Heterogenous expression of N- and R-type Ca²⁺ channels among large mossy fiber terminals in mouse hippocampus - 1. Physiological evidences

Abstract

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)]