Synaptic vesicle retrieval in central nerve terminals can occur via at least two different pathways, fast and slow endocytosis. Slow endocytosis is only activated by strong physiological stimulation and the molecules that trigger and mediate this process are still being identified. We have recently shown that the phosphorylation cycle of the group of proteins called the dephosphins selectively control the slow endocytic pathway in central nerve terminals. One of the dephosphins is the large GTPase dynamin I, whose dephosphorylation is essential for at least one form of synaptic vesicle endocytosis. The dephosphorylation of dynamin I allows an interaction with the endocytosis protein syndapin I, placing syndapin I as the possible effector in slow endocytosis. Thus the dephosphins may be key sensors for activation of slow endocytosis during strong stimulation.