Independent regulation of the extracellular cyclic AMP phosphodiesterase-inhibitor system and membrane differentiation by exogenous cyclic AMP in Dictyostelium discoideum☆

摘要

WhenamoebaeofDictyosteliumdiscoideum,suspendedinbuffer,weretreatedwith100nMpulsesofcAMP,theextracellularcAMPphosphodiesterase(ePD)activityincreaseddramaticallyandthesynthesisofthephosphodiesteraseinhibitor(PDI)wasrepressed.Inaddition,thetimeofappearanceonthecellsurfaceofcontactsitesA,membrane-boundcAMPphosphodiesterase,andcAMPbindingsiteswasacceleratedby3a€“4hrandtheconcentrationofintracellularcAMPincreaseda??20-fold.WhentheconcentrationofthecAMPpulsewasreducedto1nM,theeffectofthepulsesonmembranedifferentiationandonthecAMPpoolwasvirtuallythesame,whiletheeffectontheePD-PDIsystemwasreduced.WhencAMPwasaddedtothesuspensioncontinuously,thenucleotidehadnoeffectonmembranedifferentiationandfailedtostimulatetheintracellularcAMPpool,however,theePD-PDIsystemwasregulatednormally.Whenthedevelopmentalmutant,HC112,wastreatedwithcAMPpulses,membranedifferentiationandthelevelofthecAMPpoolwereunaffected,whiletheePD-PDIsystemrespondedtotheexogenouscAMP.Inanothermutant,HC53,membranedifferentiationwasstimulatedbycAMPpulsesandthisresponsewasaccompaniedbyasharpincreaseintheconcentrationofthecAMPpool.TheseresultssuggestthattheePD-PDIsystemandmembranedifferentiationareregulatedindependentlybyexogenouscAMPandthatregulationoftheePD-PDIsystemdoesnotrequireactivationoftheadenylylcyclase.