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Pharmacological dissection of calcium channel subtype‐related components of strontium inflow in large mossy fiber boutons of mouse hippocampus
Author(s) -
Tokunaga Takashi,
Miyazaki Kenichi,
Koseki Makoto,
Mobarakeh Jalal Izadi,
Ishizuka Toru,
Yawo Hiromu
Publication year - 2004
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/hipo.10202
Subject(s) - chemistry , voltage dependent calcium channel , calcium channel , agonist , calcium , pharmacology , biophysics , biochemistry , receptor , biology , organic chemistry
Several subtypes of voltage‐dependent calcium channels (VDCCs) are present in the presynaptic terminals. In the mammalian hippocampus, P/Q‐, N‐, and R‐ but not L‐type VDCCs are involved in the fast transmitter release from large mossy fiber (MF) boutons, which are associated with CA3 pyramidal cell dendrites. We investigated whether L‐type VDCCs are indeed absent in these large MF boutons. With the use of Sr 2+ as the Ca 2+ substitute, the stimulus‐evoked Sr 2+ increment (Δ[Sr 2+ ] pre ) was evaluated fluorometrically. Δ[Sr 2+ ] pre appeared to be proportional to Sr 2+ inflow through VDCCs and was specifically attenuated by conventional VDCC subtype‐selective antagonists. The P/Q‐type selective ω‐agatoxin IVA (AgTx IVA ) blocked Δ[Sr 2+ ] pre with an IC 50 of 28 nM and by 30–35% at its maximum effective concentration of 0.5 μM. The N‐type selective ω‐conotoxin GVIA (CgTx GVIA ) blocked Δ[Sr 2+ ] pre with an IC 50 of 15 nM and by 20–25% at its maximum effective concentration of 1 μM. The R‐type selective SNX‐482 blocked Δ[Sr 2+ ] pre with an IC 50 of 79 nM and by 20–25% at its maximum effective concentration of 1 μM. The effects of these toxins did not overlap at their maximum effective concentrations and about 70–80% of Δ[Sr 2+ ] pre was blocked by the simultaneous exposure to these toxins. Δ[Sr 2+ ] pre component that is resistant to AgTx IVA , CgTx GVIA , and SNX‐482 was significantly potentiated by an L‐type agonist, (S)‐(−)‐Bay K8644, and attenuated by an L‐type antagonist, nimodipine, suggesting that L‐type VDCCs are present in large MF terminals. The L‐type agonist, (±)‐Bay K8644, also potentiated Sr 2+ inflow into individual boutons identified as large MF boutons under confocal microscopy. Almost similar results were observed for Ca 2+ inflow‐dependent fluorescence increments. L‐type VDCCs appear to be present in large MF boutons and mediate a substantial Ca 2+ inflow into presynaptic terminals during action potentials. © 2004 Wiley‐Liss, Inc.