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

Abstract

When amoebae of Dictyostelium discoideum, suspended in buffer, were treated with 100 n M pulses of cAMP, the extracellular cAMP phosphodiesterase (ePD) activity increased dramatically and the synthesis of the phosphodiesterase inhibitor (PDI) was repressed. In addition, the time of appearance on the cell surface of contact sites A, membrane-bound cAMP phosphodiesterase, and cAMP binding sites was accelerated by 3–4 hr and the concentration of intracellular cAMP increased ⋍20-fold. When the concentration of the cAMP pulse was reduced to 1 n M, the effect of the pulses on membrane differentiation and on the cAMP pool was virtually the same, while the effect on the ePD-PDI system was reduced. When cAMP was added to the suspension continuously, the nucleotide had no effect on membrane differentiation and failed to stimulate the intracellular cAMP pool, however, the ePD-PDI system was regulated normally. When the developmental mutant, HC112, was treated with cAMP pulses, membrane differentiation and the level of the cAMP pool were unaffected, while the ePD-PDI system responded to the exogenous cAMP. In another mutant, HC53, membrane differentiation was stimulated by cAMP pulses and this response was accompanied by a sharp increase in the concentration of the cAMP pool. These results suggest that the ePD-PDI system and membrane differentiation are regulated independently by exogenous cAMP and that regulation of the ePD-PDI system does not require activation of the adenylyl cyclase.