THE ACTIVATION OF PROTEIN-KINASE A PATHWAY SELECTIVELY INHIBITS ANTEROGRADE AXONAL-TRANSPORT OF VESICLES BUT NOT MITOCHONDRIA TRANSPORT OR RETROGRADE TRANSPORT IN-VIVO

To shed light on how axonal transport is regulated, we examined the po ssible roles of protein kinase A (PKA) in vivo suggested by our previo us work (Sato-Yoshitake et al., 1992), Pharmacological probes or the p urified catalytic subunit of PKA were applied to the permeabilized-rea ctivated model of crayfish walking leg giant axon, and the effect was monitored by the quantitative video-enhanced light microscopy and the quantitative electron microscopy, Dibutyryl cyclic AMP caused concentr ation-dependent transient reduction in the number of anterogradely tra nsported small vesicles, while the retrogradely transported organelles and anterogradely transported mitochondria showed no decrease, This t ransient selective inhibition of anterograde vesicle transport was rev ersed by the application of a specific inhibitor of PKA (KT5720) in a concentration-dependent manner, and was reproduced by the application of the purified catalytic subunit of PKA and augmented by the applicat ion of adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S). Correspondin g biochemical study showed that several axoplasmic proteins including kinesin were specifically phosphorylated by the activation of the PKA pathway, These findings suggest the possible roles of PKA in the regul ation of the direction of the axonal transport in vivo. The finding th at only vesicle transport but not mitochondria transport was inhibited also suggests that the transport of vesicles and that of mitochondria are differently regulated and might be supported by different motors.