| Project/Area Number |
02404022
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Neurophysiology and muscle physiology
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| Research Institution | Tohoku University |
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Principal Investigator |
AKAIKE Norio Tohoku Univ. Sch. Med. Professor, 医学部, 教授 (30040182)
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| Co-Investigator(Kenkyū-buntansha) |
TOKUTOMI Naofumi Tohoku Univ. Sch. Med. Assistant Professor, 医学部, 助手 (30227582)
NAKAYE Toshio Tohoku Univ. Sch. Med. Assistant Professor, 医学部, 助手 (20155659)
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| Project Period (FY) |
1990 – 1991
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥6,300,000 (Direct Cost: ¥6,300,000)
Fiscal Year 1991: ¥6,300,000 (Direct Cost: ¥6,300,000)
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| Keywords | rat hippocampal CA1 region / isolated pyramidal neuron / tetrodotoxin-sensitive Ca current / divalent cation permeability / scorpion toxin / heterogeneous distribution / kinetics / lidocaine / ラット / 海馬CA1領域 / TTX感受性Ca電流 / 単離錐体細胞 / 電気生理学 |
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| Research Abstract |
1. Voltage-dependent Ca^<2+> currents (I_<Ca>s) in neurons can be classified into T-, N-and L-types. In the CA1 pyramidal neurons freshly dissociated from rat hippocampus we found an additional tetrodotoxin (TTX) -sensitive Ca^<2+> current (termed 'TTX-I_<Ca>'). The TTX-I_<Ca> showed a heterogeneous distribution, preferentially in the dorsal site of CA1 region.
2. Activation and inactivation processes of the TTX-I_<Ca> were highly potential-dependent, and the latter was fitted by a double exponential function. The TTX-I_<Ca> was activated at a threshold potential of about-55 mV and reached full activation at-30 mV. The steady-state inactivation of TTX-I_<Ca> could be fitted by a Boltzmann equation with slope factor of 6.0 mV and a half-inactivation voltage of-72.5 mV.
3. When the peak amplitudes of TTX-I_<Ca> were plotted as a function of extracellular Ca^<2+> concentration ([Ca^<2+>]_o), the current amplitude increased linearly without showing any saturation.
4. The ratio of peak amplitude in the individual I-V relationships of Ca^<2+>, Si^<2+> and Ba^<2+> currents passing through the TTX-sensitive Ca^<2+>-conducting channel was 1 : 0.33 : 0.05, although the current kinetics were much the same.
5. TTX inhibited the TTX-I_<Ca> in time and concentration-dependent manner without affecting the current kietics. Lignocaine inhibited the TTX-I_<Ca> in a second in a concentration-dependent manner, with accelerating the inactivation process. The concentrations of half-inhibition (IC_<50>) were 3.5x10^<-9>M for TTX and 3.6x10^<-4>M for lignocaine.
6. Scorpion toxin prolonged the inactivation phase of TTX-I_<Ca> in a time-and concentration-dependent manner. In the toxin-treated neurons, both the slow time constant of inactivation (tau_<is>) and its functional contribution to the total current increased with increasing the toxin concentration.
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