Acetonitrile as a substitute for ethanol/propylene oxide in tissue processing for transmission electron microscopy: comparison of fine structure and lipid solubility in mouse liver, kidney, and intestine.

Tissue processing for transmission electron microscopy (TEM) is commonly accomplished using ethanol (EtOH) as a dehydrating solvent and propylene oxide (PO) as a transition fluid. Both solvents have some undesirable properties: EtOH solubilizes lipids; PO is highly flammable, volatile, toxic, and potentially carcinogenic. Their replacement by a compound devoid of these characteristics is therefore desirable. Acetonitrile (AN) appears to be such a solvent. It is freely miscible with water, alcohols, acetone, and epoxy resins; it does not interfere with epoxy polymerization; and the resulting cured resins have excellent cutting quality and beam stability. AN is also an excellent dehydrating agent whose use does not necessitate modification of current techniques. Most importantly, the low solubility of phospholipids (PL) in AN limits the loss of membrane lipids and, hence, leads to a better preservation of tissue features.