Comparison of various methods to localize a source of radioactivity in ultrastructural autoradiographs. The site of [3H]-galactose incorporation in surface mucous cells of the rat stomach.

Abstract

Three methods of Ag-grain quantitation in autoradiographs were applied to localize the site of [3H]galactose in surface mucous cells of the rat stomach: the method of direct allocation, the probability-circle method and the method of band-source distribution. Methods I and II showed the Golgi system to be the almost exclusive site of galactose attachment. The greater complexity of the circle method (II) relative to the method of direct allocation (I) was not justified. Since the subdivisions of the Golgi system are small and inhomogenous and display 2 or more other structures when showing up in the probability circles, they do not meet the conditons for optimal utilization of the resolving capacity of method II. Nevertheless it was from method II that the site of highest radioactivity was assigned to the trans half of the Golgi stacks. With photographs of selected Golgi systems at 2.5-fold higher magnification, method I also indicated the trans half of the Golgi stack as the site of highest radioactivity. Using method III, the distribution of Ag-grain densities on both sides of the trans front of these selected Golgi stacks was compared with calculated density distributions around line and band sources belonging to various models. The observed distribution fits (P < 0.005) a model that localizes at least 91% of Golgi radioactivity in the 2 trans cisternae of the stacks, confirming the suggestions from methods I and II. Method III, because of the simple geometric form of the Golgi stacks, gave the most exact information as to the site of [3H]galactose in the Golgi system.