ABSTRACT
Protein phosphorylation plays an essential role in regulating synaptic transmission and plasticity. However, regulation of vesicle trafficking towards and away from the plasma membrane is poorly understood. Furthermore, the extent to which phosphorylation modulates ribbon-type synapses is unknown. Using the phosphatase inhibitor okadaic acid (OA), we investigated the influence of persistent phosphorylation on vesicle cycling in goldfish bipolar cells. We followed uptake of FM1-43 during vesicle recycling in control and OA-treated cells. FM1-43 fluorescence spread to the center of control synaptic terminals after depolarization elicited Ca2+ influx. However, OA (1-50 nm) impaired this spatial spread of FM1-43 in a dose-dependent manner. Capacitance measurements revealed that OA (50 nm) did not modify either the amount or kinetics of exocytosis and endocytosis evoked by depolarizing pulses. The extremely low concentrations of OA (1-5 nm) sufficient to observe the inhibition of vesicle mobility implicate phosphatase 2A (PP2A) as a major regulator of vesicle trafficking after endocytosis. These results contrast with those at the neuromuscular junction where OA enhances lateral movement of vesicles between distinct vesicle clusters. Thus, our results suggest that phosphatases regulate vesicle translocation at ribbon synapses in a different manner than conventional active zones.
Subject(s)
Enzyme Inhibitors/pharmacology , Okadaic Acid/pharmacology , Retina/physiology , Synapses/metabolism , Synaptic Vesicles/metabolism , Animals , Biological Transport/drug effects , Calcium/metabolism , Cell Membrane/metabolism , Cell Separation , Dose-Response Relationship, Drug , Electric Capacitance , Electric Stimulation , Endocytosis/drug effects , Exocytosis/drug effects , Fluorescent Dyes/pharmacokinetics , Goldfish , In Vitro Techniques , Patch-Clamp Techniques , Pyridinium Compounds/pharmacokinetics , Quaternary Ammonium Compounds/pharmacokinetics , Retina/cytology , Retina/drug effects , Synapses/drug effects , Synaptic Transmission/drug effectsABSTRACT
Os autores tecem comentários sobre a farmacocinética dos bloqueadores neuromusculares adespolarizantes e despolarizantes, enfatizando principalmente os aspectos da fisiopatologia que podem alterá-la, como a gravidez, hipotermia, idade avançada e insuficiência renal e hepática