PRESERVATION OF Na-K-ACTIVATED AND Mg-ACTIVATED ADENOSINE TRIPHOSPHATASE ACTIVITIES OF AVIAN SALT GLAND AND TELEOST GILL WITH FORMALDEHYDE AS FIXATIVE

The effect of glutaraldehyde and formaldehyde fixation on the level of biochemically demonstrable Na-K-adenosine triphosphatase (Na-K-ATPase) and Mg-ATPase of avian salt glands and teleost gill filaments was studied. Sections, 100-200 µ, prepared with the Smith-Farquhar tissue chopper, were fixed for varying periods, homogenized and assayed for ATPase activity. Fixation of salt gland tissue with 0.5% glutaraldehyde for 40-60 min completely inhibited the Na-K-ATPase activity and reduced the level of Mg-ATPase by 85%. In contrast, fixation with 2 or 3% formaldehyde, prepared from paraformaldehyde, for 60-90 min resulted in a loss of only 30% of the Na-K-ATPase activity and 65% of the Mg-ATPase activity. Similar results were obtained with gill filaments. In addition, Na-K-ATPase of formaldehyde-fixed tissue retained an obligatory requirement for Na + and K + and was fully sensitive to ouabain. Electron microscopic examination of formaldehyde-fixed tissue, sectioned with either the tissue chopper or in the cryostat and incubated in the Wachstein-Meisel medium, showed excellent morphologic preservation. Reaction product deposition (presumably due to Mg-ATPase) was associated with the extracellular side of the plasma membrane in the secretory cells of the salt gland and over the mitochondrial matrix of chloride cells present in the gill epithelium.