A new selective ultrahistochemical method for the demonstration of calcium using N,N-naphthaloylhydroxylamine.

A new, simple, rapid, and highly sensitive and selective method for the ultrahistochemical detection of calcium is described. The reagent N,N-Naphthaloylhydroxylamine (1,8-C10H6CON(ONa)CO) sodium salt was employed in this study for the demonstration of calcium at the subcellular level in relaxed and contracted muscles (smooth muscle of the stomach, thoracic aorta, and myocardial muscle cells) of the rat (in vitro as well as in vivo) and in the human vascular smooth muscle of the aorta with atherosclerotic calcification. Direct evidence of the presence of calcium in the electron-dense reaction products (calcium N,N-Naphthaloylhydroxylamine) is given by X-ray microanalysis of 1,500-2,000 A thick sections. The significance of distributional differences in the localization of calcium in subcellular structures of relaxed and contracted muscles is discussed in relation to the role of calcium in the control of the muscle activity during the contraction-relaxation cycle.