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1 Department of Neurophysiology, University of Tokyo Graduate School of Medicine, Tokyo 113-0033, Japan
2 National CRI Center for Calcium and Learning, Korea Institute of Science and Technology, Seongbuk-ku, Seoul 136-791, Korea
At the nerve terminal, both N- and P/Q-type Ca2+ channels mediate synaptic transmission, with their relative contribution varying between synapses and with postnatal age. To clarify functional significance of different presynaptic Ca2+ channel subtypes, we recorded N-type and P/Q-type Ca2+ currents directly from calyces of Held nerve terminals in 
1A-subunit-deficient mice and wild-type (WT) mice, respectively. The most prominent feature of P/Q-type Ca2+ currents was activity-dependent facilitation, which was absent for N-type Ca2+ currents. EPSCs mediated by P/Q-type Ca2+ currents showed less depression during high-frequency stimulation compared with those mediated by N-type Ca2+ currents. In addition, the maximal inhibition by the GABAB receptor agonist baclofen was greater for EPSCs mediated by N-type channels than for those mediated by P/Q-type channels. These results suggest that the developmental switch of presynaptic Ca2+ channels from N- to P/Q-type may serve to increase synaptic efficacy at high frequencies of activity, securing high-fidelity synaptic transmission.
(Received 6 May 2005;
accepted after revision 20 July 2005;
first published online 21 July 2005)
Corresponding author T. Takahashi: Department of Neurophysiology, University of Tokyo Graduate School of Medicine, Tokyo 113-0033, Japan. Email: ttakahas-tky{at}umin.ac.jp
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