抄録
We have previously shown that at least four voltage-dependent Ca2+ channel (VDCC) subtypes, N, P/Q, R and L have been identified in the large mossy fiber (MF) terminals in mouse hippocampus (Tokunaga et al., 2004). The possibility was investigated that the expression of VDCC subtypes were not homogeneous among MF boutons. The dextran-conjugates of Ca2+-sensitive indicators was injected at the dentate granule cell layer of mouse hippocampal slice and allowed to be accumulated in the MF terminals. The extracellular Ca2+ was replaced with Sr2+ and the nerve stimulus-dependent Sr2+ increments were optically measured under confocal microscopy. The expression of VDCC subtypes were estimated by a specific suppression of the subtype-dependent component of Sr2+ increment by ω-conotoxin GVIA (N-type), ω-agatoxin IVA (P/Q-type) and SNX-482 (R-type), respectively. We found that conotoxin and SNX-482 sensitivities were variable among MF terminals whereas agatoxin sensitivity was not. Even two adjacent boutons in the same axon were different in the toxin sensitivities. The MF synaptic transmission was also variable in the sensitivities to conotoxin and SNX-482 but not to agatoxin. Therefore, MF terminals are suggested to be heterogenous in the expression of N- and R-type VDCCs although not in that of P/Q-type. [Jpn J Physiol 54 Suppl:S159 (2004)]
