MODULATION OF THE SUBCELLULAR-DISTRIBUTION OF CALMODULIN BY MELATONININ MDCK CELLS

In this paper we describe the interaction of melatonin with calmodulin in MDCK cells. The double staining immunofluorescent method showed th at calmodulin in control MDCK cells appeared as fluorescent spots at t he cell periphery. In contrast, MDCK cells cultured with 10(-9) M mela tonin for 6, 12, 24 hr or for 4 days showed that calmodulin fluorescen t spots were distributed throughout the cytoplasm as well as in the nu cleus. These calmodulin rearrangements were reversed 6 hr after melato nin withdrawal. Moreover, calmodulin radioimmunoassay showed that in 1 0(-9) M melatonin-treated cells, membrane-bound calmodulin content was increased by 78% whereas cytosolic calmodulin decreased by 60%. Simul taneous labeling of MDCK cells with specific antibodies against calmod ulin and melatonin showed that not only does the indole enter the cell , but that it has the same subcellular distribution as calmodulin. Bes ides the early responses induced by the melatonin antagonism to calmod ulin, the results suggest that the indole may also induce long-term ce llular responses by changing calmodulin concentrations in specific cel lular compartments.