Preservation of Actin Immunoreactivity in Paraffin Section by Tannic Acid Fixation on Chick Embryonic Heart: Comparison with Phalloidin Staining on Frozen Section

Degree of binding reactivity to actin in variously fixed tissues was histochemically examined by using phalloidin and antiactin staining on paraffin or frozen sections of 5-day chick embryonic heart. Fluorescein-labeled phalloidin staining on frozen section of the specimens fixed with 4% formaldehyde showed intense staining of actin in the myocardium and the aorticopulmonary (AP) septum. However, phalloidin did not react to actin on paraffin sections of the specimens fixed with 4% formaldehyde, nor fixed with 4% formaldehyde and 1% tannic acid (TA). FITC-labeled antiactin staining on paraffin sections of the specimens fixed with 4% formaldehyde and 1% TA showed comparable fluorescent intensity with that of phalloidin staining on frozen sections. However antiactin staining on paraffin sections of the specimens fixed with 4% formaldehyde only showed reduction of fluorescent intensity around the Ap septum. Both phalloidin and antiactin react non-specifically to the tissues fixed with solutions including 1% glutaraldehyde. Since paraffin sections showed much better tissue preservation than frozen sections, we suggest that paraffin embedding with TA fixation is very useful for actin histochemistry using antiactin.