Cyclic AMP effects on cell-to-cell junctional membrane permeability during adipocyte differentiation of 3T3-L1 fibroblasts.

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Abstract
Mouse 3T3-L1 fibroblast cells, also known as preadipocytes, differentiate in vitro into adipocytes when treated with promoting agents and acquire numerous properties characteristic of mature fat cells. Junctional cell-to-cell communication was studied by measuring the incidence of electrical coupling and transfer of carboxy-fluorescein among these cells. When 3T3-L1 cells were induced to differentiate into adipocytes, they lost virtually all cell-cell communication. Preadipocytes that remained nondifferentiated after the treatment maintained normal communication. Loss of communication in the adipocytes invariably coincided with appearance of lipid droplets and not with other phenotypic changes. In the differentiating cells, loss of cell-to-cell communication and lipid accumulation was prevented if dibutyryl cAMP and caffeine were present in the culture medium. Addition of dibutyryl cAMP and caffeine to already differentiated adipocytes resulted in loss of lipid and simultaneously improved junctional permeability. In the in vitro 3T3-L1 cell system, cell-to-cell communication and lipid synthesis are intimately related during the adipose conversion and cAMP affects the expression of the 2 phenotypes.