The mechanism of the neurotransmitter release in growth cones.
The growth cone is considered the precursor of the presynaptic terminal. To elucidate the minimal molecular machinery required for exocytosis, we examined the characteristics of alpha-latrotoxin-induced exocytosis in growth cones. In isolated growth cones (IGC), neurotransmitters were released in a SNARE-dependent manner, but rab3A cycling was blocked. By supplying rabphilin, a rab3A acceptor found in low levels in IGC, the IGC obtained as high an exocytotic efficiency as adult synaptosomes, and the complete GDP-GTP conversion of rab3A occurred on growth cone vesicles (GCV). GCVs bound SNAREs but not NSF or alpha-SNAP; whereas in the rabphilin-supplied IGC, GCVs recruited both NSF and alpha-SNAP, to form the SNARE-NSF-SNAP complex. These results suggest that rab3A cycling is dependent upon the accumulation of rabphilin and is completed later than the SNARE mechanism, and that rabphilin is involved in determining the efficiency of exocytosis by modifying the SNARE mechanism.
Igarashi
M
M
Department Molecular and Cellular Neurobiology, Gunma University School of Medicine, Maebashi, Gunma, Japan. bunshiby@news.sb.gunma-u.ac.jp
Ohyama
A
A
Ohbayashi
K
K
Kozaki
S
S
Komiya
Y
Y
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D004622:Embryo, Mammalian / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D020439:Growth Cones / Q000187:drug effects / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology; D052066:N-Ethylmaleimide-Sensitive Proteins; D009419:Nerve Tissue Proteins / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D050600:SNARE Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013111:Spider Venoms / Q000494:pharmacology; D013572:Synaptic Vesicles / Q000502:physiology; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000494:pharmacology; D020826:rab3A GTP-Binding Protein / Q000378:metabolism; D000097624:Rabphilin-3A
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D008565:Membrane Proteins; D052066:N-Ethylmaleimide-Sensitive Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D011994:Recombinant Proteins; D050600:SNARE Proteins; D052067:Soluble N-Ethylmaleimide-Sensitive Factor Attachment Proteins; D013111:Spider Venoms; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein; D000097624:Rabphilin-3A; C020763:alpha-latrotoxin; C498737:Nsf protein, rat