Immunohistological localization of calmodulin in feline rod outer segments

The calcium-binding regulatory protein, calmodulin, was immunohistologically examined in feline rod outer segments. The peroxidase antiperoxidase technique was used for the immunohistological analysis and protein A-gold, to localize calmodulin electron-microscopically. Calmodulin was found to be located in the distal position of the rod outer segments. Most of the gold particles could be seen on the disk membranes. The same observations were obtained for retinas in either a light or dark environment. Thus, there is the possibility that calmodulin may have some influence on enzyme activity in the rod outer segments, particularly in the distal portion.