[Cyclic adenosine monophosphate and the enzyme activity of its metabolism in L cells sensitive and resistant to the cytotoxic action of ethidium bromide].

Using L-cells both sensitive and resistant to cytotoxic action of ethidium bromide (EB), a study was made of the intracellular level of cAMP, activities of adenylcyclase, phosphodiesterase and cAMP, liberated from cells into the surrounding medium. In EB resistant L-cells compared to EB sensitive ones, the higher level of cAMP with a decreased activity of adenylcyclase and an increased activity of the phosphodiesterase was shown to be associated with an impeded exit of cAMP from cells. It is suggested that the differences in cAMP levels in the EB sensitive and resistant cells are associated with the properties of cAMP-dependent protein kinases of these cells.