reduced osmium stain
developed by Karnovsky (’71) to unambiguously
differentiate the membrane elements of the
tubular system from the ER without the need
of extracellular markers.