Effects of prostaglandins and divalent cations on cAMP production in isolated rat hepatocytes

In intact hepatocytes, prostaglandin E2 (PGE2) inhibits up to 60% of the cyclic AMP (cAMP) formation in response to glucagon. PGE2 was found also to inhibit cAMP production in response to Mn2+, and Mn2+ counteracted the effect of PGE2 on the response to glucagon. However, when added to cells with ruptured plasma membranes, PGE2 had no effect on cAMP production, even though the ruptured cells had an equally strong response to glucagon as did intact cells. Only when cells were ruptured in the presence of PGE2 and incubated as very dense suspensions did PGE2 inhibit a response to glucagon up to 20%. These results may be explained by assuming the existence of a cytosolic factor necessary for transmitting the inhibitory effect of PGE2. The role of divalent cations in cAMP formation in intact cells was investigated. After extraction of cations with ethylenediamine-tetraacetic acid (EDTA), cAMP production in response to glucagon was reduced by more than 60%. Addition of Mn2+ restored cAMP formation completely, whereas Mg2+ was somewhat less effective, and Ca2+ could not restore any activity. Even low concentrations of Ca2+ appeared under certain conditions to repress adenylate cyclase activity.