Reciprocity between tissue calmodulin and cAMP levels: modulation by excess zinc

Signal transduction of many intracellular events is initiated by a minute influx of calcium ions into the cells, resulting in the formation of calcium-calmodulin complex and cAMP. Because zinc appears to have an inhibitory effect on a number of tissue reactions, it is postulated that this occurs through modulation of intracellular calcium influx. To test the hypothesis that the inhibitory effects of zinc are mediated through the calcium-calmodulin-cAMP pathway, zinc was administered by various routes to five groups of nude mice (control, intragastric, intraperitoneal, intradermal and oral groups), and calmodulin and cAMP concentrations were measured in the cytosol of epidermal cells. Calmodulin levels decreased significantly in the groups given intraperitoneal zinc (P<0.025) and intradermal zinc (P<0.001) injections. Significant elevations of cAMP levels were noted with intradermal zinc (P<0.025). Overall, the relationship between calmodulin and cAMP appeared to be inversely logarithmic, with the lowest calmodulin levels associated with the highest cAMP concentrations. In addition, there was a significant trend towards a smaller calmodulin/cAMP ratio in all zinc-treated groups, except the mice fed dietary zinc. These results appear to correlate with tissue zinc levels obtained with these various forms of zinc administration. Our results therefore indicate that there is a reciprocity between epidermal calmodulin and cAMP levels, which may be modulated by external factors such as zinc.