2003 Fiscal Year Final Research Report Summary
Investigation on the mechanisms of transmitter release and its regulation : Imaging of ion dynamics and release process in the presynaptic nerve terminal
| Project/Area Number |
14580671
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Biophysics
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| Research Institution | Nagoya University |
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Principal Investigator |
SUZUKI Naoya Nagoya University, School of Science, Research Associate, 大学院・理学研究科, 助手 (50222063)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Presynaptic terminal / Neuro-muscular junction / Magnesium sensitive dye / Calcium ion / Magnesium ion / spontaneous release / Short-term plasticity / Casein kinase |
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| Research Abstract |
1.Tetanus-induced Mg^<2+> accumulation enhances MEPP frequency under Ca^<2+>-free conditions
Effects of Ca^<2+> on tetanic and post-tetanic enhancement of miniature end-plate potential (MEPP) frequency were examined at the frog neuromuscular junction. About thirty times enhancement of MEPP frequency was induced by 100 Hz tetanus for 50 sec in an EGTA-chelated Ca^<2+>-free Mg^<2+> containing external solution. Ca^<2+>-imaging indicated that there was no increase in [Ca^<2+>]_i at the presynaptic terminals during tetanus. Decreasing external concentration of Mg^<2+> from 5 mM to 2 mM reduced peak value of teh tetanus-induced enhancement of MEPP frequency to about a half. Blocking of N-type Ca^<2+> channels with ω-conotoxin GVIA reduced the peak value of the enhancement to about 25%. Mg^<2+>-imaging indicated that [Mg^<2+>]_i in the terminals increased to about 1.5 times during tetanus and it returned to the resting level with a time constant of about 1 min. This tetanus-induced increase i
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n [Mg^<2+>]_i was reduced to about one-third after treated with ω-conotoxin GVIA. These results suggest that Mg^<2+> accumulation in the presynaptic terminals through N-type Ca^<2+> channels is the main cause of the tetanus-induced enhancement of MEPP frequently.
2.A new type enhancement of transmitter release not depended on Ca^<2+> and Mg^<2+>
We examined whether above presynaptic activation also affected endplate potentials (EPPs). The nerve-muscle preparation was circulated with Ca^<2+>-free Ringer's solution. EPPs were evoked by 0.25Hz stimulation, simultaneously 0.9mM Ca^<2+> Ringer's solution was puffed locally to the observed synapse. Puff was stopped 3 minutes before tetanus, therefore the extracellular condition was Ca^<2+>-free during tetanus. After tetanus, EPP amplitude increased to 5 times and this enhancement decayed exponentially with a time constant of about 130s. Imaging techniques indicated that [Ca^<2+>]_i did not increased but [Mg^<2+>]_i increased in presynaptic terminals during tetanus. Under various extracellular concentrations of Mf^<2+> (2,5 and 10 mM), [Mg^<2+>]_i peak increased, but this plasticity did not change. Therefore, we concluded that this plasticity depended on neither [Ca^<2+>]_i nor [Mg^<2+>]_i. Casein kinase 2 (CK2) inhibitor, DRB, reduced this plasticity to 60%. CK2 must be partially responsible for this plasticity. Less
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Research Products
(2 results)
