Phorbol 12-myristate 13-acetate modulates the cAMP-induced light-scattering response of a Dictyostelium discoïdeum cell population

The effect of phorbol 12-myristate 13-acetate upon the light-scattering response to cAMP of a D. discoïdeum cell suspension was investigated. It was found that the first spike of the cAMP-mediated light-scattering change (peaking at about 15–20 s after stimulation) was inhibited by the phorbol ester. This effect was concentration dependent with an half-maximum value for the inhibition of 4 nM. The inhibition was found to be maximal after a 10–20 min incubation time. The phorbol ester was shown to affect the dose-response relationship between the cAMP concentration and the relative amplitude of the light-scattering change, more by decreasing the number of cAMP receptors than by decreasing their apparent affinity for cAMP.