Dark-induced changes in activity and compartmentalization of retinal calmodulin kinase in the rat.

Calmodulin kinase (CaM kinase) activity and immunoreactivity were measured in the cytosol and crude synaptic membranes of light- and dark-adapted rat retinas. Dark adaptation increased the calcium-independent CaM kinase activity 2.7 times and calcium-stimulated activity 3.9 times in membrane fractions. Dark adaptation also increased membrane-bound CaM kinase immunoreactivity 2.4 times. In the cytosol, dark adaptation increased calcium- and calmodulin-independent kinase activity 3.3-fold but did not enhance calcium- and calmodulin-dependent activity. Soluble CaM kinase immunoreactivity was decreased by 13% by dark exposure. These changes in enzyme activity and immunoreactivity are likely due to changes in the endogenous state of autophosphorylation and compartmental concentrations of CaM kinase and may represent translocation of CaM kinase from cytosol to membranes. CaM kinase may have an important role in modulating visual processes.