van Ments-Cohen M, Genieser H G, Jastorff B, Van Haastert P J, Schaap P
Cell Biology and Genetics Unit, University of Leiden, The Netherlands.
FEMS Microbiol Lett. 1991 Jul 15;66(1):9-14. doi: 10.1016/0378-1097(91)90412-4.
Dictyostelium cells exhibit four types of kinetically distinct surface cAMP binding sites, the AH, AL, BS, and BSS sites, which are down-regulated during persistent stimulation with cAMP. Although most cAMP-induced responses are subject to desensitization during constant stimulation, some responses, notably the induction of post-aggregative gene expression, require persistent cAMP stimulation. The kinetics and specificity of residual cAMP-binding activity in cells treated for 4 h with micromolar cAMP were investigated. It was found that around 4000 rapidly dissociating binding sites per cell with an affinity of about 300 nM are retained after down-regulation. The nucleotide specificity of the remaining sites was very similar, but not completely identical to the AH, AL and B sites, suggesting that these sites belong to the same class of cell surface cAMP receptors and may be utilized to mediate responses requiring continuous cAMP stimulation.
